0001517022-26-000020 | 10-K | XBRL Viewer

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PRODUCT REVENUE AND PROVISIONS FOR VARIABLE CONSIDERATION - Schedule of Product Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Total revenues	$ 236,196	$ 160,180	$ 194,623
Product revenue, net
Disaggregation of Revenue [Line Items]
Total revenues	227,332	152,180	170,301
Vafseo
Disaggregation of Revenue [Line Items]
Total revenues	45,790	0	0
Auryxia
Disaggregation of Revenue [Line Items]
Total revenues	$ 181,542	$ 152,180	$ 170,301

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details

Cybersecurity Risk Management and Strategy Disclosure	12 Months Ended
Cybersecurity Risk Management and Strategy Disclosure	Dec. 31, 2025
Cybersecurity Risk Management, Strategy, and Governance [Line Items]
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]	We have certain processes for assessing, identifying, and managing material risks from cybersecurity threats, which are integrated into our enterprise risk management processes. Specifically, we have processes for: •Identifying and Managing Cybersecurity Risks — We have implemented a cross-functional approach to assessing, identifying and managing material cybersecurity threats and incidents. We periodically review, assess, update and test our policies, standards, processes and practices in a manner intended to address cybersecurity threats and events. The results of such reviews, assessments and tests are evaluated by management and reported to our Audit Committee of the Board of Directors, or the Audit Committee, and our Board of Directors. •Technical Safeguards — We have integrated cybersecurity into our overall information technology operations and designed our processes and systems to help protect our information assets and operations from internal and external cyber threats, protect employee and patient information from unauthorized access or attack as well as secure our networks and systems. •Incident Response and Recovery Planning — To better facilitate our cybersecurity program, our cybersecurity team works collaboratively across our Company to implement programs designed to protect our information systems from cybersecurity threats and to promptly respond to any material cybersecurity incidents. We conduct periodic tabletop exercises, including incident simulations to test these plans and ensure personnel are familiar with their roles and responsibilities in a response scenario. •Third-Party Risk Management — We maintain a risk-based approach to identifying and overseeing material cybersecurity threats presented by third parties and the systems of third parties that could adversely impact our business in the event of a material cybersecurity incident affecting those third-party systems. Also, we engage certain external cybersecurity firms to enhance our cybersecurity oversight and cybersecurity breach detection over third party service providers. •Education and Awareness — We provide training regarding cybersecurity threats as a means to equip our employees and consultants with tools to make employees and consultants aware of and to address cybersecurity threats, and to communicate our evolving information security policies, standards, processes and practices. We also use technology-based tools to mitigate cybersecurity risks and to bolster our employee-based cybersecurity programs. We adjust our cybersecurity policies, standards, processes, and practices as necessary based on the information provided by our assessments, audits and reviews. Such processes include (i) procedural and technical safeguards, (ii) response plans, (iii) periodic tests on our systems, (iv) incident simulations and (v) routine review of our cybersecurity policies and procedures to identify risks and improve our practices. We engage certain external cybersecurity firms to enhance our cybersecurity oversight. We include confidentiality provisions in all contracts with third-party service providers, and data protection provisions in certain contracts with third-party service providers where applicable, to help protect us and our employees and patients from any related vulnerabilities.
Cybersecurity Risk Management Processes Integrated [Flag]	true
Cybersecurity Risk Management Processes Integrated [Text Block]	We have certain processes for assessing, identifying, and managing material risks from cybersecurity threats, which are integrated into our enterprise risk management processes.
Cybersecurity Risk Management Third Party Engaged [Flag]	true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag]	true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]	false
Cybersecurity Risk Board of Directors Oversight [Text Block]	Our Board of Directors is responsible for exercising oversight of management’s identification and management of, and planning for, risks from cybersecurity threats. While the full Board of Directors has overall responsibility for risk oversight, the Board of Directors has delegated oversight responsibility related to risks from cybersecurity threats to the Audit Committee of our Board of Directors.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]	While the full Board of Directors has overall responsibility for risk oversight, the Board of Directors has delegated oversight responsibility related to risks from cybersecurity threats to the Audit Committee of our Board of Directors.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Audit Committee reports to the Board of Directors at least annually, and notifies the Board of Directors as necessary regarding significant new cybersecurity threats or incidents. The Audit Committee meets annually to discuss our approach to overseeing cybersecurity threats with management, including with members of our internal cybersecurity team.
Cybersecurity Risk Role of Management [Text Block]	While the full Board of Directors has overall responsibility for risk oversight, the Board of Directors has delegated oversight responsibility related to risks from cybersecurity threats to the Audit Committee of our Board of Directors. The Audit Committee reports to the Board of Directors at least annually, and notifies the Board of Directors as necessary regarding significant new cybersecurity threats or incidents. The Audit Committee meets annually to discuss our approach to overseeing cybersecurity threats with management, including with members of our internal cybersecurity team. We use an internal management team to run our information technology and cybersecurity functions, which includes our vice president of information technology and information security leads, who have collectively served in various roles in information technology and information security for over 25 years, including at other public companies. Through ongoing communications with this management committee, senior management is informed about and monitors the prevention, detection, mitigation and remediation of cybersecurity threats and incidents in real-time and reports such threats and incidents to the Audit Committee, when appropriate. Management updates the Audit Committee quarterly regarding our cybersecurity threat risk management and strategy programs. Members of the Audit Committee are also encouraged to regularly engage in ad hoc conversations with management on cybersecurity-related topics and discuss any updates to our cybersecurity risk management and strategy programs. The Audit Committee is notified between such updates regarding significant new cybersecurity threats or incidents that meet pre-established reporting thresholds and any ongoing updates regarding any risk, as needed.
Cybersecurity Risk Management Positions or Committees Responsible [Flag]	true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block]	We use an internal management team to run our information technology and cybersecurity functions, which includes our vice president of information technology and information security leads, who have collectively served in various roles in information technology and information security for over 25 years, including at other public companies.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block]	We use an internal management team to run our information technology and cybersecurity functions, which includes our vice president of information technology and information security leads, who have collectively served in various roles in information technology and information security for over 25 years, including at other public companies.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]	We use an internal management team to run our information technology and cybersecurity functions, which includes our vice president of information technology and information security leads, who have collectively served in various roles in information technology and information security for over 25 years, including at other public companies. Through ongoing communications with this management committee, senior management is informed about and monitors the prevention, detection, mitigation and remediation of cybersecurity threats and incidents in real-time and reports such threats and incidents to the Audit Committee, when appropriate. Management updates the Audit Committee quarterly regarding our cybersecurity threat risk management and strategy programs. Members of the Audit Committee are also encouraged to regularly engage in ad hoc conversations with management on cybersecurity-related topics and discuss any updates to our cybersecurity risk management and strategy programs. The Audit Committee is notified between such updates regarding significant new cybersecurity threats or incidents that meet pre-established reporting thresholds and any ongoing updates regarding any risk, as needed.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag]	true

INVENTORIES

12 Months Ended

Dec. 31, 2025

Inventory Disclosure [Abstract]

INVENTORIES

Inventories consists of the following (in thousands):


	December 31,
Inventories, current:	2025		2024
Work-in-process	$	12,651	$	12,031
Finished goods	2,959		4,212
Inventories, current	$	15,610	$	16,243
Long-term inventories included in other long-term assets:
Raw materials	50		381
Work-in-process	57,290		34,572
Finished goods	1,789		—
Inventories, long-term	59,129		34,953
Total inventories	$	74,739	$	51,196

Inventory written down as a result of excess, obsolescence, scrap or other reasons charged to cost of product and other revenue in the consolidated statements of operations and comprehensive loss was $2.5 million, $4.2 million and $1.6 million during the years ended December 31, 2025, 2024 and 2023, respectively. For the years ended December 31, 2024 and 2023, the Company realized $12.3 million and $4.3 million, respectively, of lower cost of product and other revenue due to the Company's ability to sell inventory previously written down to zero, its then net realizable value.

LIABILITY RELATED TO SETTLEMENT ROYALTIES, WORKING CAPITAL FUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES - Schedule of Liability Related to Working Capital Funds (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Other Liabilities Disclosure [Abstract]
Current portion	$ 17,356	$ 2,274
Long-term portion	22,606	38,013
Total Working Capital Fund liability	$ 39,962	$ 40,287

Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2025	Feb. 23, 2026	Jun. 30, 2025
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2025
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-36352
Entity Registrant Name	AKEBIA THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-8756903
Entity Address, Address Line One	245 First Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	871-2098
Title of 12(b) Security	Common Stock, $0.00001 par value per share
Trading Symbol	AKBA
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 946,381,036
Entity Common Stock, Shares Outstanding		267,879,239
Documents Incorporated by Reference	The registrant intends to file a definitive proxy statement pursuant to Regulation 14A in connection with its 2026 Annual Meeting of Stockholders within 120 days after the end of the registrant’s fiscal year ended December 31, 2025. Portions of the proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.
Amendment Flag	false
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Entity Central Index Key	0001517022

INCOME TAXES - Schedule of Unrecognized Tax Benefits Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits, beginning balance	$ 0	$ 0	$ 2,697
Reductions based on tax positions of current years	0	0	(2,697)
Unrecognized tax benefits, ending balance	$ 0	$ 0	$ 0

SEGMENT INFORMATION (Tables)

12 Months Ended

Dec. 31, 2025

Segment Reporting [Abstract]

Schedule of Segment Financial Information

The following table presents information about reported segment revenues, segment profit and significant segment expenses for the years ended December 31, 2025, 2024 and 2023:


	Years Ended December 31,
	2025		2024		2023
Revenues	$	236,196	$	160,180	$	194,623
Less:
Direct cost of product and other revenue	28,136		15,970		26,525
Panion royalty	11,326		9,097		10,048
Excess firm purchase commitment charge	—		2,068		1,533
Amortization of intangible asset	—		36,042		36,042
Research and development	62,359		37,652		63,079
Selling, general and administrative	107,480		106,545		100,233
License	3,396		3,220		3,237
Restructuring	—		58		181
Income (loss) from operations	23,499		(50,472)		(46,256)

Other income (expense)
Interest expense	(24,179)		(18,185)		(6,032)
Other income	58		94		887
Change in fair value of warrant liability	(3,099)		(330)		—
Loss on extinguishment of debt	—		(517)		—
Loss on termination of lease	—		—		(524)
Net loss before income taxes	(3,721)		(69,410)		(51,925)
Income tax expense	(1,624)		—		—
Net loss	$	(5,345)	$	(69,410)	$	(51,925)

LIABILITY RELATED TO SETTLEMENT ROYALTIES, WORKING CAPITAL FUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES - Schedule of Liability Related to Settlement Royalties (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Other Liabilities Disclosure [Abstract]
Current portion (included in accrued expenses and other current liabilities)	$ 12,516	$ 5,924
Long-term portion	54,750	46,697
Total settlement royalties liability	$ 67,266	$ 52,621

INCOME TAXES - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Current:
Federal	$ 0	$ 0	$ 0
State	1,624	0	0
Foreign	0	0	0
Total current	1,624	0	0
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	0	0	0
Total deferred	0	0	0
Total income taxes	$ 1,624	$ 0	$ 0

PRODUCT REVENUE AND PROVISIONS FOR VARIABLE CONSIDERATION - Schedule of Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Accounts receivable
Contract assets:
Additions	$ 8,894	$ 8,562
Deductions	(8,513)	(9,885)
Deferred revenue
Contract liability:
Additions	0	0
Deductions	0	(43,296)
Accounts receivable
Contract assets:
Balance at Beginning of Period	2,010	3,333
Balance at End of Period	2,391	2,010
Deferred revenue
Contract liability:
Balance at Beginning of Period	0	43,296
Balance at End of Period	0	0
Sales to AG Partner \| Accounts receivable
Contract assets:
Additions	12,006
Deductions	(11,812)
Sales to AG Partner \| Deferred revenue
Contract liability:
Additions	10,675
Deductions	(7,994)
Sales to AG Partner \| Accounts receivable
Contract assets:
Balance at Beginning of Period	0
Balance at End of Period	194	0
Sales to AG Partner \| Deferred revenue
Contract liability:
Balance at Beginning of Period	0
Balance at End of Period	$ 2,681	$ 0

NET LOSS PER SHARE (Tables)

12 Months Ended

Dec. 31, 2025

Earnings Per Share [Abstract]

Schedule of Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share

The shares in the table below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, due to their anti-dilutive effect:


	Years Ended December 31,
	2025	2024	2023
Warrants	2,115,385	3,076,923	—
Outstanding common stock options	17,516,945	16,049,012	12,690,624
Unvested restricted stock units	6,323,229	5,429,790	3,930,167
Stock appreciation rights	635,313	635,313	635,313
Total	26,590,872	25,191,038	17,256,104

PRODUCT REVENUE AND PROVISIONS FOR VARIABLE CONSIDERATION - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Product revenue, net
Disaggregation of Revenue [Line Items]
Accounts receivable, net	$ 44.4	$ 32.4

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

ADDITIONAL BALANCE SHEET DETAIL

12 Months Ended

Dec. 31, 2025

Payables and Accruals [Abstract]

ADDITIONAL BALANCE SHEET DETAIL

Prepaid expenses and other current assets are as follows (in thousands):


	December 31,
Description	2025	2024
Prepaid manufacturing	—	4,029
Restricted cash	1,699	—
Other	3,771	7,321
Total prepaid expenses and other current assets	5,470	11,350

Prepaid manufacturing expenses include advance payments to contract manufacturing organizations, or CMOs, for APIs or drug substance. Such amounts are reclassified to work-in-process inventory upon the quality release of the batches and transfer of title to the Company from the CMO.

Other prepaid expenses and other current assets, among other things, include capitalized implementation costs, prepaid insurance and prepaid information technology costs.

Other long-term assets are as follows (in thousands):


	December 31,
Description	2025		2024
Long-term inventories	$	59,129	$	34,953
Restricted cash	—		1,680
Other	552		744
Total other long-term assets	$	59,681	$	37,377

See Note 4, Inventories, for further information on long-term inventories.

Accrued expenses and other current liabilities are as follows (in thousands):


	December 31,
Description	2025		2024
Product revenue allowances	$	7,916	$	9,657
Product rebates	64,674		6,070
Product return provisions, current portion	2,375		5,295
Compensation and related benefits	11,018		9,194
Operating lease liabilities, current portion	3,548		5,400
Royalties due to Panion & BF Biotech, Inc.	3,924		3,543
Liability related to sale of future royalties, current portion	1,664		2,039
Professional fees	1,597		1,452
Accrued manufacturing costs	1,808		1,468
BioVectra, Inc. termination fees, current portion	—		7,204
Settlement royalties liability, current portion	12,516		5,924
Clinical trial costs	1,188		1,885
Restructuring costs, current portion	—		489
Payments due to Q32	5,000		—
Other	4,488		3,840
Total accrued expenses and other current liabilities	$	121,716	$	63,460

LICENSE, COLLABORATION AND OTHER REVENUE - JT and Torii Sublicense Agreement - Narrative (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2013 USD ($) performance_obligation	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue		$ 236,196	$ 160,180	$ 194,623
Accounts receivable, net		47,031	34,368
JT and Torii \| Sublicense Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential payment for achievement of annual net sales milestones	$ 55,000
License agreement, notice period for termination	6 months
Prior written notice for termination on the breach of agreement period	60 days
Number of performance obligations \| performance_obligation	2
Recognized revenue		5,700	$ 5,400	$ 5,400
Accounts receivable, net		$ 1,500

- Definition

+ References

+ Details

LEASES

12 Months Ended

Dec. 31, 2025

Leases [Abstract]

LEASES

Cambridge Lease

Under the Cambridge Lease, the Company leases approximately 65,167 square feet of office, storage and laboratory space in Cambridge, Massachusetts. The term of the Cambridge Lease with respect to the 59,216 square feet of office and storage space expires on September 11, 2026, with one five-year extension option available. The term of the Cambridge Lease with respect to the 5,951 square feet of the laboratory space expires on September 11, 2026, with one two-year extension option available. In addition to rent, the Company is required to pay additional amounts for taxes, insurance, maintenance, and other operating expenses.

The Cambridge Lease is non-cancelable and is classified as an operating lease. The renewal options with respect to the office, storage and the lab space of the Cambridge Lease were not included in the calculation of the right-of-use asset and operating lease liability as the renewals were not reasonably certain. The Cambridge Lease does not contain residual value guarantees. The components of lease right-of-use assets and lease liabilities are included in the consolidated balance sheets. Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, the Company used its incremental borrowing rate when measuring operating lease liabilities. In arriving at the operating lease liabilities, the Company applied incremental borrowing rates ranging from 6.65% to 6.94%, which were based on the remaining lease term at either the date of adoption of ASC 842, Leases, or the effective date of any subsequent lease term extensions. As of December 31, 2025, the remaining lease term for the Cambridge Lease was 0.70 years.

Operating lease costs were $5.0 million for each of the years ended December 31, 2025 and 2024 and $5.7 million for the year ended December 31, 2023. Cash paid for amounts included in the measurement of operating lease liabilities were $5.8 million, $5.7 million and $5.9 million for the years ended December 31, 2025, 2024 and 2023, respectively. The security deposit in connection with the Cambridge Lease is $1.7 million in the form of a letter of credit, which is included as restricted cash in prepaid expenses and other current assets in the Company's consolidated balance sheet as of December 31, 2025 and in other long-term assets in the Company's consolidated balance sheet as of December 31, 2024.

Sublease and Former Boston Lease

Previously, the Company leased 27,924 square feet of office space in Boston, Massachusetts, or the Boston Lease, under a non-cancelable operating lease that was set to expire in July 2031. The Company subleased the entire Boston Lease, effective October 2019 through February 2023. The Company recorded no rental income for each of the years ended December 31, 2025 and 2024 and $0.3 million in rental income as other income in the consolidated statements of operations and comprehensive loss during the year ended December 31, 2023.

In May 2023, pursuant to a Lease Assignment Agreement, or the Lease Assignment Agreement, the Company assigned all of its rights, title, and interest in, to, and under the Boston Lease to LG Chem Life Sciences Innovation Center, Inc., or LG Chem, and made a payment to LG Chem of $1.3 million. As of May 2023, LG Chem assumed all of the rights and obligations of the Company under the Boston Lease and the Company has no further obligations for rent or other payments under the Boston Lease. In accordance with ASC 842, Leases, the Company wrote off the right-of-use asset and lease liability associated with the Boston Lease, and recognized the difference between the right-of-use asset and the lease liability offset by the $1.3 million payment as a loss on lease termination in the consolidated statements of operations and comprehensive loss of $0.5 million during the year ended December 31, 2023.

Future Lease Commitments

Future commitments under the non-cancelable Cambridge Lease are as follows (in thousands):


	Operating Lease
2026	$	3,613


Less: present value adjustment	(65)
Current operating lease liabilities	$	3,548

See Note 18, Subsequent Events, for information regarding the Waltham Lease (as defined below).

FAIR VALUE MEASUREMENTS

12 Months Ended

Dec. 31, 2025

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

The tables below present certain assets and liabilities measured at fair value categorized by the level of input used in the valuation of each asset and liability (in thousands):


	December 31, 2025
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	172,689	$	—	$	—	$	172,689
Long-term liability:
Warrant liability	$	—	$	2,980	—		$	2,980


	December 31, 2024
	Level 1		Level 2		Level 3	Total
Long-term liability:
Warrant liability	$	—	$	5,176	—	$	5,176

Cash and cash equivalents —Money market funds included within cash and cash equivalents are classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices in active markets. As of December 31, 2024, the Company did not have any money market funds included in cash equivalents.

Warrant liability – The warrant liability is classified within Level 2 of the fair value hierarchy because it is valued using inputs which are observable either directly or indirectly. The fair value was calculated using the Black-Scholes option pricing model using the following key inputs: volatility, risk-free rate, dividend yield and expected term.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
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-Name Accounting Standards Codification
-Section 55
-Paragraph 107
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-107

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
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-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (h)
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-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 940
-SubTopic 820
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478119/940-820-50-1

+ Details

NET LOSS PER SHARE

12 Months Ended

Dec. 31, 2025

Earnings Per Share [Abstract]

NET LOSS PER SHARE

Potentially dilutive securities including common stock options, RSUs, SARs and warrants have been excluded from the calculation of diluted net loss per share as their effects would be anti-dilutive. For periods in which the Company reports a net loss, the weighted average number of shares outstanding used to calculate both basic and diluted net loss per share were the same. The shares in the table below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, due to their anti-dilutive effect:


	Years Ended December 31,
	2025	2024	2023
Warrants	2,115,385	3,076,923	—
Outstanding common stock options	17,516,945	16,049,012	12,690,624
Unvested restricted stock units	6,323,229	5,429,790	3,930,167
Stock appreciation rights	635,313	635,313	635,313
Total	26,590,872	25,191,038	17,256,104

INCOME TAXES - Schedule of Effective Income Tax Rate Differs From Statutory Federal Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
U.S. federal tax at statutory rate	21.00%	21.00%	21.00%
State and local tax at statutory rate	(34.50%)	0.60%	2.70%
Research and development tax credits		1.90%	0.30%
Change in valuation allowance	14.30%	(32.50%)	(9.10%)
Other permanent differences		(1.70%)	(2.00%)
Stock option cancellations		(1.80%)	(3.70%)
Stock option shortfalls		0.00%	(1.70%)
Effect of rate changes		13.50%	(7.70%)
Provision to return adjustment		(1.00%)	(0.30%)
Other	(0.60%)	0.00%	0.50%
Effective tax rate	(43.70%)	0.00%	0.00%

ADDITIONAL BALANCE SHEET DETAIL - Schedule of Accrued Expenses and other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Payables and Accruals [Abstract]
Product revenue allowances	$ 7,916	$ 9,657
Product rebates	64,674	6,070
Product return provisions, current portion	2,375	5,295
Compensation and related benefits	11,018	9,194
Operating lease liabilities, current portion	3,548	5,400
Royalties due to Panion & BF Biotech, Inc.	3,924	3,543
Liability related to sale of future royalties, current portion	1,664	2,039
Professional fees	1,597	1,452
Accrued manufacturing costs	1,808	1,468
BioVectra, Inc. termination fees, current portion	0	7,204
Settlement royalties liability, current portion	12,516	5,924
Clinical trial costs	1,188	1,885
Restructuring costs, current portion	0	489
Payments due to Q32	5,000	0
Other	4,488	3,840
Total accrued expenses and other current liabilities	$ 121,716	$ 63,460
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Total accrued expenses and other current liabilities	Total accrued expenses and other current liabilities

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS (Tables)

12 Months Ended

Dec. 31, 2025

Equity [Abstract]

Schedule of Equity Plans

The following table contains information about the Company's equity incentive plans:


			December 31, 2025		December 31, 2024
Title of Plan	Group Eligible	Type of Award Granted (or to be Granted)	Awards Outstanding	Additional Awards Available for Grant	Awards Outstanding	Additional Awards Available for Grant
Keryx Equity Plans(1)(2)	Employees, directors and consultants	Common stock options and RSUs	148,860	—	163,765	—

Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (2) (3) (the 2014 Plan) (replaces 2008 Plan)	Employees, directors, consultants and advisors	Common stock options, RSUs, SARs and performance awards	8,412,898	—	11,559,708	—
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan, as amended(3) (the 2023 Plan) (replaces 2014 Plan)	Employees, officers, directors, consultants and advisors	Common stock options, SARs, restricted stock, unrestricted stock, RSUs, performance awards, other share-based awards and dividend equivalents	15,913,729	24,723,655	10,390,642	11,340,648

(1) The Keryx Equity Plans consist of the Keryx Biopharmaceuticals, Inc. 1999 Share Option Plan, Keryx Biopharmaceuticals, Inc., as amended, the 2004 Long-Term Incentive Plan, as amended, the Keryx Biopharmaceuticals, Inc. 2007 Incentive Plan, the Keryx Biopharmaceuticals Inc. Amended and Restated 2013 Incentive Plan and the Keryx Biopharmaceuticals, Inc. 2018 Equity Incentive Plan.

(2) New awards are no longer being granted under these plans.

(3) This table includes the following inducement awards that are subject to the terms and conditions of the applicable plan but were granted as inducement awards consistent with Nasdaq Listing Rule 5635(c)(4) and not under the applicable plan: 1,050,525 options outstanding under the 2014 Plan and 3,034,085 options outstanding under the 2023 Plan as of December 31, 2025 and 1,151,127 options outstanding under the 2014 Plan and 2,534,775 options outstanding under the 2023 Plan as of December 31, 2024.

(4) On June 10, 2025, the 2023 Plan was amended to increase the number of shares of common stock available for issuance thereunder by 18,900,000 shares.

Schedule of Stock Option Activity

The combined stock option activity for the year ended December 31, 2025, is as follows:


	Stock Options	Weighted-Average Exercise Price		Weighted-Average Contractual Life (years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2024	16,684,325	$	3.19	7.17 years	$	6,797
Granted	5,464,077	$	2.48
Exercised	(1,205,853)	$	1.40
Expired	(1,165,336)	$	8.67
Canceled and forfeited	(1,624,955)	$	1.99
Outstanding at December 31, 2025	18,152,258	$	2.85	6.97 years	$	3,690
Exercisable at December 31, 2025	9,819,097	$	3.56	5.59 years	$	2,624
Vested and expected to vest at December 31, 2025	18,152,258	$	2.85	6.97 years	$	3,690

Schedule of RSU and PSU Activity

RSU and PSU activity is as follows:


	2014 Plan		2023 Plan
	Number of Shares	Weighted Average Grant Date Fair Value	Number of Shares	Weighted Average Grant Date Fair Value
Unvested as of December 31, 2024	1,321,423	$0.95	4,108,367	$1.59
Granted	—	$0.00	4,492,000	$2.31
Vested	(849,701)	$1.06	(1,636,898)	$1.55
Forfeited and canceled	(141,100)	$0.98	(970,862)	$1.89
Unvested as of December 31, 2025	330,622	$0.63	5,992,607	$2.09

Schedule of Assumptions Used in Black-Scholes Option Pricing Model

The weighted-average assumptions used in calculating the fair values of the rights to acquire stock under the 2023 Plan, the 2014 Plan and inducement awards were as follows:


	Years ended December 31,
Common Stock Options	2025			2024			2023
Risk-free interest rate	3.67%	-	4.38%	3.60%	-	4.66%	3.54%	-	4.81%
Expected volatility	111.61%	-	123.58%	109.98%	-	119.81%	100.97%	-	111.71%
Expected term (years)	5.51	-	6.25	5.51	-	6.25	5.51	-	6.25
Expected dividend yield	—%			—%			—%
Weighted average grant date fair value	$2.14			$1.36			$0.69

Schedule of Stock-Based Compensation Expense in Consolidated Statement of Operations and Comprehensive Loss

The Company has classified stock-based compensation in its consolidated statements of operations and comprehensive loss as follows (in thousands):


	Years ended December 31,
	2025		2024		2023
Cost of goods sold	$	683	$	399	267
Research and development	2,120		1,498		1,964
Selling, general and administrative	8,480		5,840		6,456
Restructuring	—		38		630
Total	$	11,283	$	7,775	$	9,317

Schedule of Stock-Based Compensation Expense by Type of Award

Stock-based compensation by type of award was as follows (in thousands):


	Years ended December 31,
	2025		2024		2023
Stock options	$	5,356	$	4,036	$	5,310
Restricted stock units	5,214		3,655		3,637
Performance RSUs	545		—		297
Employee stock purchase plan	168		84		73
Total	$	11,283	$	7,775	$	9,317

COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands					1 Months Ended					3 Months Ended	12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands	Nov. 28, 2025 USD ($)	Dec. 22, 2022 USD ($) quarterly_payment	Feb. 10, 2021	Apr. 17, 2019	Dec. 31, 2025 USD ($)	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2020	Jun. 30, 2021 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Other Commitments [Line Items]
Change in excess firm purchase commitment liability											$ 0	$ 2,100	$ 1,500
Research and development											62,359	37,652	63,079
Contract cost incurred in research and development activities											82,600
Charge for purchase of IPR&D asset											12,807	0	0
Siegfried Evionnaz SA
Other Commitments [Line Items]
Cost of purchased minimum quantity product					$ 800						800
Excess firm purchase commitment charge											800	3,600
Patheon \| Vafseo Drug Product
Other Commitments [Line Items]
Purchase commitment, option for non-auto renewal, prior written notice period (in months)									18 months
Minimum purchase commitment					1,100						1,100
STA Pharmaceutical Hong Kong Limited
Other Commitments [Line Items]
Excess firm purchase commitment charge											69,200
WuXi STA
Other Commitments [Line Items]
Excess firm purchase commitment charge											1,800
Purchase commitment, option to extend, prior notice period (in months)			18 months
Long-term purchase commitment, option to terminate, prior notice period (at least)			180 days
BioVectra Inc
Other Commitments [Line Items]
Long-term purchase commitment, termination amount payable		$ 32,500
Long-term purchase commitment, upfront payment termination amount		$ 17,500
Long-term purchase commitment, termination amount payable after upfront payment, number of quarterly periods \| quarterly_payment		6
Long-term purchase commitment, termination amount payable after upfront payment, per quarter		$ 2,500
Long-term purchase commitment, termination amount payable after upfront payment		$ 15,000
Long-term purchase commitment, imputed interest on termination amount payable		17.00%
Long-term purchase commitment, upfront termination amount classified as cost of goods sold		$ 11,200
Amortization discount											300	1,600	1,900
Panion & BF Biotech, Inc \| License Agreement
Other Commitments [Line Items]
License agreement, notice period for termination				90 days
Royalty payments											$ 11,300	9,100	$ 10,000
Cyclerion \| License Agreement
Other Commitments [Line Items]
Expiration period beginning with first commercial sale (in years)											10 years
Termination period, prior written notice (in days)											180 days
Cyclerion \| License Agreement \| Acquired Licenses
Other Commitments [Line Items]
Upfront payments										$ 3,000
Cyclerion \| License Agreement \| Acquired Licenses \| Research and development
Other Commitments [Line Items]
Upfront payments								$ 3,000
Cyclerion \| Cyclerion Amendment \| Acquired Licenses
Other Commitments [Line Items]
Upfront payments						$ 500	$ 1,250
Specified development and regulatory milestone payments, contingent on a product-by-product basis											$ 197,500
Research and development					$ 1,000
Cyclerion \| Cyclerion Amendment \| Acquired Licenses \| Maximum
Other Commitments [Line Items]
Tiered royalties (as percent)					20.00%						20.00%
Cyclerion \| Cyclerion Amendment \| Acquired Licenses \| Research and development
Other Commitments [Line Items]
Upfront payments												1,250
Contingent consideration												$ 500
Cyclerion \| Cyclerion Amendment \| Acquired Licenses \| Accrued Liabilities
Other Commitments [Line Items]
Contingent consideration											$ 1,000
Q32 \| Q32 Asset Purchase Agreement
Other Commitments [Line Items]
Upfront payments	$ 12,800
Specified development and regulatory milestone payments, contingent on a product-by-product basis	94,500
Upfront payment	7,000
Additional upfront payment	$ 3,000										3,000
Additional payment term	6 months
Development milestone payment	$ 2,000										2,000
Commercial milestone payment	487,500
Asset acquisition, consideration transferred, transaction cost	$ 800
Charge for purchase of IPR&D asset											$ 12,800

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Revenues:
Total revenues	$ 236,196	$ 160,180	$ 194,623
Cost of goods sold:
Cost of product and other revenue	39,462	27,135	38,107
Amortization of intangible asset	0	36,042	36,042
Total cost of goods sold	39,462	63,177	74,149
Operating expenses:
Research and development	62,359	37,652	63,079
Selling, general and administrative	107,480	106,545	100,233
License	3,396	3,220	3,237
Restructuring	0	58	181
Total operating expenses	173,235	147,475	166,730
Income (loss) from operations	23,499	(50,472)	(46,256)
Other income (expense):
Interest expense	(24,179)	(18,185)	(6,032)
Other income	58	94	887
Change in fair value of warrant liability	(3,099)	(330)	0
Loss on extinguishment of debt	0	(517)	0
Loss on termination of lease	0	0	(524)
Loss before income taxes	(3,721)	(69,410)	(51,925)
Income tax expense	(1,624)	0	0
Net loss	(5,345)	(69,410)	(51,925)
Comprehensive loss	$ (5,345)	$ (69,410)	$ (51,925)
Net loss per share:
Basic (in dollars per share)	$ (0.02)	$ (0.33)	$ (0.28)
Diluted (in dollars per share)	$ (0.02)	$ (0.33)	$ (0.28)
Weighted average number of common shares outstanding:
Basic (in shares)	257,157,782	210,946,658	187,465,448
Diluted (in shares)	257,157,782	210,946,658	187,465,448
Product revenue, net
Revenues:
Total revenues	$ 227,332	$ 152,180	$ 170,301
License, collaboration and other revenue
Revenues:
Total revenues	$ 8,864	$ 8,000	$ 24,322

INVENTORIES (Tables)

12 Months Ended

Dec. 31, 2025

Inventory Disclosure [Abstract]

Schedule of Components Inventory

Inventories consists of the following (in thousands):


	December 31,
Inventories, current:	2025		2024
Work-in-process	$	12,651	$	12,031
Finished goods	2,959		4,212
Inventories, current	$	15,610	$	16,243
Long-term inventories included in other long-term assets:
Raw materials	50		381
Work-in-process	57,290		34,572
Finished goods	1,789		—
Inventories, long-term	59,129		34,953
Total inventories	$	74,739	$	51,196

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2025

Income Tax Disclosure [Abstract]

Schedule of Income Before Provision

Income before provision for income taxes was as follows (in thousands):


	Years Ended December 31,
	2025		2024		2023
United States	$	(3,721)	$	(69,410)	$	(51,925)
Foreign	—		—		—
Income (loss) before taxes	$	(3,721)	$	(69,410)	$	(51,925)

Schedule of Provision for Income Taxes

The Company’s income tax provision was computed based on the federal statutory rate and the state statutory rates, net of the related federal benefit. The components of provision for income taxes for all periods presented were as follows (in thousands):


	Years Ended December 31,
	2025		2024		2023
Current:
Federal	$	—	$	—	$	—
State	1,624		—		—
Foreign	—		—		—
Total current	1,624		—		—
Deferred:
Federal	—		—		—
State	—		—		—
Foreign	—		—		—
Total deferred	—		—		—
Total income taxes	$	1,624	$	—	$	—

Schedule of Effective Income Tax Rate Differs From Statutory Federal Income Tax Rate

A reconciliation of the provision for income taxes to the amount computed by applying the 21% statutory U.S. federal income tax rate to income before income taxes after the adoption of ASU 2023-09 is as follows:


	Year Ended December 31,
	2025
	(In thousands)		Percent
U.S. federal statutory tax rate	$	(781)	21.0	%
State and local income taxes, net of federal income tax effect(1)	1,283		(34.5)
Tax credits
Research and development tax credits	(988)		26.6
Changes in valuation allowances	(533)		14.3
Nontaxable or nondeductible items
Meals & entertainment	165		(4.4)
Lobbying contributions	294		(7.9)
Stock compensation	680		(18.3)
162(m) compensation limit	731		(19.6)
Pharma fee	105		(2.8)
Warrant liability	651		(17.5)
Other Adjustments
Other	18		(0.6)
Effective tax rate	$	1,624	(43.7)	%

(1) The states and local jurisdictions that contribute to the majority (greater than 50%) of the tax effect in this category include Tennessee.


	Years Ended December 31,
	2024		2023
U.S. federal tax at statutory rate	21.0	%	21.0	%
State and local tax at statutory rate	0.6		2.7
Research and development tax credits	1.9		0.3
Change in valuation allowance	(32.5)		(9.1)
Other permanent differences	(1.7)		(2.0)
Stock option cancellations	(1.8)		(3.7)
Stock option shortfalls	—		(1.7)
Effect of rate changes	13.5		(7.7)
Provision to return adjustment	(1.0)		(0.3)

Other	—		0.5
Effective tax rate	—	%	—	%

Schedule of Significant Components of Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities are as follows (in thousands):


	December 31,
	2025		2024
Deferred tax assets:
Accrued expenses and other current liabilities	$	9,374	$	1,757
Deferred revenue	15,765		13,222
Sale of royalty	12,251		13,595
R&D credits	7,726		6,152
Capitalized R&D costs	11,873		21,270
Net operating loss carryforward	289,712		291,723
ASC 842 lease liability	832		2,248
Working Capital Fund liability	9,366		10,123
Intangible assets	4,631		2,040
Other	22,021		29,048
Total deferred tax assets	383,551		391,178
Less valuation allowance	(382,001)		(387,803)
Total deferred tax assets, net of valuation allowance	1,550		3,375
Deferred tax liabilities:

481(a) adjustments	(670)		(1,271)
ROU asset (ASC 842)	(859)		(2,065)
Other	(21)		(39)
Total deferred tax liabilities	(1,550)		(3,375)
Net deferred tax liability	$	—	$	—

Schedule of Unrecognized Tax Benefits Roll Forward

A reconciliation of the beginning and ending amounts of unrecognized tax benefits for the years ending December 31, 2025, 2024 and 2023 are as follows (in thousands):


Balance at December 31, 2022	$	2,697
Reductions based on tax positions of current years	(2,697)
Balance at December 31, 2023	—
Reductions based on tax positions of current years	—
Balance at December 31, 2024	—
Reductions based on tax positions of current years	—
Balance at December 31, 2025	$	—

SEGMENT INFORMATION - Narrative (Details)	12 Months Ended
SEGMENT INFORMATION - Narrative (Details)	Dec. 31, 2025 segment
Segment Reporting [Abstract]
Number of operating segments	1
Number of reportable segments	1

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - Equity Plans (Details) - shares	Dec. 31, 2025	Jun. 10, 2025	Dec. 31, 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding (in shares)	18,152,258		16,684,325
Inducement Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding (in shares)	1,152,477
Keryx Equity Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards outstanding (in shares)	148,860		163,765
Additional awards authorized for grant (in shares)	0		0
Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (the 2014 Plan)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards outstanding (in shares)	8,412,898		11,559,708
Additional awards authorized for grant (in shares)	0		0
Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (the 2014 Plan) \| Inducement Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding (in shares)	1,050,525		1,151,127
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan), as amended
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards outstanding (in shares)	15,913,729		10,390,642
Additional awards authorized for grant (in shares)	24,723,655		11,340,648
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan), as amended \| Inducement Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional awards authorized for grant (in shares)		18,900,000
Number of options outstanding (in shares)	3,034,085		2,534,775

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
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-Subparagraph (d)(1)
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Estimated Useful Lives for Property, Plant and Equipment (Details)	Dec. 31, 2025
Computer equipment and software
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Furniture and fixtures \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Furniture and fixtures \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Laboratory and other equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years

LICENSE, COLLABORATION AND OTHER REVENUE - TPC Collaboration Agreement - Narrative (Details)		1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 11, 2015 USD ($) performance_obligation	Jun. 30, 2013 USD ($) performance_obligation	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues					$ 236,196,000	$ 160,180,000	$ 194,623,000
Accounts receivable, net					47,031,000	34,368,000
Payables					21,185,000	15,180,000
Revenue recognized					0	0	3,738,000
Tanabe Pharma Corporation \| License Collaboration And Other Revenue, Royalties
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 8,700,000				1,800,000	1,900,000	2,000,000.0
Tanabe Pharma Corporation \| Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue	$ 25,000,000.0				25,000,000.0
Total revenues			$ 15,000,000.0	$ 10,000,000.0
Tanabe Pharma Corporation \| Development And Commercialize Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, expiration period	10 years
Termination of agreement by counterparty, written notice period (in months)	12 months
Number of performance obligations \| performance_obligation	2
Tanabe Pharma Corporation \| Development And Commercialize Collaboration Agreement \| Development Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue	$ 10,000,000.0
Tanabe Pharma Corporation \| Development And Commercialize Collaboration Agreement \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalty payments on sales	20.00%
Tanabe Pharma Corporation \| Development And Commercialize Collaboration Agreement \| Maximum \| Development, Regulatory and Commercial Events
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone revenue	$ 225,000,000.0
Tanabe Pharma Corporation \| Development And Commercialize Collaboration Agreement \| Maximum \| Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible milestone payments (up to)	40,000,000.0
Tanabe Pharma Corporation \| Development And Commercialize Collaboration Agreement \| Maximum \| Commercial Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone revenue (up to)	$ 175,000,000.0
Tanabe Pharma Corporation \| Development And Commercialize Collaboration Agreement \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalty payments on sales	13.00%
Tanabe Pharma Corporation \| Development And Commercialize Research And License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue	$ 10,000,000.0
Upfront cash payment received	20,000,000.0
Incurred clinical and commercial development cost	20,500,000
Cost of research services	$ 20,500,000
Accounts receivable, net					0
Deferred revenue					0
Payables					0
Contact asset					500,000
Tanabe Pharma Corporation \| Mitsubishi Tanabe Pharma Corporation Supply Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable, net					0
Deferred revenue					0
Revenue recognized					1,000,000.0	700,000	3,700,000
Other current liabilities					0
JT and Torii \| Sublicense Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues					5,700,000	5,400,000	5,400,000
Number of performance obligations \| performance_obligation		2
Accounts receivable, net					1,500,000
Potential payment for achievement of annual net sales milestones		$ 55,000,000.0
License agreement, notice period for termination		6 months
Prior written notice for termination on the breach of agreement period		60 days
Medice \| License Collaboration And Other Revenue, Royalties
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues					100,000	0	0
Medice \| Amended Supply Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues					0	0	0
Medice \| Supply Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues					300,000	$ 0	$ 0
Accounts receivable, net					300,000
Deferred revenue					0
Payables					$ 0

NATURE OF BUSINESS	12 Months Ended
NATURE OF BUSINESS	Dec. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS	NATURE OF BUSINESS Organization Akebia Therapeutics, Inc., referred to as Akebia or the Company, was incorporated in the State of Delaware in 2007 and became a public company in 2014. Akebia is a fully integrated commercial-stage biopharmaceutical company focused on developing and commercializing innovative therapeutics. The Company has two products approved by the Food and Drug Administration, or FDA, in the United States, or U.S. Vafseo® (vadadustat) is an oral hypoxia-inducible factor prolyl hydroxylase, or HIF-PH, inhibitor. Vafseo (vadadustat) Tablets were approved in the U.S. in March 2024 for the treatment of anemia due to chronic kidney disease, or CKD, in adults who have been receiving dialysis for at least three months. Vafseo entered the U.S. market in January 2025. Auryxia® (ferric citrate) is an orally administered medicine approved and marketed in the U.S. for two indications: (i) the control of serum phosphorus levels in adult patients with dialysis dependent chronic kidney disease, or DD-CKD, and (ii) the treatment of iron deficiency anemia, or IDA, in adult patients with non-dialysis dependent chronic kidney disease, or NDD-CKD. Auryxia lost exclusivity in the U.S. in March 2025. Vafseo is also approved for the treatment of symptomatic anemia associated with CKD in the European Economic Area, or EEA, the United Kingdom, or the UK, Switzerland, Australia, South Korea and Taiwan in adult patients on chronic maintenance dialysis and in Japan for adult dialysis-dependent and non-dialysis patients. Vafseo is marketed and sold by the Company's collaboration partners in certain countries. Ferric citrate is also approved in Japan, and is marketed and sold by the Company's collaboration partner, as an oral treatment for the improvement of hyperphosphatemia in patients with CKD, including DD-CKD and NDD-CKD, and for the treatment of adult patients with IDA under the trade name Riona (ferric citrate hydrate). Since its inception, the Company has devoted most of its resources to research and development, or R&D, including its preclinical and clinical development activities, commercializing Auryxia and Vafseo and providing general and administrative support for these operations. The Company's mid-stage rare kidney disease pipeline assets, praliciguat and AKB-097, are being evaluated to target areas of unmet need. The Company's early-stage pipeline assets include AKB-9090 and AKB-10108, which are HIF molecules. In addition, the Company continues to explore additional development opportunities to expand its pipeline and portfolio of novel therapeutics through both internal research and external innovation to leverage its fully integrated team. As of December 31, 2025, the Company had cash and cash equivalents of approximately $184.8 million. Based on its current operating plan, the Company believes that its cash resources and the cash the Company expects to generate from product, royalty, supply and license revenues will be sufficient to fund its current operating plan through at least twelve months from the filing of this Annual Report on Form 10-K, or Form 10-K. However, if the Company’s operating performance deteriorates significantly from the levels expected in the Company’s operating plan, including if the Company does not achieve its future anticipated Vafseo revenue projections, it would affect the Company’s liquidity and its ability to continue as a going concern in the future. The Company expects to finance future cash needs through product and license, collaboration and other revenue, including royalties and revenue from supply agreements. In addition, the Company may seek to sell public or private equity, enter into new debt transactions, explore potential strategic transactions, consider other cash-generating or saving measures or a combination of these approaches or other strategic alternatives. There can be no assurance that the current operating plan will be achieved in the time frame anticipated by the Company or that its cash resources will fund its operating plan for the period of time anticipated by the Company, or that additional funding will be available on terms acceptable to the Company, or at all.

ADDITIONAL BALANCE SHEET DETAIL - Schedule of Other Long-Term Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Payables and Accruals [Abstract]
Long-term inventories	$ 59,129	$ 34,953
Restricted cash	0	1,680
Other	552	744
Other long-term assets	$ 59,681	$ 37,377

PRODUCT REVENUE AND PROVISIONS FOR VARIABLE CONSIDERATION

12 Months Ended

Dec. 31, 2025

Revenue from Contract with Customer [Abstract]

PRODUCT REVENUE AND PROVISIONS FOR VARIABLE CONSIDERATION

Until Vafseo's market entry in January 2025, the Company’s only source of product revenue was from the U.S. sales of Auryxia. The following table presents net product revenue for Vafseo and Auryxia (in thousands):


	Years Ended December 31,
Product	2025		2024		2023
Vafseo	$	45,790	$	—	$	—
Auryxia(1)	181,542		152,180		170,301
Total product revenues	$	227,332	$	152,180	$	170,301

(1) Includes the authorized generic version of Auryxia sold and distributed by the Company's authorized generic distribution partner, Mylan Therapeutics, Inc., or AG Distributor, during the year ended December 31, 2025.

The following table presents changes in the Company’s contract assets and liabilities related to the Company's sales to its AG Distributor (in thousands):


	Year Ended December 31, 2025
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable	$	—	$	12,006	$	(11,812)	$	194
Contract liabilities:
Deferred revenue	$	—	$	10,675	$	(7,994)	$	2,681

Product revenue allowance and provision categories were as follows:


(in thousands)	Chargebacks and Discounts		Rebates, Fees and other Deductions		Returns		Total
Balance at December 31, 2022	$	1,259	$	26,252	$	10,923	$	38,434
Provisions related to sales in current year	11,138		79,648		6,181		$	96,967
Adjustments related to prior year sales	(304)		(1,506)		1,648		$	(162)
Credits/payments made	(10,486)		(81,403)		(11,836)		$	(103,725)
Balance at December 31, 2023	$	1,607	$	22,991	$	6,916	$	31,514
Current provisions related to sales in current year	9,225		44,914		4,862		59,001
Adjustments related to prior year sales	(94)		(2,056)		(540)		(2,690)
Credits/payments made	(9,302)		(50,123)		(4,796)		(64,221)
Balance at December 31, 2024	$	1,436	$	15,726	$	6,442	$	23,604
Current provisions related to sales in current year	4,051		81,019		634		85,704
Adjustments related to prior year sales	69		143		(1,631)		(1,419)
Credits/payments made	(4,403)		(24,299)		(2,094)		(30,796)
Balance at December 31, 2025	$	1,153	$	72,589	$	3,351	$	77,093

Chargebacks, discounts and estimated product returns are recorded as a reduction of revenue in the period the related product revenue is recognized in the consolidated statements of operations and comprehensive loss. Chargebacks are recorded as a reduction to accounts receivable while discounts, rebates, fees and other deductions are recorded with a corresponding increase to accrued expenses and other current liabilities or accounts payable in the consolidated balance sheets. Estimated product returns on product sales that are not expected to be returned within one year are recorded as other long-term liabilities in the consolidated balance sheets.

Accounts receivable, net related to product sales was approximately $44.4 million and $32.4 million as of December 31, 2025 and 2024, respectively.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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-URI https://asc.fasb.org/1943274/2147479806/606-10-50-9

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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-Section 50
-Paragraph 12
-Subparagraph (c)
-Publisher FASB
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 12
-Subparagraph (d)
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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-Paragraph 12
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-Publisher FASB
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
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+ Details

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2025	Dec. 31, 2024
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Preferred stock, authorized (in shares)	25,000,000	25,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, authorized (in shares)	350,000,000	350,000,000
Common stock, issued (in shares)	265,424,818	224,848,992
Common stock, outstanding (in shares)	265,424,818	224,848,992

LIABILITY RELATED TO SETTLEMENT ROYALTIES, WORKING CAPITAL FUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES (Tables)

12 Months Ended

Dec. 31, 2025

Other Liabilities Disclosure [Abstract]

Schedule of Liability Related to Sale of Future Royalties

As of December 31, 2025 and 2024, the balances related to the settlement royalties liability were as follows (in thousands):


	December 31,
Description	2025		2024
Current portion (included in accrued expenses and other current liabilities)	$	12,516	$	5,924
Long-term portion	54,750		46,697
Total settlement royalties liability	$	67,266	$	52,621

As of December 31, 2025 and 2024, the balances related to the Working Capital Fund liability were as follows (in thousands):


	December 31,
Description	2025		2024
Current portion	$	17,356	$	2,274
Long-term portion	22,606		38,013
Total Working Capital Fund liability	$	39,962	$	40,287

As of December 31, 2025 and 2024, the balances related to the liability related to the sale of future royalties were as follows (in thousands):


	December 31,
Description	2025		2024
Current portion (included in accrued expenses and other current liabilities)	$	1,664	$	2,039
Long-term portion	50,608		52,066
Total liability related to sale of future royalties	$	52,272	$	54,105

INDEBTEDNESS

12 Months Ended

Dec. 31, 2025

Debt Disclosure [Abstract]

INDEBTEDNESS

Entry into BlackRock Loan Facility

On January 29, 2024, or the Closing Date, the Company entered into the Agreement for the Provision of a Loan Facility, or the BlackRock Credit Agreement, with Kreos Capital VII (UK) Limited, or Kreos, which are funds and accounts managed by BlackRock Inc., collectively, BlackRock, and provides for a senior secured term loan facility in the aggregate principal amount of up to $55.0 million, or the Term Loan Facility. The Term Loan Facility was available in three tranches: (i) Tranche A — $37.0 million was funded on the Closing Date and used to repay the Pharmakon Term Loans (as defined below); (ii) Tranche B — $8.0 million was funded on April 19, 2024, or the Tranche B Closing Date; and (iii) Tranche C — $10.0 million was funded on February 3, 2025, or the Tranche C Closing Date, collectively the Term Loans.

On February 3, 2025, the Company and Kreos entered into a Second Amendment to the BlackRock Credit Agreement, or the Second Amendment, which, among other things, extended the expiry date of Tranche C from December 31, 2024 to the Tranche C Closing Date, or the Extended Tranche C. Tranche C was available subject to receipt of a certain amount of cumulative gross cash proceeds after the Closing Date in the form of equity or equity linked securities in one or more series of transactions. The terms of the Extended Tranche C are substantially similar to the terms of the original Tranche C, however, interest accrued on the Extended Tranche C as if it was advanced on December 31, 2024.

On the Closing Date, the Company received $34.5 million on Tranche A, after deducting debt issuance costs, fees and expenses. On the Tranche B Closing Date, the Company received $7.5 million, after deducting debt issuance costs, fees and expenses. On the Tranche C Closing Date, the Company received $9.3 million, after deducting debt issuance costs, interest, fees and expenses.

The BlackRock Term Loan Facility had an initial maturity date of March 31, 2025, which was automatically extended to January 29, 2028, after the Company received FDA approval for Vafseo, or the BlackRock Maturity Date. The Company is required to make interest-only payments until December 31, 2026, or the BlackRock Interest Only Period, after which the Company will begin paying equal monthly principal on the first calendar day of each month. In the event of certain prespecified events, the repayment schedule will be accelerated.

The Term Loan Facility will accrue interest at a floating annual rate equal to the sum of (i) the term Secured Overnight Financing Rate, or SOFR, for a tenor of one month (subject to a floor of 4.25% per annum) plus (ii) a margin of 6.75% per annum (subject to an overall cap of 15.00% per annum on the all-in interest rate). As of December 31, 2025, the Company's interest rate was 11.00%. During the years ended December 31, 2025 and 2024, the Company recognized interest expense of $8.4 million and $7.1 million, respectively.

During the continuance of any payment event of default under the BlackRock Credit Agreement, the interest rate on such overdue sum will automatically increase by an additional 3.0% per annum, and may be subject to an additional late fee of

2.0% of such overdue sum. The Term Loan Facility also includes transaction fees ranging from 1.00% to 1.25% of the draw down amount as well as exit fees of 0.75% of the amount funded to the relevant tranche.

If the Company prepays the outstanding loan prior to maturity, it will be required to pay a prepayment fee ranging from 1.0% to 4.0% of the amount prepaid.

As of December 31, 2025, future principal payments under the BlackRock Credit Agreement are as follows (in thousands):


Years ended December 31,	Amounts


2026	—
2027	50,558
2028	1,881
Total before unamortized discount and issuance costs	52,439
Less: unamortized discount and issuance costs	(4,189)
Total term loans	$	48,250

The BlackRock Term Loan Facility is secured by substantially all of the existing and after-acquired assets of the Company, including intellectual property. The BlackRock Credit Agreement requires the Company to (i) maintain a minimum aggregate cash balance of $15.0 million in one or more controlled accounts or (ii) trailing twelve-month revenue of $150.0 million, both of which are measured monthly. The BlackRock Credit Agreement contains certain representations and warranties, affirmative and negative covenants that limit the Company's ability to engage in specified types of transactions and other provisions typical within a credit agreement. If an event of default occurs and is continuing under the BlackRock Credit Agreement, BlackRock is entitled to take enforcement action, including acceleration of amounts due and it could limit the Company's ability to make certain payments under the Vifor Termination Agreement (as defined below).

On July 10, 2024, in connection with the Termination and Settlement Agreement entered into between the Company and CSL Vifor (as defined below), or the Vifor Termination Agreement, the Company and Kreos entered into a First Amendment to the BlackRock Credit Agreement, which amended certain provisions of the BlackRock Credit Agreement. See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for further information on the Vifor Termination Agreement.

Warrant

On the Closing Date, Kreos Capital VII Aggregator SCSp, an affiliate of Kreos, or the Warrant Holder, received a warrant to purchase 3,076,923 shares of the Company’s common stock, at an exercise price per share of $1.30, or the Initial Warrant. On the Tranche C Closing Date, the Company issued the Warrant Holder an additional warrant to purchase 1,153,846 shares of the Company’s common stock at an exercise price per share of $1.30, or the Tranche C Warrant. Each warrant is exercisable for eight years from the date of issuance.

On July 21, 2025, the Warrant Holder exercised its option to purchase 2,115,384 shares of the Company's common stock under the Initial Warrant on a cashless basis at an exercise price per share of $1.30. A cashless exercise allows the Warrant Holder to convert the warrants into shares of the Company's common stock without the need for a cash payment. Instead of paying cash upon exercise, the Warrant Holder received a reduced number of shares based on a predetermined formula. On July 23, 2025, as a result of the cashless exercise, the Company issued 1,408,588 shares of common stock to the Warrant Holder under the Initial Warrant.

The Initial Warrant and the Tranche C Warrant are liabilities classified under ASC 815, Derivatives and Hedging, as they could potentially require net cash settlement outside of the Company’s control. The Initial Warrant and the Tranche C Warrant are measured at fair value each reporting period and when a warrant is exercised, with the changes in fair value presented within the consolidated statements of operations and comprehensive loss. The fair value of the warrant liability was $3.0 million and $5.2 million as of December 31, 2025 and 2024, respectively. See Note 3, Fair Value of Financial Instruments, for information on the fair value determination.

Other Agreements Accounted for as Debt

The Company has a liability related to settlement royalties and a Working Capital Fund liability with Vifor (International) Ltd. (now a part of CSL Limited), or CSL Vifor, and a liability related to the sale of future royalties, which are accounted for as debt arrangements. See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for further information.

Pharmakon Term Loan (Extinguished January 29, 2024)

On November 11, 2019, the Company, with Keryx as guarantor, entered into a loan agreement, or Pharmakon Loan Agreement, which consisted of a secured term loan facility in an aggregate amount of up to $100.0 million, or Pharmakon Term Loans.

On the Closing Date, using the proceeds from the BlackRock Credit Agreement, the Company paid the then outstanding principal balance on the Pharmakon Term Loans of $35.0 million, plus the outstanding interest and a prepayment fee of $0.2 million. During the year ended December 31, 2024, the Company recorded a debt extinguishment loss of $0.5 million.

The Company recognized immaterial interest expense and $6.0 million of interest expense related to the Pharmakon Loan Agreement during the years ended December 31, 2024 and 2023, respectively.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Dec. 31, 2025
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Manufacturing and Unconditional Purchase Commitment Agreements Siegfried Manufacturing The Company's contractual obligations include a commercial supply agreement with Siegfried Evionnaz, or Siegfried, to supply commercial drug substance for Auryxia. The Company and Siegfried entered into a Master Manufacturing Services and Supply Agreement, most recently amended in February 2023, or the Siegfried Agreement, under which the Company has agreed to purchase a minimum quantity of drug substance of Auryxia, annually at a predetermined price. As of December 31, 2025, the Company had a minimum total commitment of approximately $0.8 million through the end of 2026. The term of the Siegfried Agreement expires on December 31, 2026. The Siegfried Agreement provides the Company and Siegfried with certain early termination rights. The Company regularly reviews its estimate of the excess firm purchase commitment liability which relates to the amount of minimum purchase commitments under the Siegfried Agreement that exceed the current forecast, including review of assumptions of expected future demand and expiry of inventory. The excess firm purchase commitment liability was $0.8 million and $3.6 million as of December 31, 2025 and 2024, respectively. The Company did not record a charge to cost of product and other revenue related to the change in the excess firm purchase commitment liability during the year ended December 31, 2025. During the years ended December 31, 2024 and 2023, the Company recorded $2.1 million and $1.5 million, respectively, to costs of product and other revenue related to the change in the excess firm purchase commitment liability. Patheon Manufacturing In March 2020, the Company entered into a Supply Agreement with Patheon Inc., or Patheon, or the Patheon Agreement, under which Patheon agreed to manufacture Vafseo drug product for commercial use under a volume-based pricing structure through June 30, 2023, with the agreement renewing annually unless either party gives the other party eighteen months' prior written notice. Under the Patheon Agreement, the Company agreed to purchase from Patheon a certain percentage of the estimated global demand for Vafseo drug product based on certain quarterly and annual forecasts provided by the Company. As of December 31, 2025, the Company has committed to purchase $1.1 million of Vafseo drug product from Patheon through the end of 2026, however, as estimated global demand fluctuates, the Company may have additional future obligations under the Patheon Agreement. WuXi STA Manufacturing In April 2020, the Company entered into a Supply Agreement with STA Pharmaceutical Hong Kong Limited, a subsidiary of WuXi AppTec, or WuXi STA, or, as amended, the WuXi STA DS Agreement. Under the WuXi STA DS Agreement, WuXi STA will manufacture Vafseo drug substance for commercial use under a volume-based pricing structure through April 2, 2029. Pursuant to the WuXi STA DS Agreement, the Company has agreed to purchase a certain percentage of the global demand for Vafseo drug substance from WuXi STA. As of December 31, 2025, the Company has committed to purchase $69.2 million of Vafseo drug substance from WuXi STA through the end of 2027, however, as estimated global demand fluctuates, the Company may have additional future obligations under the WuXi STA DS Agreement. On February 10, 2021, the Company entered into a Supply Agreement with WuXi STA, which was amended on October 15, 2024, or the WuXi STA DP Agreement, under which WuXi STA will manufacture and supply Vafseo drug product for commercial purposes under a volume-based pricing structure through January 1, 2032. The Vafseo drug product price is reviewed annually by the Company and WuXi STA. The Company also reimburses WuXi STA for certain reasonable expenses. Pursuant to the WuXi STA DP Agreement, the Company has agreed to purchase a certain percentage of global demand for Vafseo drug product from WuXi STA. The WuXi STA DP Agreement may be renewed or extended by mutual agreement of the Company and WuXi STA with at least eighteen months’ prior written notice. The WuXi STA DP Agreement allows the Company to terminate the relationship on 180 calendar days’ prior written notice to WuXi STA for any reason. In addition, each party has the ability to terminate the WuXi STA DP Agreement upon the occurrence of certain conditions. As of December 31, 2025, the Company has committed to purchase $1.8 million of Vafseo drug product from WuXi STA through the first half of 2026, however, as estimated global demand fluctuates, the Company may have additional future obligations under the WuXi STA DP Agreement. Esteve - Assigned Supply Agreement On April 9, 2019, the Company entered into a Supply Agreement with Esteve Química, S.A., or Esteve, or the Esteve Agreement, under which Esteve would manufacture Vafseo drug substance for commercial use under a volume-based pricing structure. On December 16, 2022, the Company, TPC and Esteve executed the Esteve Assignment Agreement, pursuant to which the Esteve Agreement was assigned to TPC. The Esteve Assignment Agreement transferred the rights and obligations of the Esteve Agreement to TPC, specifically including the obligations under certain purchase orders issued by the Company and accepted by Esteve. As of December 31, 2025, the Company has no minimum commitments with Esteve, however, the Company may have future obligations with Esteve. BioVectra - Former Manufacturing and Unconditional Purchase Commitments Under the Manufacture and Supply Agreement with BioVectra, Inc., or BioVectra, and the Amended and Restated Product Manufacture and Supply and Facility Construction Agreement with BioVectra, the Company agreed to purchase minimum quantities of Auryxia drug substance annually at predetermined prices as well as reimburse BioVectra for certain costs in connection with construction of a new facility for the manufacture and supply of Auryxia drug substance. On December 22, 2022, the Company and BioVectra entered into a termination agreement, or the BioVectra Termination Agreement, pursuant to which the parties agreed, among other things, to terminate, effective immediately, any and all existing agreements entered into between the parties in connection with the manufacture and supply, by BioVectra to the Company, of Auryxia drug substance. Under the terms of the BioVectra Termination Agreement, each of the Company and BioVectra released one another from all existing and future claims and liabilities and the return of certain materials and documents. In addition, the Company agreed to pay BioVectra a total of $32.5 million consisting of (i) an upfront payment of $17.5 million and (ii) six quarterly payments of $2.5 million which commenced in April 2024 and were completed in July 2025, totaling $15.0 million. The upfront payment of $17.5 million was made during the quarter ended December 31, 2022 and was recorded in cost of product and other revenue. In accordance with ASC 420, Exit or Disposal Cost Obligations, the Company recognized a liability and corresponding expense for the remaining termination fees based on estimated fair value as of December 22, 2022. The Company imputed interest on the liability for the remaining termination fees at a rate of 17.0% per annum, which was determined based on certain factors, including the Company's credit rating, comparable securities yield and expected repayment period of the remaining termination fees. The Company recorded an initial discount on the remaining termination fees in the consolidated balance sheet on the date of the termination. This resulted in the recording of a liability and corresponding charge to cost of goods sold of $11.2 million during the quarter ended December 31, 2022. The discount on the liability balance was amortized to interest expense using the effective interest rate method over the term of the liability. The amortization of the discount was $0.3 million, $1.6 million and $1.9 million for the years ended December 31, 2025, 2024 and 2023, respectively. License Agreements Panion License Agreement On April 17, 2019, the Company and Panion & BF Biotech, Inc., or Panion, entered into a second amended and restated license agreement, or Panion Amended License Agreement, which amended and restated in full the license agreement between the Company and Panion. The Panion Amended License Agreement provides the Company with an exclusive license under Panion-owned know-how and patents covering the rights to sublicense, develop, make, use, sell, offer for sale, import and export ferric citrate worldwide, excluding certain Asian-Pacific countries, or the Licensor Territory. The Panion Amended License Agreement also provides Panion with an exclusive license under Company-owned patents covering the rights to sublicense (with the Company’s written consent), develop, make, use, sell, offer for sale, import and export ferric citrate in certain countries in the Licensor Territory. Under the Panion Amended License Agreement, Panion is eligible to receive from the Company or any sublicensee royalty payments based on a mid-single digit percentage of sales of ferric citrate in the Company’s licensed territories. The Company is eligible to receive from Panion or any sublicensee royalty payments based on a mid-single digit percentage of net sales of ferric citrate in Panion’s licensed territories. The Panion Amended License Agreement terminates upon the expiration of each of the Company’s and Panion’s obligations to pay royalties thereunder. In addition, the Company may terminate the Panion Amended License Agreement (i) in its entirety or (ii) with respect to one or more countries in the Company’s licensed territory, in either case upon ninety days’ notice. The Company and Panion also each have the right to terminate the Panion Amended License Agreement upon the occurrence of a material breach of the Panion Amended License Agreement by the other party, subject to certain cure provisions, or certain insolvency events. The Panion Amended License Agreement also provides that, on a country-by-country basis, until the second anniversary of the expiration of the obligation of the Company or Panion, as applicable, to pay royalties in a country in which such party has ferric citrate for sale on the date of such expiration, neither the other party nor its affiliates will, directly or indirectly, sell, distribute or otherwise commercialize or supply or cause to supply ferric citrate to a third party for sale or distribution in such country. The Panion Amended License Agreement includes customary terms relating to, among others, indemnification, confidentiality, remedies, and representations and warranties. In addition, the Panion Amended License Agreement provides that each of the Company and Panion has the right, but not the obligation, to conduct litigation against any infringer of certain patent rights under the Panion Amended License Agreement in certain territories. During the years ended December 31, 2025, 2024 and 2023, the Company incurred approximately $11.3 million, $9.1 million and $10.0 million, respectively, in royalty payments due to Panion relating to the Company’s sales of Auryxia in the U.S. and Japan Tobacco, Inc. and its subsidiary Torii Pharmaceutical Co., Ltd., collectively, JT and Torii’s, net sales of Riona in Japan. Cyclerion Agreement In June 2021, the Company entered into a license agreement, or the Cyclerion Agreement, with Cyclerion Therapeutics Inc., or Cyclerion, under which the Company obtained an exclusive global license under certain intellectual property rights to research, develop and commercialize praliciguat, an investigational oral soluble guanylate cyclase stimulator. Under the terms of the Cyclerion Agreement, the Company made an upfront payment of $3.0 million to Cyclerion, which was paid during the second quarter of 2021. Substantially all of the fair value of the assets acquired in conjunction with the Cyclerion Agreement was concentrated in the acquired license. As a result, the Company accounted for this transaction as an asset acquisition under ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. The $3.0 million upfront payment was charged to research and development expense at acquisition in June of 2021, as it relates to a development stage compound with no alternative future use. In December 2024, the Company and Cyclerion entered into Amendment #1 to the Cyclerion Agreement, pursuant to which the Company agreed to pay Cyclerion (i) $1.25 million, which was paid in December 2024, and (ii) $0.5 million, which was paid in September 2025. In addition, the parties agreed to the reduction of certain development milestones and the increase of certain royalty rates on net sales and sublicense income. During the year ended December 31, 2024, the Company recorded the $1.25 million payment and $0.5 million payment to research and development expense in accordance with ASC 730, Research and Development, as praliciguat remains a development stage compound with no alternative future use. Furthermore, the only contingency as it related to the $0.5 million payment made in September 2025 was the passage of time. Under the Cyclerion Agreement, as amended, Cyclerion is eligible to receive up to an additional aggregate of $197.5 million from the Company in specified development and regulatory milestone payments on a product-by-product basis. In December 2025, the Company incurred a $1.0 million development milestone in connection with the initiation of a Phase 2 clinical trial for praliciguat in the U.S., which was charged to research and development expense during the year ended December 31, 2025. The $1.0 million development milestone payment is included in accrued expenses and other current liabilities in the accompanying consolidated balance sheet as of December 31, 2025. Cyclerion will also be eligible to receive specified commercial milestones as well as tiered royalties ranging from a mid-single-digit percentage to twenty percent of net sales, on a product-by-product basis, and subject to reduction upon expiration of patent rights or the launch of a generic product in the territory. Unless earlier terminated, the Cyclerion Agreement will expire on a product-by-product and country-by-country basis upon the expiration of the last royalty term, which ends upon the longest of (i) the expiration of the patents licensed under the Cyclerion Agreement, (ii) the expiration of regulatory exclusivity for such product and (iii) ten years from first commercial sale of such product. The Company may terminate the Cyclerion Agreement in its entirety or only with respect to a particular licensed compound or product upon 180 days' prior written notice to Cyclerion. The parties also have customary termination rights, subject to a cure period, in the event of the other party’s material breach of the Cyclerion Agreement or in the event of certain additional circumstances. Q32 Agreement On November 28, 2025, or the APA Closing Date, the Company entered into an Asset Purchase Agreement, or the Q32 Purchase Agreement, with Q32 Bio Inc. and Q32 Bio Operations Inc, or together, Q32, pursuant to which Q32 sold and assigned to the Company, and the Company purchased and assumed from Q32 substantially all assets and liabilities of Q32 and its affiliates related to the research, development, manufacture and commercialization of Q32's clinical-stage development candidate known as ADX-097 (now referred to as AKB-097) worldwide for the treatment, prevention or diagnosis of any disease or condition in humans. AKB-097, which has been evaluated in a Phase 1 clinical trial in healthy volunteers, is a tissue-targeted C3d-Factor H fusion protein complement inhibitor with the potential to treat rare kidney diseases. Under the terms of the Q32 Purchase Agreement, the Company (i) made an upfront payment of $7.0 million on the APA Closing Date, (ii) will make an additional upfront payment of $3.0 million on the six-month anniversary of the APA Closing Date, (iii) will make certain milestone payments upon the achievement of specified development and regulatory milestone events related to AKB-097 up to an aggregate amount equal to $94.5 million, including a $2.0 million development milestone payment upon the earlier of initiation of a Phase 2 clinical trial and December 31, 2026, (iv) will make certain milestone payments upon the achievement of specified commercial milestone events with respect to the net sales of AKB-097 up to an aggregate amount equal to $487.5 million, and (v) will make certain royalty payments based on the net sales of AKB-097 with royalty percentage tiers ranging from the low single digits to mid-teen percentages. The royalties will expire on a country-by-country basis on the later to occur of (a) the date of expiration of the last-to-expire valid claim of any transferred patent right that covers such product in such country, and (b) the tenth anniversary of the first commercial sale of such product. The transaction was accounted for as an asset acquisition as the acquired assets did not meet the definition of a business. The Company did not acquire any outputs and there was not an acquired substantive process in place to create outputs. The total purchase consideration of $12.8 million was composed of the $7.0 million upfront payment, the $3.0 million additional upfront payment, the $2.0 million development milestone payment and $0.8 million of direct transaction costs. The only contingency as it relates to the $2.0 million milestone payment upon the earlier of initiation of a Phase 2 clinical trial and December 31, 2026 is the passage of time. The fair value was allocated to IPR&D assets with no alternative future use for these assets at the closing of the acquisition. As a result, the Company recorded a charge of $12.8 million related to acquired IPR&D expense on the consolidated statements of operations and comprehensive loss during the year ended December 31, 2025. The $3.0 million additional upfront payment and the $2.0 million development milestone payment are included in accrued expenses and other current liabilities in the consolidated balance sheet as of December 31, 2025. Other Third Party Contracts The Company contracts with various organizations to conduct R&D activities with remaining contract costs to the Company of approximately $82.6 million at December 31, 2025. The scope of the services under these R&D contracts can be modified upon mutual agreement of the parties, and the contracts or scope of services can be cancelled by the Company upon written notice. In some instances, the contracts may be cancelled by the third party upon written notice. Litigation and Related Matters The Company is involved from time to time in various legal proceedings arising in the normal course of business. The Company provides disclosure when a loss in excess of any reserve is reasonably possible, and if estimable, the Company discloses the potential loss or range of possible loss. Significant judgment is required to assess the likelihood of various potential outcomes and the quantification of loss in those scenarios. Changes in the Company’s estimates could have a material impact and are recorded as litigation progresses and new information comes to light. Although the outcomes of potential legal proceedings are inherently difficult to predict, the Company does not expect the resolution of current legal proceedings to have a material adverse effect on its financial position, results of operations or cash flows of the Company. Guarantees and Indemnifications As permitted under Delaware law, the Company may indemnify its officers, directors and employees for certain events or occurrences that happen by reason of their relationship with, or position held at, the Company. The Company may also be subject to indemnification obligations by law with respect to the actions of its employees under certain circumstances and in certain jurisdictions. The Company maintains director and officer liability insurance coverage that is intended to cover a portion of amounts that may be due with respect to indemnification after a deductible is met. Further, the Company is a party to a variety of agreements in the ordinary course of business under which it may be obligated to indemnify third parties with respect to certain matters. For the years ended December 31, 2025, 2024 and 2023, the Company did not experience any losses related to these indemnification obligations, and no claims were outstanding as of December 31, 2025. The Company does not have any claims related to these indemnification obligations and consequently concluded that the fair value of these obligations is negligible and no related accruals were recorded.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2025

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash

The following table reconciles cash, cash equivalents and restricted cash reported within the Company's consolidated balance sheets to the total amounts reported in the consolidated statements of cash flows:


	December 31,
Reconciliation of cash, cash equivalents and restricted cash (in thousands)	2025		2024		2023
Cash and cash equivalents	$	184,844	$	51,870	$	42,925
Restricted cash	1,699		1,680		1,654
Total cash, cash equivalents and restricted cash	$	186,543	$	53,550	$	44,579

Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash


	December 31,
Reconciliation of cash, cash equivalents and restricted cash (in thousands)	2025		2024		2023
Cash and cash equivalents	$	184,844	$	51,870	$	42,925
Restricted cash	1,699		1,680		1,654
Total cash, cash equivalents and restricted cash	$	186,543	$	53,550	$	44,579

Schedule of Allowance for Credit Losses

The following table summarizes the activity related to the Company's allowance for credit losses (in thousands):


	Year Ended December 31,
	2025		2024		2023
Beginning balance	$	1,212	$	1,029	$	1,106
Provision for bad debts	1,479		877		(77)
Recoveries/(write-offs)	—		(695)		—
Ending balance	$	2,691	$	1,212	$	1,029

Schedule of Revenue and Gross Accounts Receivable By Major Customer

Gross revenues and accounts receivable from each of the Company’s customers or collaboration partners who individually accounted for 10% or more of total gross revenues and/or 10% or more of total gross accounts receivable consisted of the following:


	% of Total Gross Revenues
	Years Ended December 31,
Customer	2025	2024	2023
Fresenius Medical Care Rx	30%	48%	40%
U.S. Renal Care	29%	*	*
DaVita, Inc.	25%	*	*
Cencora, Inc.	*	19%	21%
McKesson Corporation	*	12%	11%
Cardinal Health, Inc.	*	*	10%


	% of Gross Accounts Receivable
	December 31,
Customer	2025	2024
U.S. Renal Care	42%	*
DaVita, Inc.	29%	16%
Fresenius Medical Care Rx	*	42%
Cencora, Inc.	*	13%

*Percentage less than 10% threshold.

Schedule of Estimated Useful Lives for Property, Plant and Equipment

Depreciation expense is recognized using the straight-line method over the estimated useful lives, which are typically:

Asset Category

Estimated Useful Life

Computer equipment and software

3 years

Furniture and fixtures

5 years

7 years

Laboratory and other equipment

7 years

Leasehold improvements

Shorter of the useful life or remaining lease term

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - RSU and PSU Activity (Details) - Restricted Stock Units (RSUs) And Performance Based Restricted Stock Units (PSUs)	12 Months Ended
	Dec. 31, 2025 $ / shares shares
2014 Stock Incentive Plan
Number of Shares
Outstanding beginning balance (in shares) \| shares	1,321,423
Granted (in shares) \| shares	0
Vested (in shares) \| shares	(849,701)
Forfeited and canceled (in shares) \| shares	(141,100)
Outstanding ending balance (in shares) \| shares	330,622
Weighted Average Grant Date Fair Value
Outstanding beginning balance, weighted average fair value (in dollars per share) \| $ / shares	$ 0.95
Granted, weighted average fair value (in dollars per share) \| $ / shares	0.00
Vested, weighted-average grant date fair value (in dollars per share) \| $ / shares	1.06
Forfeited and canceled, weighted average fair value (in dollars per share) \| $ / shares	0.98
Outstanding ending balance, weighted average fair value (in dollars per share) \| $ / shares	$ 0.63
2023 Stock Incentive Plan
Number of Shares
Outstanding beginning balance (in shares) \| shares	4,108,367
Granted (in shares) \| shares	4,492,000
Vested (in shares) \| shares	(1,636,898)
Forfeited and canceled (in shares) \| shares	(970,862)
Outstanding ending balance (in shares) \| shares	5,992,607
Weighted Average Grant Date Fair Value
Outstanding beginning balance, weighted average fair value (in dollars per share) \| $ / shares	$ 1.59
Granted, weighted average fair value (in dollars per share) \| $ / shares	2.31
Vested, weighted-average grant date fair value (in dollars per share) \| $ / shares	1.55
Forfeited and canceled, weighted average fair value (in dollars per share) \| $ / shares	1.89
Outstanding ending balance, weighted average fair value (in dollars per share) \| $ / shares	$ 2.09

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Dec. 31, 2025
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS The Company has evaluated events and transactions occurring after the balance sheet date through the filing date of this Form 10-K with the Securities and Exchange Commission, to ensure that the audited consolidated financial statements include appropriate disclosure of events both recognized in the accompanying consolidated financial statements as of December 31, 2025, and events which occurred subsequently but were not recognized in the consolidated financial statements. The Company has concluded that no subsequent events have occurred that require disclosure other than the following: Entry into New Lease Agreement On January 27, 2026, the Company entered into a lease agreement, or the Waltham Lease, with BP THIRD AVENUE LLC, a Delaware limited liability company, pursuant to which the Company will lease an aggregate of approximately 43,474 square feet, consisting of 28,518 square feet of office space, or the Office Premises, and 14,956 square feet of laboratory space, or Lab Premises, located in Waltham, Massachusetts. The Company intends to relocate its corporate headquarters to the Waltham Lease in September 2026. The Cambridge Lease expires on September 11, 2026. The Company’s annual rent for the Office Premises will start at $0.9 million and will increase at an additional $1.00 per square foot for each successive Rent Year (as defined in the Waltham Lease) until the end of the initial term. The Company’s annual rent for the Lab Premises will start at $1.0 million and will increase by approximately 3.0% for each successive Rent Year until the end of the initial term. The Waltham Lease requires a security deposit in the amount of $0.8 million in the form of an irrevocable letter of credit. In addition to rent, the Company is required to pay additional amounts for taxes, insurance, maintenance and other operating expenses.

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Line Items]
U.S. federal tax at statutory rate	21.00%	21.00%	21.00%
Current income tax expense (benefit)	$ 1,624	$ 0	$ 0
Deferred income tax expense (benefit)	0	0	0
Increase (decrease) in valuation allowance, deferred tax assets	5,800	22,500	4,700
Research and development tax credit carryforwards	7,726	6,152
Decrease in deferred tax asset	44,900
Income tax paid, state and local, after refund received	700	0	0
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	1,240,800	1,245,800	1,230,400
Net operating loss carryforwards indefinitely due to tax cut and jobs act	663,800
Research and development tax credit carryforwards	5,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	562,200	$ 584,300	$ 590,800
Research and development tax credit carryforwards	$ 3,400

INTANGIBLE ASSET AND GOODWILL (Details) - USD ($)	12 Months Ended
INTANGIBLE ASSET AND GOODWILL (Details) - USD ($)	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Estimated useful life (in years)	6 years
Amortization expense	$ 0	$ 36,042,000	$ 36,042,000
Goodwill	59,044,000	$ 59,044,000
Goodwill, accumulated impairment losses	$ 0

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets.

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- Definition

Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

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+ Details

NATURE OF BUSINESS (Details) $ in Thousands	Dec. 31, 2025 USD ($) product	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of commercial products \| product	2
Cash and cash equivalents \| $	$ 184,844	$ 51,870	$ 42,925

PRODUCT REVENUE AND PROVISIONS FOR VARIABLE CONSIDERATION (Tables)

12 Months Ended

Dec. 31, 2025

Revenue from Contract with Customer [Abstract]

Schedule of Product Revenues

The following table presents net product revenue for Vafseo and Auryxia (in thousands):


	Years Ended December 31,
Product	2025		2024		2023
Vafseo	$	45,790	$	—	$	—
Auryxia(1)	181,542		152,180		170,301
Total product revenues	$	227,332	$	152,180	$	170,301

Schedule of Changes in Contract Assets and Liabilities

The following table presents changes in the Company’s contract assets and liabilities related to the Company's sales to its AG Distributor (in thousands):


	Year Ended December 31, 2025
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable	$	—	$	12,006	$	(11,812)	$	194
Contract liabilities:
Deferred revenue	$	—	$	10,675	$	(7,994)	$	2,681

The following table presents changes in the Company’s contract assets and liabilities related to license, collaboration and other revenue agreements (in thousands):


	Year Ended December 31, 2025
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable(1)	$	2,010	$	8,894	$	(8,513)	$	2,391
Contract liability:
Deferred revenue	$	—	$	—	$	—	$	—

	Year Ended December 31, 2024
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable(1)	$	3,333	$	8,562	$	(9,885)	$	2,010
Contract liabilities:
Deferred revenue (long-term)(2)	$	43,296	$	—	$	(43,296)	$	—

(1)Excludes accounts receivable from product sales of Auryxia and Vafseo which are included in the accompanying consolidated balance sheets as of December 31, 2025 and 2024.

(2)See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for further information.

Schedule of Product Revenue Allowance and Provision Categories

Product revenue allowance and provision categories were as follows:


(in thousands)	Chargebacks and Discounts		Rebates, Fees and other Deductions		Returns		Total
Balance at December 31, 2022	$	1,259	$	26,252	$	10,923	$	38,434
Provisions related to sales in current year	11,138		79,648		6,181		$	96,967
Adjustments related to prior year sales	(304)		(1,506)		1,648		$	(162)
Credits/payments made	(10,486)		(81,403)		(11,836)		$	(103,725)
Balance at December 31, 2023	$	1,607	$	22,991	$	6,916	$	31,514
Current provisions related to sales in current year	9,225		44,914		4,862		59,001
Adjustments related to prior year sales	(94)		(2,056)		(540)		(2,690)
Credits/payments made	(9,302)		(50,123)		(4,796)		(64,221)
Balance at December 31, 2024	$	1,436	$	15,726	$	6,442	$	23,604
Current provisions related to sales in current year	4,051		81,019		634		85,704
Adjustments related to prior year sales	69		143		(1,631)		(1,419)
Credits/payments made	(4,403)		(24,299)		(2,094)		(30,796)
Balance at December 31, 2025	$	1,153	$	72,589	$	3,351	$	77,093

INVENTORIES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
INVENTORIES - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Inventory [Line Items]
Write-down of inventory	$ 2,505	$ 4,208	$ 1,580
Benefit in cost of goods sold related to previously written down as excess inventory		12,300	4,300
Auryxia Drug Substance
Inventory [Line Items]
Write-down of inventory	$ 2,500	$ 4,200	$ 1,600

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2025
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - Assumptions Used in Black-Scholes Option Pricing Model (Details) - $ / shares	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	3.67%	3.60%	3.54%
Risk-free interest rate, maximum	4.38%	4.66%	4.81%
Expected volatility, minimum	111.61%	109.98%	100.97%
Expected volatility, maximum	123.58%	119.81%	111.71%
Expected dividend yield	0.00%	0.00%	0.00%
Fair value at grant date (in dollars per share)	$ 2.14	$ 1.36	$ 0.69
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	5 years 6 months 3 days	5 years 6 months 3 days	5 years 6 months 3 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years 3 months	6 years 3 months	6 years 3 months

FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 172,689
Warrant liability	2,980	$ 5,176
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	172,689
Warrant liability	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	0
Warrant liability	2,980	5,176
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	0
Warrant liability	$ 0	$ 0

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

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+ Details

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Stock Options
Outstanding beginning balance (in shares)	16,684,325
Granted (in shares)	5,464,077
Exercised (in shares)	(1,205,853)
Expired (in shares)	(1,165,336)
Canceled and forfeited (in shares)	(1,624,955)
Outstanding ending balance (in shares)	18,152,258	16,684,325
Options exercisable at end of period (in shares)	9,819,097
Vested and expected to vest at end of period (in shares)	18,152,258
Weighted-Average Exercise Price
Outstanding beginning balance (in dollars per share)	$ 3.19
Granted (in dollars per share)	2.48
Exercised (in dollars per share)	1.40
Expired (in dollars per share)	8.67
Canceled and forfeited (in dollars per share)	1.99
Outstanding ending balance (in dollars per share)	2.85	$ 3.19
Options exercisable at end of period, weighted-average exercise price (in dollars per share)	3.56
Vested and expected to vest at end of period, weighted-average exercise price ( in dollars per share)	$ 2.85
Weighted-Average Contractual Life (years)
Options outstanding, weighted-average remaining contractual life (in years)	6 years 11 months 19 days	7 years 2 months 1 day
Options exercisable at end of period, weighted-average remaining contractual life (in years)	5 years 7 months 2 days
Vested and expected to vest at end of period, weighted-average contractual life (in years)	6 years 11 months 19 days
Options outstanding, aggregate intrinsic value	$ 3,690	$ 6,797
Exercisable, aggregate intrinsic value	2,624
Vested and expected to vest at end of period, aggregate intrinsic value	$ 3,690

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2025

Accounting Policies [Abstract]

Basis of Presentation

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the U.S., or GAAP. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or FASB.

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All significant intercompany balances and transactions have been eliminated in the consolidated financial statements herein.

Use of Estimates

The preparation of financial statements in conformity with GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, revenue and expenses, classification of the expenses, assets and liabilities and the disclosure of contingent assets and liabilities as of and during the reported period. On an ongoing basis, management evaluates its estimates. Management bases its estimates and assumptions on historical experience when available and on various factors, including expected business and operational changes, sensitivity and volatility associated with the assumption that it believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of the assets and liabilities that are not readily apparent from other sources. In certain circumstances, management must apply significant judgment in this process. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management selects an amount that falls within that range of reasonable estimates. Although, the Company regularly assesses these estimates, actual results could differ materially from these estimates. Changes in estimates are recorded in the period they become known.

Significant estimates and judgments reflected in these consolidated financial statements include, but are not limited to: accrued expenses, other long-term liabilities, a liability related to settlement royalties, revenues, including various rebates, returns and provisions related to product sales, inventories, classification of expenses between cost of goods sold, R&D and selling, general and administrative, long-term assets, including the Company's right-of-use assets and goodwill.

Cash, Cash Equivalents and Restricted Cash

In determining its cash, cash equivalents and restricted cash, the Company considers only those highly liquid investments, readily convertible to cash within 90 days from the date of purchase to be cash equivalents. As of December 31, 2025, cash and cash equivalents primarily included cash on hand and money market funds.

Restricted cash represents amounts required to secure the outstanding letter of credit in connection with the Company’s office and laboratory space in Cambridge, Massachusetts, or the Cambridge Lease. Restricted cash is included in "prepaid expenses and other current assets" in the consolidated balance sheet as of December 31, 2025 and in “other long-term assets” in the consolidated balance sheet as of December 31, 2024.

Fair Value of Financial Instruments

Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required to be recorded at fair value, management considers the principal or most advantageous market in which it would transact and considers assumptions that market participants would use when pricing the asset or liability. ASC Topic 820, Fair Value Measurement, establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. To the extent the valuation is based on models or inputs that are less observable in the market, the determination of fair values requires more judgment. A financial instrument categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The three levels of inputs that may be used to measure fair value are:

•Level 1 – unadjusted quoted prices in active markets for identical assets or liabilities to the reporting entity at the measurement date.

•Level 2 – quoted prices for similar assets or liabilities in markets that are not active, or for which all significant inputs are observable, either directly or indirectly, for substantially the full term of the asset or liability.

•Level 3 – unobservable inputs for the asset or liability used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at the measurement date.

Accounts Receivable

The Company’s accounts receivable represent amounts due to the Company from product sales and from its collaboration, license and other agreements. Royalties that have not been invoiced as of the balance sheet date are recorded as unbilled accounts receivable. Accounts receivable arising from product sales primarily represent amounts due from the Company's customers, net of allowances for customer discounts and chargebacks. The Company deducts trade allowances for prompt payment, among other certain discounts or chargebacks, from its accounts receivable based on its experience that the Company’s customers will earn these discounts and fees.

Concentrations of Risk and Off-Balance Sheet Risk

Credit Risk

Cash, cash equivalents and accounts receivable are the only financial instruments that potentially subject the Company to concentrations of credit risk. The Company maintains cash accounts principally at two financial institutions in the U.S., which at times, may exceed the Federal Deposit Insurance Corporation's limits. The Company has not experienced any losses from cash balances in excess of the insurance limit. The Company's management does not believe the Company is exposed to significant credit risk at this time due to the financial condition of the financial institutions where its cash is held.

The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when collection becomes doubtful. Provisions are made based upon a specific review of all significant outstanding receivables and the overall quality and age of those invoices not specifically reviewed as well as historical payment patterns and existing economic factors. The Company believes that credit risks associated with its customers and collaboration partners are not significant.

Off-Balance Sheet Accounts

The Company has no significant off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangement. See Note 9, Leases, for further details.

Manufacturing and Distribution Risk

The Company is dependent on third-party manufacturers, logistics companies and distributors to supply products for commercial activities associated with its products and product candidates, as applicable. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients, or APIs, and formulated drugs related to the Company's product and product candidate activities. These activities, including the commercialization of Auryxia and Vafseo, could be adversely affected by a significant interruption in the supply of APIs and formulated drugs or distribution of finished product to the market.

Inventories, including Pre-Launch Inventories

The Company values its inventories at the lower-of-actual cost or net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials, manufacturing services and overhead, on a first-in, first-out basis. Inventory expected to be utilized beyond one year is recorded in inventories, long-term on the consolidated balance sheets.

Prior to obtaining regulatory approval for an investigational product candidate, the Company expenses costs relating to production of pre-launch inventory as R&D expense in its consolidated statements of operations and comprehensive loss in the period incurred. After regulatory approval has been received, the Company capitalizes such inventory costs. Products used in clinical trials are expensed as R&D expense in the statement of operations and comprehensive loss.

The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and writes down any excess or obsolete inventory to its net realizable value in the period in which the impairment is identified through cost of product and other revenue in the consolidated statements of operations and comprehensive loss.

Additionally, the Company’s product is subject to strict quality control and monitoring that is performed throughout the manufacturing process, including release of work-in-process to finished goods. In the event that certain batches or units of product do not meet quality specifications, the Company will record a write-down of any potential unmarketable inventory to its estimated net realizable value and record the expense as cost of product and other revenue in the consolidated statements of operations and comprehensive loss.

The Company prepays for certain manufacturing costs, including raw materials and drug substance, to its CMOs which are included in prepaid expenses and other current assets on the consolidated balance sheets.

Property and Equipment

Property and equipment are recorded at cost, less accumulated depreciation. Expenditures for repairs and maintenance are expensed as incurred. Depreciation expense is recognized using the straight-line method over the estimated useful lives, which are typically:

Asset Category

Estimated Useful Life

Computer equipment and software

3 years

Furniture and fixtures

5 years

7 years

Laboratory and other equipment

7 years

Leasehold improvements

Shorter of the useful life or remaining lease term

Maintenance and repairs to an asset that do not improve or extend its life are charged to operations. When assets are retired or otherwise disposed of, the assets and related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the Company's consolidated statements of operations and comprehensive loss.

Intangible Asset

The Company maintained a definite-lived intangible asset related to developed product rights for Auryxia. The intangible asset was initially recorded at fair value and was stated net of accumulated amortization. The Company amortized its intangible asset that had a finite life using the straight-line method over the estimated useful life of six years.

Goodwill

Goodwill reflects the excess purchase price over the fair value of the net tangible and intangible assets acquired in a business combination.

Goodwill is evaluated for impairment on an annual basis, and more frequently if indicators are present or changes in circumstances suggest that impairment may exist. The Company compares the fair value of its reporting unit to its carrying value. If the carrying value of the net assets assigned to the reporting unit exceeds the fair value of its reporting unit, the Company would record an impairment loss equal to the difference. The Company operates in one operating segment which the Company considers to be the only reporting unit.

Impairment of Long-Lived Assets and Intangible Asset Subject to Amortization

Long-lived assets primarily include property and equipment, right of use assets and an intangible asset. The Company evaluates its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of such asset groups may not be recoverable. The recoverability of asset groups to be held and used is measured by a comparison of the carrying amount of an asset group to the future undiscounted net cash flows expected to be generated by the asset group. If such asset groups are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the fair value of the asset group.

Leases

The Company made an accounting policy election not to recognize leases with an initial term of twelve months or less within its consolidated balance sheets and to recognize those lease payments as an expense on a straight-line basis in its consolidated statements of operations and comprehensive loss. The Company also made the accounting policy election not to separate the non-lease components from the lease components for its building leases and, rather, account for each non-lease component and lease component as a single component.

The Company determines if an arrangement is a lease at inception. An arrangement is determined to contain a lease if the contract conveys the right to control the use of an identified property, plant or equipment for a period of time in exchange for consideration. If the Company can benefit from the various underlying assets of a lease on their own or together with other resources that are readily available, or if the various underlying assets are neither highly dependent on nor highly interrelated with other underlying assets in the arrangement, they are considered to be a separate lease component. In the event multiple underlying assets are identified, the lease consideration is allocated to the various components based on each of the component’s relative fair value.

Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent its obligation to make lease payments arising from the leasing arrangement. The right-of-use asset and operating lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The Company uses the implicit rate when readily determinable and uses an estimate of its incremental borrowing rate when the implicit rate is not readily determinable based upon the available information at the commencement date of lease inception. The incremental borrowing rate is determined using a credit rating scoring model to estimate the Company’s credit rating, adjusted for collateralization. The calculation of the right-of-use asset includes any lease payments made and excludes any lease incentives. If a lease includes an option to extend or terminate the lease, the Company reflects the option in the lease term if it is reasonably certain the Company will exercise the option.

The Company’s operating leases are reflected in operating right-of-use assets, accrued expenses and other current liabilities and long-term operating lease liabilities in its consolidated balance sheets.

The Company accounts for the liability related to sale of future royalties as a debt financing, amortized under the effective interest rate method over the estimated life of the related expected royalty stream. The liability related to sale of future royalties and the debt amortization are based on the Company’s current estimates of future royalties expected to be paid over the life of the arrangement. The Company will periodically assess the expected royalty payments. To the extent the Company’s estimates of future royalty payments are greater or less than previous estimates or the estimated timing of such payments is materially different than previous estimates, the Company will adjust the effective interest rate and recognize related non-cash interest expense on a prospective basis. In the event the Company's estimates of future royalties are less than the proceeds from the sale of future royalties, the Company will not recognize related non-cash interest expense. Non-cash royalty revenue is reflected as royalty revenue within license, collaboration and other revenue, and non-cash amortization of debt is reflected as interest expense in the consolidated statements of operations and comprehensive loss.

Working Capital Fund Liability

Working Capital Fund Liability (Previously Referred to as Refund Liability to Customer)

The Company accounts for the Working Capital Fund liability as a debt arrangement, which is recorded at net present value. When the funds were received, the Company recorded an initial discount on the Working Capital Fund liability and a corresponding deferred gain to the Working Capital Fund liability. The discount on the Working Capital Fund liability is being amortized to interest expense on the consolidated statement of operations and comprehensive loss and the deferred gain is being amortized to other income on the consolidated statement of operations and comprehensive loss over the expected term of the arrangement. On a quarterly basis, the Company reassesses the effective rate and will adjust the rate prospectively, if needed.

The Company accounts for the liability related to settlement royalties as a liability, amortized using the effective interest method over the term of the arrangement. The liability related to settlement royalties and the amortization are based on the Company’s current estimates of future royalties expected to be paid over the life of the arrangement. To the extent the Company’s estimates of future royalty payments are greater or less than previous estimates or the estimated timing of such payments is materially different than previous estimates, the Company will adjust the effective interest rate and recognize related non-cash interest expense on a prospective basis.

Warrant Liability

The Company accounts for the warrant liability under ASC 815, Derivatives and Hedging, as it could potentially require net cash settlement outside of the Company’s control. The warrant liability is measured at fair value each reporting period and when a warrant is exercised, with changes in fair value presented within the consolidated statements of operations and comprehensive loss.

Excess Firm Purchase Commitment Liability

At each reporting period, the Company assesses whether there are excess firm non-cancelable purchase commitment liabilities, resulting from supply agreements with third-party CMOs. The determination of excess firm purchase commitment liabilities requires judgment, including consideration of many factors, such as estimates of future product demand, current and future market conditions, impact of the Company's loss of exclusivity, expiration and utilization of drug substance under firm purchase commitments, and contractual minimums. Any changes in the firm purchase commitment liability are recorded in cost of product and other revenue in the consolidated statements of operations and comprehensive loss.

Revenue Recognition

The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers, or ASC 606, which applies to all contracts with customers, except for contracts that are within the scope of other standards. Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, it performs the following five steps:

(i)identify the contract(s) with a customer;

(ii)identify the performance obligations in the contract;

(iii)determine the transaction price;

(iv)allocate the transaction price to the performance obligations in the contract; and

(v)recognize revenue when (or as) the entity satisfies a performance obligation.

The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied.

The Company does not include a financing component to its estimated transaction price at contract inception unless it estimates that certain performance obligations will not be satisfied within one year. Additionally, the Company recognizes the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is one year or less.

Product Revenue, Net

The Company recognizes product revenues on sales of Auryxia and Vafseo primarily attributable to a limited number of customers, including dialysis organizations, wholesale distributors, certain specialty pharmacy providers and its authorized generic distribution partner, in the U.S., which accounts for the largest portion of the Company's total revenue. These customers resell the Company’s product to health care providers and patients. In addition to distribution agreements with customers, the Company enters into arrangements with health care providers and payors that provide for government-mandated and/or privately-negotiated rebates, chargebacks and discounts with respect to the purchase of the Company’s products. The Company’s payment terms are consistent with prevailing practice in the respective markets in which the Company does business. Most of the Company’s customers make payments based on contract terms, which are not affected by contingent events that could impact the transaction price. Payment terms fall within the one-year guidance for the practical expedient, which allows the Company to forgo adjustment of the contractual payment amount of consideration for the effects of a significant financing component.

The Company recognizes revenue on product sales when the customer obtains control of the Company’s products, which occurs at a point in time, typically upon receipt of the product by the Company's customer. The Company expenses incremental costs of obtaining a contract, such as sales commissions, as and when incurred, if the expected amortization period of the asset that it would have recognized is one year or less. Sales commissions are recorded in selling, general and administrative expense in the statements of operations and comprehensive loss.

Revenue from product sales is recorded at the net sales price, or Transaction Price, which includes estimates of variable consideration for which provisions are established and which result from discounts, returns, chargebacks, rebates, co-pay assistance and other allowances offered within contracts between the Company and its customers, health care providers, payors and other indirect customers relating to the Company’s sales of its products. When appropriate, these estimates take into consideration a range of possible outcomes which are probability-weighted in accordance with the expected value method in ASC 606 for relevant factors such as the Company’s historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns.

The amount of variable consideration that is included in the Transaction Price may be constrained, and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. The provisions are classified as reductions to accounts receivable, net of payable, if the trade discount and/or allowance will be credited to the customer or accrued expenses and other current liabilities or other long-term liabilities, if payable to a third-party in the consolidated balance sheets.

Commercial Rebates—The Company contracts with dialysis organizations, wholesale distributors and certain specialty pharmacy providers for the payment of rebates with respect to utilization of Auryxia and Vafseo. The Company estimates commercial rebates based upon customers' actual purchase level during the quarterly or annual rebate purchase period, and the corresponding contractual rebate tier each customer is expected to achieve. The Company estimates these rebates and records such estimates in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of an accrued liability.

Trade Discounts and Allowances—The Company generally provides customers with prompt pay discounts and pays fees for sales order management, data and distribution services, which are explicitly stated in its contracts. Trade discounts and allowances are recorded as a reduction of revenue within the consolidated statements of operations and comprehensive loss in the period the related product revenue is recognized. The Company estimates that, based on its

experience, its customers will earn these discounts and fees, and the Company will deduct the full amount of these discounts and fees from its gross product revenues and accounts receivable at the time such revenues are recognized.

Product Returns—Consistent with industry practice, subject to certain caps for certain customers, the Company generally offers customers a limited right of return which allows for the product to be returned when the product expiry is within an allowable window, when the quantity delivered is different than quantity ordered, the product is damaged in transit prior to receipt by the customer or is subject to a recall. This right of return generally lapses once the product is provided to a patient or generally, if the bottle has been opened. The Company estimates the amount of its product sales that may be returned and records this estimate as a reduction of revenue in the period the related product revenue is recognized. The Company currently estimates product return provision using its own historical return information as well as recent trends on lots still subject to the return window. In addition, certain customers are subject to an annual cap on returns of 2% of gross sales in any given year.

Provider Chargebacks and Discounts—Chargebacks for fees and discounts to providers represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to customers who directly purchase the product from the Company. Customers charge the Company for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. These provisions are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the customer’s resale of the product. Provisions for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel at each reporting period end that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed but for which the Company has not yet issued a credit.

Government Rebates—The Company is subject to discount obligations under state Medicaid programs and other government programs. The Company estimates its Medicaid and other government programs rebates based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These provisions are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included in accrued expenses and other current liabilities in the consolidated balance sheets. For Medicare, the Company also estimates the number of patients in the prescription drug coverage gap for whom the Company will owe an additional liability under the Medicare Part D program. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period.

Other Incentives—The Company offers a voluntary patient co-pay assistance program, which provides financial assistance to qualified commercially insured patients with prescription drug co-payments required by payors. The calculation of the accrual for co-pay assistance is based on actual claims processed during a given period plus an estimate of the amount the Company expects to pay based on historical utilization rates for the product that has been recognized as revenue but is estimated to be remaining in in the distribution channel at the end of each reporting period.

License, Collaboration and Other Revenues

The Company enters into license and collaboration agreements within the scope of ASC 606, under which it licenses certain rights to its product candidates to third parties. The terms of these arrangements typically include the following: (i) non-refundable, up front licenses fees associated with the licensing of intellectual property; (ii) development, regulatory and commercial milestone payments; (iii) drug product the Company supplies in connection with certain license and collaboration agreements and (iv) royalties earned on net sales of licensed products.

In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company implements the five-step model noted above. As part of the accounting for these arrangements, the Company develops assumptions that require judgment to determine whether the individual promises should be accounted for as separate performance obligations or as a combined performance obligation, and to determine the stand-alone selling price for each performance obligation identified in the contract. A deliverable represents a separate performance obligation if both of the following criteria are met: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer, and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.

Licenses of Intellectual Property

If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Milestone Payments

At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to assess the milestone as probable of being achieved. There is considerable judgment involved in determining whether a milestone is probable of being reached at each specific reporting period. Milestone payments that are not within the control of the Company or the customer, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenues as, or when, the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration, license and other revenue in the period of adjustment.

Drug Product Supply

Collaboration and license arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the licensee’s discretion are generally considered as options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as a separate performance obligation. If the Company is entitled to additional payments when the licensee exercises these options, any payments are recorded in license, collaboration and other revenues when the licensee obtains control of the goods, which is generally upon delivery.

Royalties

The Company will recognize sales-based royalties, including milestone payments based on the level of net sales, at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied).

Collaborative Arrangements

The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC Topic 808, Collaborative Arrangements, or ASC 808. Accordingly, the elements of the collaboration agreements that represent activities in which both parties are active participants and to which both parties are exposed to the significant risks and rewards that are dependent on the commercial success of the activities are recorded as collaborative arrangements. The Company considers the guidance in ASC 606-10-15, Revenue from Contracts with Customers – Scope and Scope Exceptions, in determining the appropriate treatment for the transactions between the Company and its collaborative partners and the transactions between the Company and third parties. Generally, the classification of transactions under the collaborative arrangements is determined based on the nature and contractual terms of the arrangement along with the nature of the operations of the participants. To the extent product revenue is generated from the collaboration, the Company recognizes its share of the net sales on a gross basis if the Company is deemed to be the principal in the transactions with customers, or on a net basis if the Company is instead deemed to be the agent in the transactions with customers, consistent with the guidance in ASC 606.

Cost of Goods Sold

Cost of Product and Other Revenue

Cost of product and other revenue includes costs closely correlated or directly related to the costs to manufacture commercial products, including costs paid to the Company's contract manufacturing organizations, or CMOs, as well as indirect costs. Direct and indirect costs include fees for packaging, shipping, insurance and quality assurance, idle capacity charges, routine testing costs, routine ongoing efforts to improve existing commercial products, reserves for excess inventory, write-offs for inventory that fails to meet specifications or is otherwise no longer suitable for commercial sale, including scrap,

changes in firm purchase commitment liability and royalties due to the licensor of Auryxia related to U.S. and Japan product sales recognized during the period. In addition, cost of product and other revenue includes the amortization of development product rights for the Auryxia intangible asset. The Company also includes personnel-related costs, including salaries and bonuses, employee benefits and stock-based compensation attributable to employees in particular functions and associated directly with the manufacturing of our commercial products.

Further, the Company includes in cost of product and other revenue costs to manufacture drug product provided to customers for which it has a license agreement or authorized generic distribution and supply agreement. Cost of goods sold for a newly launched product may not include the full cost of manufacturing until the initial pre-launch inventory is depleted, and additional inventory is manufactured and sold.

Until the Company received regulatory approval for Vafseo in the U.S. in March 2024, the Company recorded expenses incurred for the manufacture of pre-launch inventory that would support a U.S. launch as R&D expense. The costs associated with the pre-launch inventory for the Medice Territory were expensed to R&D through April 2023 when marketing authorization was received.

Research and Development Expenses

R&D costs are expensed as incurred. Internal R&D expenses are comprised of costs incurred in providing R&D activities, including salaries and bonuses, employee benefits, stock-based compensation for personnel engaged in R&D activities. In addition, they include facility costs, including the laboratory and an allocation of office space for utilization by R&D staff, depreciation expense on the laboratory equipment as well as other direct costs such as lab supplies and equipment.

External R&D costs include development of potential new manufacturing processes and methods for both commercial and non-commercial products, conceptual formulation and design of possible product and process alternatives, research compounds and clinical manufacturing costs, costs incurred for consultants and other outside services, such as data management and statistical analysis support and materials and supplies used in support of the clinical and preclinical programs and costs paid to clinical resource organizations, or CRO, including investigative sites that conduct the Company's clinical trials.

Non-refundable advance payments for goods and services are recorded in prepaid and other current assets in the consolidated balance sheets and expensed when the activity is performed or when the goods are received. In addition, the costs associated with pre-launch inventory, including the cost of raw materials, costs paid to contract manufacturers for inventory manufacturing, freight and custom charges for Vafseo were expensed as R&D prior to regulatory approval.

Selling, General, and Administrative Expenses/Patent Costs

Selling, General and Administrative Expenses

Selling, general and administrative, or SG&A, expenses consist primarily of compensation for personnel, including stock-based compensation related to commercial, marketing, executive, finance and accounting, information technology, corporate and business development and human resource functions. Other SG&A expenses include costs for marketing initiatives for the Company's commercial products, market research and analysis on the Company's commercial products and potential product candidates, conferences and trade shows, travel expenses, professional services fees (including legal, patent, accounting, audit, tax, and consulting fees), insurance costs, general corporate expenses and allocated facilities-related expenses, including rent and maintenance of facilities. Costs associated with advertising are expensed in the period incurred and are included in selling, general and administrative expenses. For the years ended December 31, 2025, 2024 and 2023, advertising expenses totaled $7.6 million, $4.6 million and $1.0 million, respectively.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Such amounts incurred are classified as SG&A expenses in the accompanying consolidated statements of operations and comprehensive loss.

Stock-Based Compensation

The Company’s stock-based compensation program allows for grants of common stock options, restricted stock awards, performance-based restricted stock units, or PSUs, stock appreciation rights, or SARs and restricted stock units. Grants are awarded to employees and non-employees, including directors.

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation, or ASC 718. ASC 718 requires all stock-based payments to employees and non-employees, including modifications to existing stock awards, to be recognized in the statements of operations and comprehensive loss based on their fair values. The Company estimates the fair value of options granted using the Black-Scholes option pricing model, or Black-Scholes. The Company uses the market price at the time of grant to determine the fair value of restricted stock awards and performance-based restricted stock awards.

The Black-Scholes option pricing model requires the input of certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Prior to 2017, due to the lack of company-specific historical and implied volatility data for trading the Company’s stock in the public market, the Company had based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility was calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the Securities and Exchange Commission, or SEC, Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post-vesting termination behavior among its employee population. For options granted to non-employees, the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk-free interest rate is based on U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The Company recognizes forfeitures as they occur.

The Company’s stock-based awards are subject to either service or performance-based vesting conditions. Compensation expense related to awards to employees and non-employees with service-based vesting conditions is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term, and is adjusted for pre-vesting forfeitures in the period in which the forfeitures occur. Compensation expense related to awards to employees and non-employees with performance-based vesting conditions is recognized based on the grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable.

For awards with performance conditions in which the award does not vest unless the performance condition is met, the Company recognizes expense if, and to the extent that, the Company estimates that achievement of the performance condition is probable. If the Company concludes that vesting is probable, it recognizes expense from the date it reaches this conclusion through the estimated vesting date.

For market-based awards, the Company recognizes expense on a straight-line basis over the requisite service period, regardless of whether the market condition has been satisfied. Market-based performance stock unit awards vest upon the achievement of the performance target. Forfeitures are accounted for as incurred. The Company estimates the fair value of these awards as of the grant date using a Monte Carlo simulation that incorporates option-pricing inputs. This simulation covers the period from the grant date through the end of the derived requisite service period. Volatility as of the grant date is estimated based on historical daily volatility of the Company's common stock over a period of time, which is equivalent to the expected term of the award. The risk-free interest rate is based on the U.S. Treasury Note rate, as of the week the award is issued, with a duration that most closely resembles the expected term of the award.

Income Taxes

Income taxes are recorded in accordance with FASB Topic 740, Income Taxes, or ASC 740, which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. All deferred taxes as of December 31, 2025, 2024 and 2023 are classified as non-current within the income tax provision. See Note 15, Income Taxes, for further information.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2025, 2024 and 2023, the Company does not have any significant uncertain tax positions. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense.

Business Combinations and Asset Acquisitions

The Company evaluates acquisitions of assets and other similar transactions to assess whether or not the transaction should be accounted for as a business combination or asset acquisition by first applying a screen test to determine if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. If the screen test is met, the transaction is accounted for as an asset acquisition. If the screen test is not met, further determination is required as to whether or not the Company has acquired inputs and processes that have the ability to create

outputs which would meet the requirements of a business. If determined to be an asset acquisition, the Company accounts for the transaction under ASC 805-50, which requires the acquiring entity in an asset acquisition to recognize assets acquired and liabilities assumed based on the cost to the acquiring entity on a relative fair value basis, which includes transaction costs in addition to consideration given. Goodwill is not recognized in an asset acquisition and any excess consideration transferred over the fair value of the net assets acquired is allocated to the identifiable assets based on relative fair values. In-process research and development, or IPR&D, projects with no alternative future use are recorded in R&D expense upon acquisition, and contingent consideration obligations incurred in connection with an asset acquisition are recorded when it is probable that they will occur and they can be reasonably estimated.

Net Loss per Share

Basic net loss per share is calculated by dividing net loss by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting weighted-average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of the diluted net loss per share calculation, common stock options, stock appreciation rights, warrants and RSUs as well as restricted stock, if the Company was to issue any, are considered to be common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Diluted net income per share is calculated by dividing the net income by the weighted-average common shares outstanding for the period, including any dilutive effect from outstanding options, warrants, restricted stock and RSUs using the treasury stock method.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or CODM, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company operates its business in a single segment and as one reporting unit, which is how its chief operating decision maker (who is the Company's president and chief executive officer) reviews financial performance and allocates resources. The Company views its operations as and manages its business in one operating segment.

New Accounting Pronouncements - Recently Adopted and Not Yet Adopted

New Accounting Pronouncements - Recently Adopted

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. ASU 2023-09 requires public companies to annually (i) disclose specific categories in the rate reconciliation and (ii) provide additional information for reconciling items that meet a quantitative threshold (if the effect of those reconciling items is equal to or greater than 5 percent of the amount computed by multiplying pretax income or loss by the applicable statutory income tax rate). ASU 2023-09 is effective for the annual reporting periods in fiscal years beginning after December 15, 2024. See Note 15, Income Taxes, for further information.

New Accounting Pronouncements - Not Yet Adopted

In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses, which requires new tabular disclosures in the notes to consolidated financial statements, disaggregating certain cost and expense categories within relevant captions on the consolidated statements of operations and comprehensive loss. The prescribed cost and expense categories requiring disaggregated disclosures include purchases of inventory, employee compensation, depreciation and intangible asset amortization, along with certain other expense disclosures already required by U.S. GAAP that would need to be integrated within the new tabular disaggregated expense disclosures. Additionally, the amendments also require the disclosure of total selling expenses and an entity's definition of those expenses. ASU 2024-03 will be effective for annual reporting periods in fiscal years beginning after December 15, 2026, and interim reporting periods in fiscal years beginning after December 31, 2027. Early adoption is permitted and the amendments should be applied on a prospective basis. Retrospective application is permitted. The Company is currently reviewing the impact that the adoption of ASU 2024-03 may have on its expense disclosures in the notes to the consolidated financial statements.

In July 2025, the FASB issued ASU 2025-05, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses for Accounts Receivable and Contract Assets. ASU 2025-05 provides a practical expedient that all entities can use when estimating expected credit losses for current accounts receivable and current contract assets arising from transactions accounted for under ASC 606, Revenue from Contracts with Customers. Under this practical expedient, an entity is allowed to assume that the current conditions it has applied in determining credit loss allowances for current accounts receivable and current contract assets remain unchanged for the remaining life of those assets. ASU 2025-05 is effective for fiscal years beginning after December 15, 2025, and interim reporting periods in those years. Entities that elect the practical expedient and, if applicable, make the accounting policy election are required to apply the amendments prospectively. The Company is

currently evaluating ASU 2025-05 and does not expect it to have a material effect on the Company’s consolidated financial statements.

In September 2025, the FASB issued ASU 2025-06, Intangibles - Goodwill and Other - Internal-Use Software, which removes all references to prescriptive and sequential software development stages (referred to as "project stages"). An entity will be required to start capitalizing software costs when (i) management has authorized and committed to funding the software project and (ii) it is probable that the project will be completed and the software will be used to perform the function intended (referred to as the "probable-to-complete recognition threshold"). ASU 2025-06 is effective for fiscal years beginning after December 15, 2027, and interim reporting periods within those annual periods. Early adoption is permitted as of the beginning of the annual reporting period. The Company is currently evaluating ASU 2025-06 and does not expect it to have a material effect on the Company’s consolidated financial statements.

LEASES - Schedule of Future Commitments under Non-Cancelable Leases (Details) $ in Thousands	Dec. 31, 2025 USD ($)
Leases [Abstract]
2026	$ 3,613
Less: present value adjustment	(65)
Current operating lease liabilities	$ 3,548

INCOME TAXES - Schedule of Effective Reconciliation Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Amount
U.S. federal statutory tax rate	$ (781)
State and local income taxes, net of federal income tax effect	1,283
Research and development tax credits	(988)
Changes in valuation allowances	(533)
Meals & entertainment	165
Lobbying contributions	294
Stock compensation	680
162(m) compensation limit	731
Pharma fee	105
Warrant liability	651
Other	18
Total income taxes	$ 1,624	$ 0	$ 0
Percent
U.S. federal tax at statutory rate	21.00%	21.00%	21.00%
State and local income taxes, net of federal income tax effect	(34.50%)	0.60%	2.70%
Research and development tax credits	26.60%
Changes in valuation allowances	14.30%	(32.50%)	(9.10%)
Meals & entertainment	(4.40%)
Lobbying contributions	(7.90%)
Stock compensation	(18.30%)
162(m) compensation limit	(19.60%)
Pharma fee	(2.80%)
Warrant liability	(17.50%)
Other	(0.60%)	0.00%	0.50%
Effective tax rate	(43.70%)	0.00%	0.00%

INCOME TAXES - Schedule of Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income (loss) from continuing operations before income taxes:
United States	$ (3,721)	$ (69,410)	$ (51,925)
Foreign	0	0	0
Loss before income taxes	$ (3,721)	$ (69,410)	$ (51,925)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

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+ Details

INCOME TAXES - Schedule of Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Deferred tax assets:
Accrued expenses and other current liabilities	$ 9,374	$ 1,757
Deferred revenue	15,765	13,222
Sale of royalty	12,251	13,595
R&D credits	7,726	6,152
Capitalized R&D costs	11,873	21,270
Net operating loss carryforward	289,712	291,723
ASC 842 lease liability	832	2,248
Working Capital Fund liability	9,366	10,123
Intangible assets	4,631	2,040
Other	22,021	29,048
Total deferred tax assets	383,551	391,178
Less valuation allowance	(382,001)	(387,803)
Total deferred tax assets, net of valuation allowance	1,550	3,375
Deferred tax liabilities:
481(a) adjustments	(670)	(1,271)
ROU asset (ASC 842)	(859)	(2,065)
Other	(21)	(39)
Total deferred tax liabilities	(1,550)	(3,375)
Net deferred tax liability	$ 0	$ 0

ADDITIONAL BALANCE SHEET DETAIL (Tables)

12 Months Ended

Dec. 31, 2025

Payables and Accruals [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets are as follows (in thousands):


	December 31,
Description	2025	2024
Prepaid manufacturing	—	4,029
Restricted cash	1,699	—
Other	3,771	7,321
Total prepaid expenses and other current assets	5,470	11,350

Schedule of Other Long-Term Assets

Other long-term assets are as follows (in thousands):


	December 31,
Description	2025		2024
Long-term inventories	$	59,129	$	34,953
Restricted cash	—		1,680
Other	552		744
Total other long-term assets	$	59,681	$	37,377

Schedule of Components of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities are as follows (in thousands):


	December 31,
Description	2025		2024
Product revenue allowances	$	7,916	$	9,657
Product rebates	64,674		6,070
Product return provisions, current portion	2,375		5,295
Compensation and related benefits	11,018		9,194
Operating lease liabilities, current portion	3,548		5,400
Royalties due to Panion & BF Biotech, Inc.	3,924		3,543
Liability related to sale of future royalties, current portion	1,664		2,039
Professional fees	1,597		1,452
Accrued manufacturing costs	1,808		1,468
BioVectra, Inc. termination fees, current portion	—		7,204
Settlement royalties liability, current portion	12,516		5,924
Clinical trial costs	1,188		1,885
Restructuring costs, current portion	—		489
Payments due to Q32	5,000		—
Other	4,488		3,840
Total accrued expenses and other current liabilities	$	121,716	$	63,460

Insider Trading Policies and Procedures	12 Months Ended
Insider Trading Policies and Procedures	Dec. 31, 2025
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

INCOME TAXES

12 Months Ended

Dec. 31, 2025

Income Tax Disclosure [Abstract]

INCOME TAXES

Income before provision for income taxes was as follows (in thousands):


	Years Ended December 31,
	2025		2024		2023
United States	$	(3,721)	$	(69,410)	$	(51,925)
Foreign	—		—		—
Income (loss) before taxes	$	(3,721)	$	(69,410)	$	(51,925)


	Years Ended December 31,
	2025		2024		2023
Current:
Federal	$	—	$	—	$	—
State	1,624		—		—
Foreign	—		—		—
Total current	1,624		—		—
Deferred:
Federal	—		—		—
State	—		—		—
Foreign	—		—		—
Total deferred	—		—		—
Total income taxes	$	1,624	$	—	$	—


	Year Ended December 31,
	2025
	(In thousands)		Percent
U.S. federal statutory tax rate	$	(781)	21.0	%
State and local income taxes, net of federal income tax effect(1)	1,283		(34.5)
Tax credits
Research and development tax credits	(988)		26.6
Changes in valuation allowances	(533)		14.3
Nontaxable or nondeductible items
Meals & entertainment	165		(4.4)
Lobbying contributions	294		(7.9)
Stock compensation	680		(18.3)
162(m) compensation limit	731		(19.6)
Pharma fee	105		(2.8)
Warrant liability	651		(17.5)
Other Adjustments
Other	18		(0.6)
Effective tax rate	$	1,624	(43.7)	%

(1) The states and local jurisdictions that contribute to the majority (greater than 50%) of the tax effect in this category include Tennessee.

A reconciliation of the provision for income taxes to the amount computed by applying the 21% statutory U.S. federal income tax rate to income before income taxes for years prior to the adoption of ASU 2023-09 is as follows:


	Years Ended December 31,
	2024		2023
U.S. federal tax at statutory rate	21.0	%	21.0	%
State and local tax at statutory rate	0.6		2.7
Research and development tax credits	1.9		0.3
Change in valuation allowance	(32.5)		(9.1)
Other permanent differences	(1.7)		(2.0)
Stock option cancellations	(1.8)		(3.7)
Stock option shortfalls	—		(1.7)
Effect of rate changes	13.5		(7.7)
Provision to return adjustment	(1.0)		(0.3)

Other	—		0.5
Effective tax rate	—	%	—	%

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. When realization of the deferred tax asset is more likely than not to occur, the benefit related to the deductible temporary differences attributable to operations is recognized as a reduction of income tax expense. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. The Company cannot be certain that future taxable income will be sufficient to realize its deferred tax assets. Accordingly, the Company has recorded a valuation allowance against the Company’s otherwise recognizable net deferred tax assets. The Company continues to maintain the underlying tax benefits to offset future taxable income and to monitor the need for a valuation allowance based on the profitability of its future operations. The valuation allowance decreased by approximately $5.8 million for the year ended December 31, 2025 and increased by $22.5 million and $4.7 million during the years ended December 31, 2024 and 2023, respectively. Significant components of the Company’s deferred tax assets and liabilities are as follows (in thousands):


	December 31,
	2025		2024
Deferred tax assets:
Accrued expenses and other current liabilities	$	9,374	$	1,757
Deferred revenue	15,765		13,222
Sale of royalty	12,251		13,595
R&D credits	7,726		6,152
Capitalized R&D costs	11,873		21,270
Net operating loss carryforward	289,712		291,723
ASC 842 lease liability	832		2,248
Working Capital Fund liability	9,366		10,123
Intangible assets	4,631		2,040
Other	22,021		29,048
Total deferred tax assets	383,551		391,178
Less valuation allowance	(382,001)		(387,803)
Total deferred tax assets, net of valuation allowance	1,550		3,375
Deferred tax liabilities:

481(a) adjustments	(670)		(1,271)
ROU asset (ASC 842)	(859)		(2,065)
Other	(21)		(39)
Total deferred tax liabilities	(1,550)		(3,375)
Net deferred tax liability	$	—	$	—

As of December 31, 2025, 2024 and 2023, the Company had approximately $1,240.8 million, $1,245.8 million and $1,230.4 million, respectively, of federal net operating losses, or NOLs, carry-forwards which expire through 2037. Included in the $1,240.8 million of federal NOLs are losses of $663.8 million that will carry forward indefinitely as a result of the Tax Cuts and Jobs Act. Additionally, at December 31, 2025, 2024 and 2023, the Company had approximately $562.2 million, $584.3 million

and $590.8 million, respectively, of state NOL carry-forwards, which expire through 2045. The Company also has approximately $5.0 million of federal research and development tax credit carryforwards which expire through 2045 and $3.4 million of state R&D tax credit carryforwards which expire through 2040.

Under the provisions of the IRC, the NOLs and tax credit carry-forwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOLs and tax credit carryforwards may become subject to an annual limitation under IRC Sections 382 and 383 if there is more than a 50% change in ownership of the stockholders that own 5% or more of the Company’s outstanding stock over a three-year period. The Company completed an evaluation of its ownership changes and concluded that an ownership change did occur on December 12, 2018 for both Akebia and Keryx in connection with the Merger. As a consequence of this ownership change, the Company’s NOLs and tax credit carryforwards allocable to the tax periods preceding the ownership change became subject to limitation under Section 382 of the IRC. The Company reduced its associated deferred tax assets by $44.9 million as a result of the limitation. The Company completed an evaluation of its ownership changes as of December 31, 2025 and concluded that an ownership change had not occurred since the previous evaluation done through December 12, 2018. The Company may experience ownership changes in the future as a result of subsequent shifts in our stock ownership, some of which may be outside the Company’s control. As a result, the Company’s ability to utilize these attributes to offset taxable income may be subject to limitations.

The Company has not conducted a full study of its research and development credit carryforwards. A study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed, and any adjustment is known, no amounts will be presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credit carryforwards and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the balance sheet or statement of operations at this time, if an adjustment were required.

The Company files income tax returns in the U.S. federal and various state and local jurisdictions. For federal and state income tax purposes, the 2024, 2023 and 2022 tax years remain open for examination under the normal three-year statute of limitations. The statute of limitations for income tax audits in the U.S. will commence upon utilization of NOLs and will expire three years from the filing of the tax return the loss was utilized on.

As of December 31, 2025, the Company’s U.S. federal income tax return for the year ended December 31, 2023 is under examination by the Internal Revenue Service. The examination is in its early stages, and no proposed adjustments have been received. The ultimate resolution of this matter is uncertain and could differ from amounts recorded in the consolidated financial statements.

A reconciliation of the beginning and ending amounts of unrecognized tax benefits for the years ending December 31, 2025, 2024 and 2023 are as follows (in thousands):


Balance at December 31, 2022	$	2,697
Reductions based on tax positions of current years	(2,697)
Balance at December 31, 2023	—
Reductions based on tax positions of current years	—
Balance at December 31, 2024	—
Reductions based on tax positions of current years	—
Balance at December 31, 2025	$	—

The Company paid $0.7 million cash for state and local income taxes during the year ended December 31, 2025. The Company did not pay cash for income taxes during the years ended December 31, 2024 and 2023.

- Definition

The entire disclosure for income tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - Stock-Based Compensation Expense Related to Share-Based Awards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 11,283	$ 7,775	$ 9,317
Cost of goods sold
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	683	399	267
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	2,120	1,498	1,964
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	8,480	5,840	6,456
Restructuring
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 0	$ 38	$ 630

SEGMENT INFORMATION - Segment Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Total revenues	$ 236,196	$ 160,180	$ 194,623
Less:
Amortization of intangible asset	0	36,042	36,042
Research and development	62,359	37,652	63,079
Selling, general and administrative	107,480	106,545	100,233
License	3,396	3,220	3,237
Restructuring	0	58	181
Income (loss) from operations	23,499	(50,472)	(46,256)
Other income (expense):
Interest expense	(24,179)	(18,185)	(6,032)
Other income	58	94	887
Change in fair value of warrant liability	(3,099)	(330)	0
Loss on extinguishment of debt	0	(517)	0
Loss on termination of lease	0	0	(524)
Loss before income taxes	(3,721)	(69,410)	(51,925)
Income tax expense	(1,624)	0	0
Net loss	(5,345)	(69,410)	(51,925)
Reportable Segment
Segment Reporting Information [Line Items]
Total revenues	236,196	160,180	194,623
Less:
Direct cost of product and other revenue	28,136	15,970	26,525
Panion royalty	11,326	9,097	10,048
Excess firm purchase commitment charge	0	2,068	1,533
Amortization of intangible asset	0	36,042	36,042
Research and development	62,359	37,652	63,079
Selling, general and administrative	107,480	106,545	100,233
License	3,396	3,220	3,237
Restructuring	0	58	181
Income (loss) from operations	23,499	(50,472)	(46,256)
Other income (expense):
Interest expense	(24,179)	(18,185)	(6,032)
Other income	58	94	887
Change in fair value of warrant liability	(3,099)	(330)	0
Loss on extinguishment of debt	0	(517)	0
Loss on termination of lease	0	0	(524)
Loss before income taxes	(3,721)	(69,410)	(51,925)
Income tax expense	(1,624)	0	0
Net loss	$ (5,345)	$ (69,410)	$ (51,925)

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - Compensation Expense by Type of Award (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 11,283	$ 7,775	$ 9,317
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	5,356	4,036	5,310
Unvested restricted stock units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	5,214	3,655	3,637
Performance RSUs
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	545	0	297
Employee stock purchase plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 168	$ 84	$ 73

SEGMENT INFORMATION

12 Months Ended

Dec. 31, 2025

Segment Reporting [Abstract]

SEGMENT INFORMATION

The Company operates as one operating segment focused on developing and commercializing innovative therapeutics primarily in the U.S. The accounting policies of the segment are the same as those described in Note 2, Summary of Significant Accounting Policies.

The determination of a single business segment is consistent with the consolidated financial information regularly reviewed by the chief executive officer, who is the Company's CODM, in assessing segment performance and deciding how to allocate resources on a consolidated basis.

The CODM makes decisions on resource allocation, assesses performance of the business, and monitors budget versus actual results using income (loss) from operations. Net income (loss) is also a measure that is considered in monitoring budget versus actual results. The measure of segment assets is reported on the consolidated balance sheets as total consolidated assets.

The following table presents information about reported segment revenues, segment profit and significant segment expenses for the years ended December 31, 2025, 2024 and 2023:


	Years Ended December 31,
	2025		2024		2023
Revenues	$	236,196	$	160,180	$	194,623
Less:
Direct cost of product and other revenue	28,136		15,970		26,525
Panion royalty	11,326		9,097		10,048
Excess firm purchase commitment charge	—		2,068		1,533
Amortization of intangible asset	—		36,042		36,042
Research and development	62,359		37,652		63,079
Selling, general and administrative	107,480		106,545		100,233
License	3,396		3,220		3,237
Restructuring	—		58		181
Income (loss) from operations	23,499		(50,472)		(46,256)

Other income (expense)
Interest expense	(24,179)		(18,185)		(6,032)
Other income	58		94		887
Change in fair value of warrant liability	(3,099)		(330)		—
Loss on extinguishment of debt	—		(517)		—
Loss on termination of lease	—		—		(524)
Net loss before income taxes	(3,721)		(69,410)		(51,925)
Income tax expense	(1,624)		—		—
Net loss	$	(5,345)	$	(69,410)	$	(51,925)

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

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+ Details

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2022		184,135,714
Beginning balance at Dec. 31, 2022	$ 5,230	$ 2	$ 1,562,247	$ 6	$ (1,557,025)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs (in shares)		6,189,974
Issuance of common stock, net of issuance costs	6,708		6,708
Proceeds from sale of stock under employee stock purchase plan (in shares)		200,194
Proceeds from sale of stock under employee stock purchase plan	85		85
Stock-based compensation expense	9,317		9,317
Restricted stock unit vesting (in shares)		4,054,407
Exercise of options (in shares)		2,250
Exercise of options	1		1
Net loss	(51,925)				(51,925)
Ending balance (in shares) at Dec. 31, 2023		194,582,539
Ending balance at Dec. 31, 2023	(30,584)	$ 2	1,578,358	6	(1,608,950)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs (in shares)		27,532,942
Issuance of common stock, net of issuance costs	42,495		42,495
Proceeds from sale of stock under employee stock purchase plan (in shares)		189,732
Proceeds from sale of stock under employee stock purchase plan	153		153
Stock-based compensation expense	7,775		7,775
Restricted stock unit vesting (in shares)		2,099,540
Exercise of options (in shares)		444,239
Exercise of options	386		386
Net loss	$ (69,410)				(69,410)
Ending balance (in shares) at Dec. 31, 2024	224,848,992	224,848,992
Ending balance at Dec. 31, 2024	$ (49,185)	$ 2	1,629,167	6	(1,678,360)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs (in shares)		35,287,364
Issuance of common stock, net of issuance costs	66,449		66,449
Warrants exercised, cashless (in shares)		1,408,588
Warrants exercised, cashless	7,494		7,494
Proceeds from sale of stock under employee stock purchase plan (in shares)		187,422
Proceeds from sale of stock under employee stock purchase plan	230		230
Stock-based compensation expense	$ 11,283		11,283
Restricted stock unit vesting (in shares)		2,486,599
Exercise of options (in shares)	1,205,853	1,205,853
Exercise of options	$ 1,684		1,684
Net loss	$ (5,345)				(5,345)
Ending balance (in shares) at Dec. 31, 2025	265,424,818	265,424,818
Ending balance at Dec. 31, 2025	$ 32,610	$ 2	$ 1,716,307	$ 6	$ (1,683,705)

LICENSE, COLLABORATION AND OTHER REVENUE - Schedule of Revenues Recognized From License, Collaboration and Other Significant Agreements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 236,196	$ 160,180	$ 194,623
License, collaboration and other revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	8,864	8,000	24,322
License, collaboration and other revenue \| Medice
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	411	22	10,968
License, collaboration and other revenue \| TPC, formerly known as Mitsubishi Tanabe Pharma
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	2,794	2,612	5,735
License, collaboration and other revenue \| JT and Torii
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	5,659	5,366	5,394
License, collaboration and other revenue \| Otsuka
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 0	$ 0	$ 2,225

- Definition

+ References

+ Details

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Current assets:
Cash and cash equivalents	$ 184,844	$ 51,870
Inventories	15,610	16,243
Accounts receivable, net	47,031	34,368
Prepaid expenses and other current assets	5,470	11,350
Total current assets	252,955	113,831
Property and equipment, net	1,222	2,200
Operating right-of-use assets	3,663	8,218
Goodwill	59,044	59,044
Other long-term assets	59,681	37,377
Total assets	376,565	220,670
Current liabilities:
Accounts payable	21,185	15,180
Accrued expenses and other current liabilities	121,716	63,460
Short-term deferred revenue	2,681	0
Working Capital Fund liability, current portion	17,356	2,274
Total current liabilities	162,938	80,914
Long-term operating lease liabilities	0	3,547
Long-term debt, net	48,250	38,693
Liability related to settlement royalties, net of current portion	54,750	46,697
Liability related to sale of future royalties, net of current portion	50,608	52,066
Working Capital Fund liability, net of current portion	22,606	38,013
Warrant liability	2,980	5,176
Other long-term liabilities	1,823	4,749
Total liabilities	343,955	269,855
Commitments and contingencies (Note 10)
Stockholders' equity (deficit):
Preferred stock $0.00001 par value, 25,000,000 shares authorized; no shares issued and outstanding at December 31, 2025 and 2024	0	0
Common stock: $0.00001 par value; 350,000,000 shares authorized at December 31, 2025 and 2024; 265,424,818 and 224,848,992 shares issued and outstanding at December 31, 2025 and 2024, respectively	2	2
Additional paid-in capital	1,716,307	1,629,167
Accumulated other comprehensive income	6	6
Accumulated deficit	(1,683,705)	(1,678,360)
Total stockholders' equity (deficit)	32,610	(49,185)
Total liabilities and stockholders' equity (deficit)	$ 376,565	$ 220,670

LICENSE, COLLABORATION AND OTHER REVENUE

12 Months Ended

Dec. 31, 2025

Organization, Consolidation and Presentation of Financial Statements [Abstract]

LICENSE, COLLABORATION AND OTHER REVENUE

The Company recognized the following revenues from its license, collaboration and other revenue agreements (in thousands):


		Years Ended December 31,
Entity	Description	2025		2024		2023
Medice	License and Product Supply of Vafseo in EU	$	411	$	22	$	10,968
TPC, formerly known as Mitsubishi Tanabe Pharma	License and Product Supply of Vafseo in Japan	2,794		2,612		5,735
JT and Torii	License and royalties related to the sale of Riona in Japan	5,659		5,366		5,394
Otsuka	Terminated U.S. and International Agreements	—		—		2,225
Total License, Collaboration and Other Revenue		$	8,864	$	8,000	$	24,322

The following table presents changes in the Company’s contract assets and liabilities related to license, collaboration and other revenue agreements (in thousands):


	Year Ended December 31, 2025
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable(1)	$	2,010	$	8,894	$	(8,513)	$	2,391
Contract liability:
Deferred revenue	$	—	$	—	$	—	$	—

	Year Ended December 31, 2024
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable(1)	$	3,333	$	8,562	$	(9,885)	$	2,010
Contract liabilities:
Deferred revenue (long-term)(2)	$	43,296	$	—	$	(43,296)	$	—

(1)Excludes accounts receivable from product sales of Auryxia and Vafseo which are included in the accompanying consolidated balance sheets as of December 31, 2025 and 2024.

(2)See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for further information.

During the years ended December 31, 2025, 2024 and 2023, the Company recognized the following revenues as a result of changes in the contract asset and contract liability balances in the respective periods (in thousands):


	Years Ended December 31,
Revenue Recognized in the Period from:	2025		2024		2023
Deferred revenue - beginning of the period	$	—	$	—	$	3,738

During each of the years ended December 31, 2025, 2024 and 2023, the Company recognized no revenue from performance obligations satisfied in previous periods.

Medice License Agreement

On May 24, 2023, or the Medice Effective Date, the Company and MEDICE Arzneimittel Pütter GmbH & Co. KG, or Medice, entered into a License Agreement, or the Medice License Agreement, pursuant to which the Company granted to Medice an exclusive license to develop and commercialize Vafseo for the treatment of anemia in adult patients with CKD in the EEA, the UK, Switzerland and Australia, or collectively, the Medice Territory.

Under the Medice License Agreement, the Company received an up-front payment of $10.0 million and is eligible to receive the following payments:

(i) commercial milestone payments up to an aggregate of $100.0 million, and

(ii) tiered royalties ranging from 10% to 30% of Medice's annual net sales of Vafseo in the Medice Territory, subject to reduction in certain circumstances.

The royalties will expire on a country-by-country basis upon the latest to occur of (a) the date of expiration of the last-to-expire valid claim of any Company, Medice or joint patent that covers Vafseo in such country in the Medice Territory, (b) the date of expiration of data or regulatory exclusivity for Vafseo in such country in the Medice Territory and (c) the date that is twelve years from first commercial sale of Vafseo in such country in the Medice Territory.

Under the Medice License Agreement, the Company retains the right to develop Vafseo for non-dialysis patients with anemia due to CKD in the Medice Territory. If the Company develops Vafseo for non-dialysis patients and Vafseo receives marketing approval in the Medice Territory, Medice will commercialize Vafseo for both indications in the Medice Territory. In this instance, the Company would receive 70% of the net product margin of any sales of Vafseo in the non-dialysis patient population, unless Medice requests to share the cost of the development necessary to gain approval to market Vafseo for non-dialysis patients in the Medice Territory and the parties agree on alternative financial terms. If the Company develops

Vafseo for non-dialysis patients, the Company has determined that the activities under the Medice License Agreement represent joint operating activities in which both parties are active participants and of which both parties are exposed to significant risks and rewards that are dependent on the success of the activities. Accordingly, if the Company develops Vafseo for non-dialysis patients the Company will account for the joint activities in accordance with ASC No. 808, Collaborative Arrangements, or ASC 808. Additionally, the Company has determined that in the context of the development of Vafseo for non-dialysis patients, Medice does not represent a customer as contemplated by ASC 606. As a result, the activities conducted pursuant to development activities for Vafseo for non-dialysis patients will be accounted for as a component of the related expense in the period incurred.

The Medice License Agreement expires on the date of expiration of all payment obligations due thereunder with respect to Vafseo in the last country in the Medice Territory, unless earlier terminated in accordance with the terms of the Medice License Agreement. Either party may, subject to a cure period, terminate the Medice License Agreement in the event of the other party's uncured material breach. Medice has the right to terminate the Medice License Agreement in its entirety for convenience upon twelve months' prior written notice delivered on or after the date that is twelve months after the Medice Effective Date.

The Company evaluated the elements of the Medice License Agreement in accordance with the provisions of ASC 606 and concluded Medice is a customer. The Company identified one performance obligation in connection with its obligations under the Medice License Agreement, which is the license, or License Performance Obligation. The transaction price at inception was comprised of the up-front payment of $10.0 million, of which the Company received $8.6 million during the quarter ended June 30, 2023. The remaining $1.4 million was withheld by the German Federal Tax Office and was included in prepaid expenses and other current assets as of December 31, 2024 in the consolidated balance sheet. The $1.4 million was received during the year ended December 31, 2025.

Pursuant to the terms of the Medice License Agreement, the up-front payment of $10.0 million is non-refundable and non-creditable against any other amount due to the Company and was allocated to the License Performance Obligation, which was satisfied as of the Medice Effective Date. As such, the Company recognized the $10.0 million up-front payment as license, collaboration and other revenue in the consolidated statement of operations and comprehensive loss during the year ended December 31, 2023.

In accordance with ASC 606, the Company will recognize sales-based royalties and milestone payments at the later of when the performance obligation is satisfied or the related sales occur. During the years ended December 31, 2025, 2024 and 2023, the Company recognized $0.1 million in revenue from Medice royalties, immaterial revenue from Medice royalties and no revenue from Medice royalties, respectively. As of December 31, 2025, there were $0.1 million contract assets, and no accounts receivable, payables or deferred revenue in connection with the Medice License Agreement.

Medice Letter Agreement

On December 6, 2023, the Company and Medice entered into a letter agreement, or the Medice Letter Agreement, pursuant to which the Company agreed to sell to Medice a partial batch of Vafseo in order to achieve packaging validation for the Medice Territory. The Company previously recognized revenue under this arrangement when risk of loss passed to Medice and delivery occurred. During the year ended December 31, 2023, the Company recognized $1.0 million in collaboration, license and other revenue under the Medice Letter Agreement.

Supply of Drug Product to Medice

On September 13, 2024, the Company and Medice entered into a supply agreement, or the Medice Supply Agreement, under which the Company supplies Vafseo drug product to Medice for commercial and developmental use in the Medice Territory. The Company recognizes revenue under this arrangement when risk of loss passes to Medice, delivery has occurred, and Medice has accepted the product. The Company recognized $0.3 million of revenue under the Medice Supply Agreement during the year ended December 31, 2025. The Company did not recognize any revenue under the Medice Supply Agreement during the years ended December 31, 2024 or 2023. As of December 31, 2025, there were $0.3 million accounts receivable and no contract assets, payables or deferred revenue in connection with the Medice Supply Agreement.

Supply of Drug Substance to Medice

On November 12, 2025, the Company and Medice entered into Amendment #1 to the License Agreement, or the Medice Amendment. Pursuant to the Medice Amendment, the Company agreed to supply vadadustat drug substance to Medice pursuant to the terms of a supply agreement dated concurrently with the Medice Amendment and granted Medice the right to manufacture Vafseo tablets using the vadadustat drug substance to be supplied by the Company. In addition, the Medice Amendment provides that any know-how or patent rights arising out of Medice’s manufacture of Vafseo tablets will be owned by the Company.

The Company did not recognize any revenue related to the supply of vadadustat drug substance to Medice during the years ended December 31, 2025, 2024 or 2023.

TPC Collaboration Agreement

On December 11, 2015, the Company and TPC entered into the TPC Agreement, providing TPC with exclusive development and commercialization rights to Vafseo in the TPC Territory, which was amended effective as of December 2, 2022. In addition, the Company supplies Vafseo to TPC for both clinical and commercial use in the TPC Territory. In February 2021, the Company entered into the Royalty Agreement with HCR, whereby the Company sold its right to receive royalties and sales milestones under the TPC Agreement, subject to certain caps and other terms and conditions. See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for more information.

Unless earlier terminated, the TPC Agreement will continue in effect on a country-by-country basis until the later of the following: expiration of the last-to-expire patent covering Vafseo in such country in the TPC Territory; expiration of marketing or regulatory exclusivity in such country in the TPC Territory; or ten years after the first commercial sale of Vafseo in such country in the TPC Territory. TPC may terminate the TPC Agreement upon twelve months’ notice at any time after the second anniversary of the effective date of the TPC Agreement. Either party may terminate the TPC Agreement upon the material breach of the other party that is not cured within a specified time period or upon the insolvency of the other party.

Under the TPC Agreement, TPC is required to make certain milestone payments to the Company aggregating up to approximately $225.0 million upon the achievement of specified development, regulatory and commercial events. The Company has received $10.0 million in development milestone payments. Of the $40.0 million in regulatory milestone payments the Company is eligible for, the Company received $10.0 million in relation to the Japanese NDA filing in the third quarter of 2019 and $15.0 million following regulatory approval of Vafseo in Japan in the third quarter of 2020. The Company is also entitled to receive up to $175.0 million in commercial milestone payments associated with aggregate sales of all products. In consideration for the exclusive license and other rights contained in the TPC Agreement, TPC made a $20.0 million upfront payment as well as a $20.5 million payment for Phase 2 studies in Japanese patients completed by the Company and reimbursed by TPC. Additionally, the Company is entitled to receive tiered royalty payments ranging from 13% to 20% of annual net sales of Vafseo in the TPC Territory, subject to reduction in certain circumstances.

The Company evaluated the elements of the TPC Agreement in accordance with the provisions of ASC 606 and concluded that the contract counterparty, TPC, is a customer. The Company identified two performance obligations in connection with its material promises under the TPC Agreement as follows: (i) License, Research and Clinical Supply Performance Obligation and (ii) Rights to Future Know-How Performance Obligation.

The transaction price was comprised of: (i) the up-front payment of $20.0 million, (ii) the cost for the Phase 2 studies of $20.5 million, (iii) the cost of all clinical supply provided to TPC for the Phase 3 studies, (iv) $10.0 million in development milestones received, (v) $25.0 million in regulatory milestones received and (vi) $8.7 million in royalties from net sales of Vafseo. The Company re-evaluates the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. As of December 31, 2025, all development milestones and $25.0 million in regulatory milestones have been achieved. No other regulatory milestones or commercial milestones have been assessed as probable and have been fully constrained until the period in which they are achieved.

The Company allocates the transaction price to each performance obligation based on the Company’s best estimate of the relative standalone selling price. The Company developed a best estimate of the standalone selling price for the Rights to Future Know-How Performance Obligation primarily based on the likelihood that additional intellectual property covered by the license conveyed will be developed during the term of the arrangement and determined it is immaterial. As such, the Company did not develop a best estimate of standalone selling price for the License, Research and Clinical Supply Performance Obligation and allocated the entire transaction price to this performance obligation.

Revenue for the License, Research and Clinical Supply Performance Obligation for the TPC Agreement is being recognized using a proportional performance method, for which all deliverables have been completed. The Company recognizes any revenue from TPC royalties in the period in which the sales occur. The Company recognized revenue from TPC royalties of $1.8 million, $1.9 million and $2.0 million during the years ended December 31, 2025, 2024 and 2023, respectively. As noted above, in February 2021, the Company entered into the Royalty Agreement, whereby the Company sold its right to receive these royalties and sales milestones under the TPC Agreement, subject to certain caps and other conditions. See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for more information. The revenue is classified as collaboration, license and other revenue in the accompanying consolidated statements of operations and comprehensive loss. As of December 31, 2025, there were no accounts receivable, payables or deferred revenue and $0.5 million in contract assets recorded in connection with the TPC Agreement.

Supply of Drug Product to TPC

On July 15, 2020, the Company and TPC entered into a supply agreement, or the TPC Supply Agreement, under which the Company supplies Vafseo drug product to TPC for commercial use in Japan and certain other Asian countries, as contemplated by the TPC Agreement. The term of the TPC Supply Agreement extends throughout the term of the TPC Agreement, and the termination provisions of the TPC Agreement govern termination of the TPC Supply Agreement.

On December 16, 2022, the Company, TPC and Esteve executed an Assignment of Supply Agreement, or the Esteve Assignment Agreement, pursuant to which the rights and obligations of the Company under the Esteve Agreement were transferred to TPC. The Company has no further obligation to take delivery of, or pay for, product delivered by Esteve except as disclosed in Note 10, Commitments and Contingencies.

The Company does not recognize revenue under this arrangement until risk of loss on the drug product passes to TPC and delivery has occurred and TPC has accepted the product. During the years ended December 31, 2025, 2024 and 2023, the Company recognized $1.0 million, $0.7 million and $3.7 million of revenue, respectively, under the TPC Supply Agreement. As of December 31, 2025, there were no accounts receivable, deferred revenue or other current liabilities relating to the TPC Supply Agreement.

JT and Torii Sublicense Agreement

The Company has an Amended and Restated Sublicense Agreement, which was amended in June 2013, with JT and Torii, or the JT and Torii Sublicense Agreement, under which JT and Torii obtained the exclusive sublicense rights for the development and commercialization of ferric citrate hydrate in Japan. JT and Torii are responsible for the future development and commercialization costs in Japan.

The Company is eligible to receive royalty payments based on a tiered low double-digit percentage of net sales of Riona in Japan inclusive of amounts that the Company must pay to Panion on JT and Torii's net sales of Riona under the Panion License Agreement subject to certain reductions upon expiration or termination of the Amended and Restated License Agreement between the Company and Panion, pursuant to which Company in-licensed the exclusive worldwide rights, excluding certain Asian-Pacific countries, for the development and commercialization of ferric citrate. The Company is entitled to receive up to an additional $55.0 million upon the achievement of certain annual net sales milestones.

The sublicense under the JT and Torii Sublicense Agreement terminates upon the expiration of all underlying patent rights. Also, JT and Torii may terminate the JT and Torii Sublicense Agreement with or without cause upon at least six months' prior written notice to the Company. Additionally, either party may terminate the JT and Torii Sublicense Agreement for cause upon 60 days’ prior written notice after the breach of any uncured material provision of the JT and Torii Sublicense Agreement, or after certain insolvency events.

The Company evaluated the elements of the JT and Torii Sublicense Agreement in accordance with the provisions of ASC 606 and concluded that the contract counterparty, JT and Torii, is a customer. The Company identified two performance obligations in connection with its obligations under the JT and Torii Sublicense Agreement: (i) License and Supply Performance Obligation and (ii) Rights to Future Know-How Performance Obligation. The Company developed a best estimate of the standalone selling price for the Rights to Future Know-How Performance Obligation primarily based on the likelihood that additional intellectual property covered by the license conveyed will be developed during the term of the arrangement and determined it immaterial. As such, the Company did not develop a best estimate of standalone selling price for the License and Supply Performance Obligation and allocated the entire transaction price to this performance obligation. Additionally, as of the consummation of the Merger, the services associated with the License and Supply Performance Obligation were completed and JT and Torii had secured their own source to manufacture ferric citrate hydrate. As such, any initial license fees as well as any development-based milestones and manufacturing fee revenue were received and recognized prior to the Merger. The Company determined that the remaining consideration that may be payable to the Company under the terms of the sublicense agreement are either quarterly royalties on net sales or payments due upon the achievement of sales-based milestones. In accordance with ASC 606, the Company recognizes sales-based royalties and milestone payments based on the level of sales, when the related sales occur as these amounts have been determined to relate predominantly to the license granted to JT and Torii and therefore are recognized at the later of when the performance obligation is satisfied, or the related sales occur.

During the years ended December 31, 2025, 2024 and 2023, the Company recognized license revenue of $5.7 million, $5.4 million and $5.4 million related to royalties earned on net sales of Riona in Japan, respectively. The Company records the associated mid-single digit percentage of net sales royalty expense due to Panion, the licensor of Riona, in the same period as the royalty revenue from JT and Torii is recorded. As of December 31, 2025, there was $1.5 million in accounts receivables relating to the JT and Torii Sublicense Agreement.

Prior Collaboration and License Agreements

U.S. Collaboration and License Agreement with Otsuka Pharmaceutical Co. Ltd.

On December 18, 2016, the Company entered into a collaboration and license agreement, or Otsuka U.S. Agreement, with Otsuka Pharmaceutical Co. Ltd, or Otsuka. The collaboration was focused on the development and commercialization of Vafseo in the U.S.

On May 12, 2022, the Company received notice from Otsuka that Otsuka had elected to terminate the Otsuka U.S. Agreement and the April 25, 2017 collaboration and license agreement with Otsuka, or Otsuka International Agreement. On June 30, 2022, the Company and Otsuka entered into the Termination and Settlement Agreement, or Otsuka Termination Agreement, pursuant to which, among other things, the Company and Otsuka agreed to terminate the Otsuka U.S. Agreement and the Otsuka International Agreement as of June 30, 2022.

During the year ended December 31, 2023, the Company recognized $2.2 million in collaboration, license and other revenue in connection with the Packaging Validation Transfer Agreement entered into with Otsuka on April 20, 2023. Under the Packaging Validation Transfer Agreement, the parties agreed that responsibility for all remaining packaging validation activities would be transferred from Otsuka to the Company in consideration of payments made by Otsuka to the Company. The Company evaluated the agreement under ASC 606 and concluded it was closely tied to the prior collaboration, license and other revenue agreements and under ASC 606 recognized collaboration, license and other revenue during the year ended December 31, 2023.

NET LOSS PER SHARE (Details) - shares	12 Months Ended
NET LOSS PER SHARE (Details) - shares	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	26,590,872	25,191,038	17,256,104
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	2,115,385	3,076,923	0
Outstanding common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	17,516,945	16,049,012	12,690,624
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	6,323,229	5,429,790	3,930,167
Stock appreciation rights
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	635,313	635,313	635,313

LIABILITY RELATED TO SETTLEMENT ROYALTIES, WORKING CAPITAL FUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES

12 Months Ended

Dec. 31, 2025

Other Liabilities Disclosure [Abstract]

Vifor License Agreement

Summary of Agreement

On February 18, 2022, the Company entered into a Second Amended and Restated License Agreement, or the Vifor License Agreement, with CSL Vifor, which amended and restated the License Agreement dated as of May 12, 2017, or the Original License Agreement. The Vifor License Agreement granted CSL Vifor an exclusive license to sell Vafseo to Fresenius Medical Care North America and its affiliates, including Fresenius Kidney Care Group LLC, to certain third-party dialysis organizations approved by the Company, to independent dialysis organizations that were members of certain group purchasing organizations and certain non-retail specialty pharmacies, collectively, the Supply Group, in the U.S.

The Vifor License Agreement was structured as a profit share arrangement between the Company and CSL Vifor in which the Company would receive approximately 66% of the profit, net of certain pre-specified costs. In addition, CSL Vifor made an upfront payment to the Company of $25.0 million in February 2022 in connection with the amendment and restatement of the Vifor License Agreement, which was previously recorded as long-term deferred revenue in the consolidated balance sheets.

Investment Agreements

In connection with the Original License Agreement, in May 2017, the Company sold an aggregate of 3,571,429 shares of the Company’s common stock, or 2017 Shares, to CSL Vifor at a price per share of $14.00 for a total of $50.0 million.

In February 2022, in connection with the Vifor License Agreement, the Company sold an aggregate of 4,000,000 shares of its common stock, or 2022 Shares, to CSL Vifor at a price per share of $5.00 for a total of $20.0 million.

The $18.3 million, which represented the premiums over the closing stock price, or $4.7 million for the 2017 Shares and $13.6 million for the 2022 Shares, was previously recorded as long-term deferred revenue in the consolidated balance sheets as it represented consideration related to the Vifor License Agreement.

The 2017 Shares and 2022 Shares are subject to standstill agreements and are subject to voting agreements. The 2017 Shares and 2022 Shares have not been registered pursuant to the Securities Act of 1933, as amended, or the Securities Act, and were issued and sold in reliance upon the exemption from registration contained in Section 4(a)(2) of the Securities Act and Rule 506 promulgated thereunder as the transaction did not involve any public offering within the meaning of Section 4(a)(2) of the Securities Act.

Vifor Termination Agreement

On July 10, 2024, the Company and CSL Vifor entered into the Vifor Termination Agreement, pursuant to which the Company and CSL Vifor agreed, among other things, to terminate, effective immediately, the Vifor License Agreement.

Pursuant to the terms of the Vifor Termination Agreement, the Company will pay CSL Vifor decreasing quarterly tiered royalty payments ranging from a high single-digit percentage of the Company’s net sales of Vafseo up to $450.0 million to mid-single digit percentage of the Company’s net sales of Vafseo above $450.0 million, in each case, in the U.S. during a calendar year, or the Settlement Royalty Payments. The Settlement Royalty Payments commenced upon the first sale of Vafseo by the Company to a third party for use in the U.S., and will continue until the later of the (i) expiration of the last-to-expire valid claim listed in the FDA Orange Book that would be infringed by the making, using, selling or importing of Vafseo in the U.S. or (ii) the expiration of marketing or regulatory exclusivity for Vafseo in the U.S., or the Settlement Royalty Term. Beginning on July 1, 2027 and throughout the Settlement Royalty Term, the Company has the option to make a one-time payment to CSL Vifor, or the Royalty Buy-Down Option, upon which the Settlement Royalty Payments will be adjusted as of the date of exercise of the Royalty Buy-Down Option such that the Company will then only pay CSL Vifor quarterly royalty payments based on a mid-single digit percentage of the Company’s net sales of Vafseo up to $450.0 million in the U.S. during a calendar

year in lieu of the above Settlement Royalty Payments. If the Company exercises the Royalty Buy-Down Option, the WCF Royalty Payments, as described below, will continue as described above.

The WCF Royalty Payments, as described below, the Settlement Royalty Payments and the Royalty Buy-Down Option are in consideration for the termination of the Vifor License Agreement and all obligations thereunder, and the covenants and agreements set forth in the Vifor Termination Agreement, including the settlement and release of all disputes and claims arising from the Vifor License Agreement.

As a result of the Vifor Termination Agreement, the Company reassessed whether the Vifor License Agreement still met the criteria to be considered a contract within the scope of ASC 606, Revenue from Contracts with Customers, and concluded that CSL Vifor no longer met the definition of a customer and, therefore, the arrangement should not be considered a revenue contract with a customer under ASC 606. The Company therefore determined that the consideration received from CSL Vifor of $43.3 million, comprised of the up-front payment of $25.0 million and the premiums paid by CSL Vifor for the 2017 Shares and 2022 Shares of $4.7 million and $13.6 million, respectively, should be classified as debt. Accordingly, the Company recorded the $43.3 million as a liability and is amortizing such amount using the effective interest method over the Settlement Royalty Term. The liability related to settlement royalties and the amortization are based on the Company’s current estimates of future royalties expected to be paid over the life of the arrangement. To the extent the Company’s estimates of future royalty payments are greater or less than previous estimates or the estimated timing of such payments is materially different than previous estimates, the Company will adjust the effective interest rate and recognize the related non-cash interest expense on a prospective basis. On a quarterly basis, the Company reassesses the expected royalty payments.

The annual effective interest rate as of December 31, 2025 was 22.3% which is reflected as interest expense in the consolidated statements of operations and comprehensive loss. The Company recognized interest expense of $18.4 million and $9.3 million for the years ended December 31, 2025 and 2024, respectively, related to the settlement royalties liability. As of December 31, 2025 and 2024, the balances related to the settlement royalties liability were as follows (in thousands):


	December 31,
Description	2025		2024
Current portion (included in accrued expenses and other current liabilities)	$	12,516	$	5,924
Long-term portion	54,750		46,697
Total settlement royalties liability	$	67,266	$	52,621

Working Capital Fund Liability (Previously Referred to as Refund Liability to Customer)

Pursuant to the Vifor License Agreement, CSL Vifor contributed $40.0 million to a working capital fund, or Working Capital Fund, established to partially fund the Company’s costs of purchasing Vafseo from its contract manufacturers.

The Working Capital Fund is considered a debt arrangement with zero coupon interest and the Company imputes interest on the Working Capital Fund liability at a rate of 15.0% per annum, which was determined based on certain factors, including the Company's credit rating, comparable securities yield and the expected repayment period. On March 18, 2022, when the $40.0 million was received from CSL Vifor, the Company recorded an initial discount on the Working Capital Fund liability and a corresponding deferred gain to the Working Capital Fund liability in the consolidated balance sheet.

On May 3, 2024, the Company and CSL Vifor entered into Amendment #1 to the Vifor License Agreement, or the Amendment. Pursuant to the Amendment, and as modified by the Vifor Termination Agreement, the Company and CSL Vifor agreed to modify the method of repayment of the Working Capital Fund such that the Working Capital Fund will be repaid through quarterly tiered royalty payments ranging from 8% to 14% of the Company's net sales of Vafseo in the U.S., or the WCF Royalty Payments. The WCF Royalty Payments commenced on July 1, 2025, and will continue until the earlier of (i) the cumulative total of the WCF Royalty Payments equals $40.0 million, or (ii) May 31, 2028, or the WCF Royalty Term. The WCF Royalty Payments are subject to minimum true-up milestones of $10.0 million, $20.0 million and $40.0 million, or the WCF Royalty True-Up Payments, on each of May 31, 2026, May 31, 2027 and May 31, 2028, respectively, or the WCF Royalty True-Up Dates. If the cumulative total of the WCF Royalty Payments paid to CSL Vifor on any given WCF Royalty True-Up Date is less than the respective WCF Royalty True-Up Payment, the Company will pay CSL Vifor a one-time payment equal to the difference between the WCF Royalty True-Up Payment and the cumulative total of the WCF Royalty Payments paid by the Company through such WCF Royalty True-Up Date. The Company determined that the terms of the Amendment are not substantially different than the terms of the Vifor License Agreement, and therefore the Amendment was accounted for as a modification. The Company concluded that the 15% discount rate remains appropriate. On a quarterly basis, the Company reassesses the effective rate and will adjust the rate prospectively, if needed.

The discount on the Working Capital Fund liability is being amortized to interest expense using the effective interest method over the WCF Royalty Term. The deferred gain is being amortized to interest income on a straight-line basis over the WCF

Royalty Term. The amortization of the discount was $4.7 million, $3.8 million and $3.1 million for the years ended December 31, 2025, 2024 and 2023, respectively. The amortization of the deferred gain was $3.9 million, $3.6 million and $4.0 million for the years ended December 31, 2025, 2024 and 2023, respectively.

As of December 31, 2025 and 2024, the balances related to the Working Capital Fund liability were as follows (in thousands):


	December 31,
Description	2025		2024
Current portion	$	17,356	$	2,274
Long-term portion	22,606		38,013
Total Working Capital Fund liability	$	39,962	$	40,287

Liability Related to Sale of Future Royalties

In February 2021, the Company entered into a royalty interest acquisition agreement, or the Royalty Agreement, with HealthCare Royalty Partners IV, L.P., or HCR, pursuant to which the Company sold to HCR its right to receive royalties and sales milestones for Vafseo in Japan and certain other Asian countries, such countries collectively, the TPC Territory, and such payments collectively the Royalty Interest Payments, in each case, payable to the Company under the Company's Collaboration Agreement, or the TPC Agreement, with Tanabe Pharma Corporation, or TPC. The Royalty Interest Payments are subject to an annual maximum “cap” of $13.0 million, after which the Company will receive 85% of the Royalty Interest Payments for the remainder of that year. The Royalty Interest Payments are also subject to an aggregate maximum “cap” of $150.0 million, after which the Royalty Interest Payments will revert back to the Company.

The Company retains the right to receive all potential future regulatory milestones for Vafseo under the TPC Agreement. The Royalty Agreement will terminate on the earlier of the date on which HCR has received (i) the last Royalty Interest Payment or (ii) payment by the Company of an amount equal to the Aggregate Cap minus the aggregate amount of all Royalty Interest Payments actually received by HCR.

At the transaction date, the Company recognized the proceeds received from HCR of $44.8 million (net of certain transaction expenses) as a liability and is amortizing it using the effective interest method over the life of the arrangement. The liability related to sale of future royalties and the debt amortization are based on the Company’s current estimates of future royalties expected to be paid over the life of the arrangement. To the extent the Company’s estimates of future royalty payments are greater or less than previous estimates or the estimated timing of such payments is materially different than previous estimates, the Company will adjust the effective interest rate and recognize related non-cash interest expense on a prospective basis. In the event the Company's estimates of future royalties are less than the proceeds from the sale of future royalties, the Company will not recognize related non-cash interest expense. On a quarterly basis, the Company assesses the expected royalty payments. The annual effective interest rate as of December 31, 2025 was 0% and, therefore the Company did not recognize any non-cash interest expense in the consolidated statements of operations and comprehensive loss. As a result of the Company's ongoing involvement in the cash flows related to the royalties and sales milestones in the TPC Territory, the Company will continue to account for the royalties received as non-cash royalty revenue which is reflected within license, collaboration and other revenue in the consolidated statements of operations and comprehensive loss.

During the years ended December 31, 2025, 2024 and 2023, the Company paid $1.8 million, $2.0 million and $2.0 million of royalties to HCR, respectively. As of December 31, 2025 and 2024, the balances related to the liability related to the sale of future royalties were as follows (in thousands):


	December 31,
Description	2025		2024
Current portion (included in accrued expenses and other current liabilities)	$	1,664	$	2,039
Long-term portion	50,608		52,066
Total liability related to sale of future royalties	$	52,272	$	54,105

The Royalty Agreement requires the Company to take certain actions, including actions with respect to the Royalty Interest Payments, the TPC Agreement, and the Company's intellectual property. The Royalty Agreement also contains certain representations and warranties, covenants, indemnification obligations, events of default and other provisions that are customary for a royalty monetization transaction of this nature. In addition, the Company granted HCR a precautionary security interest in connection with the Royalty Interest Payments.

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2025
Audit Information [Abstract]
Auditor Name	Ernst & Young LLP
Auditor Location	Boston, Massachusetts
Auditor Firm ID	42

LICENSE, COLLABORATION AND OTHER REVENUE - Schedule of Revenue Recognized Resulting from Changes in Contract Asset and Contract Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue - beginning of the period	$ 0	$ 0	$ 3,738

INVENTORIES - Schedule of Components Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Inventory [Line Items]
Inventories, current	$ 15,610	$ 16,243
Inventories, long-term	59,129	34,953
Total inventories	74,739	51,196
Inventories
Inventory [Line Items]
Work-in-process	12,651	12,031
Finished goods	2,959	4,212
Other Noncurrent Assets
Inventory [Line Items]
Work-in-process	57,290	34,572
Finished goods	1,789	0
Raw materials	$ 50	$ 381

INDEBTEDNESS - Narrative (Details) $ / shares in Units, $ in Thousands				12 Months Ended
	Feb. 03, 2025 USD ($)	Apr. 19, 2024 USD ($)	Jan. 29, 2024 USD ($) tranche $ / shares shares	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jul. 23, 2025 shares	Jul. 21, 2025 $ / shares shares	Feb. 28, 2025 $ / shares shares	Nov. 11, 2019 USD ($)
Line of Credit Facility [Line Items]
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]			Secured Overnight Financing Rate (SOFR) [Member]
Warrant to purchase common stock (in shares) \| shares			3,076,923				1,408,588	2,115,384	1,153,846
Exercise price (in dollars per share) \| $ / shares			$ 1.30					$ 1.30	$ 1.30
Warrant exercise period (in years)									8 years
Warrant liability				$ 2,980	$ 5,176
Loss on extinguishment of debt				$ 0	517	$ 0
Secured Debt \| Term Loan Facility \| Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity			$ 55,000
Line of credit, maximum borrowing capacity, number of available tranches \| tranche			3
Variable rate, floor (as percent)			4.25%
Basis spread on variable rate (as percent)			6.75%
Debt instrument, cap rate (as percent)			15.00%
Debt instrument, interest rate (as percent)				11.00%
Interest expense				$ 8,400	7,100
Annual interest rate, increase (as percent)			3.00%
Late fee percentage			2.00%
Exit fee percentage			0.75%
Debt covenant, cash and cash equivalents			$ 15,000
Debt covenant, revenue period (in months)			12 months
Debt covenant, revenue			$ 150,000
Secured Debt \| Term Loan Facility \| Line of Credit \| Minimum
Line of Credit Facility [Line Items]
Transaction fee percentage			1.00%
Prepayment fee percentage			1.00%
Secured Debt \| Term Loan Facility \| Line of Credit \| Maximum
Line of Credit Facility [Line Items]
Transaction fee percentage			1.25%
Prepayment fee percentage			4.00%
Secured Debt \| Term Loan Facility, Tranche A \| Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity			$ 37,000
Proceeds from line of credit			34,500
Secured Debt \| Term Loan Facility, Tranche B \| Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity		$ 8,000
Proceeds from line of credit		$ 7,500
Secured Debt \| Term Loan Facility, Tranche C \| Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 10,000
Proceeds from line of credit	$ 9,300
Term Loan \| Tranche A and B \| Keryx \| Biopharma Credit Investments V (Master) LP \| Collateral Agent, Pharmakon
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity										$ 100,000
Interest expense					0	$ 6,000
Extinguishment of debt			35,000
Payment of outstanding debt interest and prepayment fee			$ 200
Loss on extinguishment of debt					$ 500

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - Narrative (Details) $ in Thousands		12 Months Ended
	Jun. 06, 2019 USD ($) shares	Dec. 31, 2025 USD ($) installment age shares	Dec. 31, 2024 USD ($) shares	Dec. 31, 2023 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 11,283	$ 7,775	$ 9,317
Granted (in shares) \| shares		5,464,077
Number of options outstanding (in shares) \| shares		18,152,258	16,684,325
Options exercised, aggregate intrinsic value		$ 1,800	$ 400	0
Fair value of options vested		4,300	3,700	6,400
Unrecognized compensation costs, options		$ 11,200
Unrecognized compensation costs, options, period for recognition (in years)		2 years 7 months 20 days
Employees eligibility age to participate in retirement plan \| age		21
Employers contributions to defined contribution plan		$ 1,900	1,700	1,700
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 168	$ 84	73
Purchase price at the end of offering period	85.00%
Offering period (in months)	6 months
Maximum employee subscription rate (as percent)	15.00%
Maximum employee subscription amount	$ 25
Maximum number of shares per employee in offering period \| shares	1,500
Common stock, shares reserved for future issuance (in shares) \| shares		4,260,647	4,448,069
Number of shares issued (in shares) \| shares		187,422
Share-based Payment Arrangement, Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 5,356	$ 4,036	5,310
Expiration period (in years)		10 years
Share-based Payment Arrangement, Option \| Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		100.00%
Share-based Payment Arrangement, Option \| Share Based Compensation Award Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Vesting percentage		25.00%
Share-based Payment Arrangement, Option \| Share Based Compensation Award Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Number of equal quarterly installments \| installment		12
Share-based Payment Arrangement, Option \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		12 months
Share-based Payment Arrangement, Option \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		48 months
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period (in years)		10 years
Stock appreciation rights \| Share Based Compensation Award Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Vesting percentage		25.00%
Stock appreciation rights \| Share Based Compensation Award Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Number of equal quarterly installments \| installment		12
Stock appreciation rights \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		12 months
Stock appreciation rights \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		48 months
Inducement Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares		1,454,477
Number of options outstanding (in shares) \| shares		1,152,477
Inducement Award Program \| Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding (in shares) \| shares		3,034,085	2,534,775
Unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 5,214	$ 3,655	3,637
Unvested restricted stock units \| Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		100.00%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date, Subjected To Individual Continued Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche Two, Second Anniversary After Grant Date, Subjected To Individual Continued Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche Three, Third Anniversary After Grant Date, Subjected To Individual Continued Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche Two, Following First Anniversary After Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		2 years
Vesting percentage		66.67%
Number of equal quarterly installments \| installment		8
Award vesting grace period (in years)		1 year
Unvested restricted stock units \| Share Based Compensation Award Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		50.00%
Unvested restricted stock units \| Share Based Compensation Award Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		6 months
Vesting percentage		25.00%
Award vesting grace period (in years)		1 year
Restricted Stock Units (RSUs) And Performance Based Restricted Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs, options, period for recognition (in years)		1 year 8 months 23 days
Vested in period		$ 3,400	$ 3,200	$ 8,400
Unrecognized compensation costs, stock		$ 7,700
Employees \| Share-based Payment Arrangement, Option \| Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares		3,634,300
Director \| Share-based Payment Arrangement, Option \| Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares		375,200

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Allowance for Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 1,212	$ 1,029	$ 1,106
Provision for bad debts	1,479	877	(77)
Recoveries/(write-offs)	0	(695)	0
Ending balance	$ 2,691	$ 1,212	$ 1,029

INTANGIBLE ASSET AND GOODWILL	12 Months Ended
INTANGIBLE ASSET AND GOODWILL	Dec. 31, 2025
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSET AND GOODWILL	INTANGIBLE ASSET AND GOODWILL Intangible Asset The Company maintained a definite-lived intangible asset related to developed product rights for Auryxia. The intangible asset was initially recorded at fair value and was stated net of accumulated amortization. The Company amortized the intangible asset using the straight-line method over the estimated useful life of six years. The intangible asset was fully amortized as of December 31, 2024. The Company recorded $36.0 million in amortization expense during each of the years ended December 31, 2024 and 2023 related to the developed product rights for Auryxia. Goodwill As of December 31, 2025 and 2024, the Company had goodwill of $59.0 million recorded in connection with the December 2018 merger with Keryx Biopharmaceuticals, Inc., or Keryx. The Company has not identified any goodwill impairment to date.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2025

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation and Principles of Consolidation

Certain monetary amounts, percentages and other figures included elsewhere in these consolidated financial statements have been subject to rounding adjustments. Accordingly, figures shown as totals in certain tables may not be the arithmetic aggregation of the figures that precede them, and figures expressed as percentages in the text may not total 100% or, as applicable, when aggregated, may not be the arithmetic aggregation of the percentages that precede them.

Use of Estimates

Cash, Cash Equivalents and Restricted Cash


	December 31,
Reconciliation of cash, cash equivalents and restricted cash (in thousands)	2025		2024		2023
Cash and cash equivalents	$	184,844	$	51,870	$	42,925
Restricted cash	1,699		1,680		1,654
Total cash, cash equivalents and restricted cash	$	186,543	$	53,550	$	44,579

Fair Value of Financial Instruments

•Level 1 – unadjusted quoted prices in active markets for identical assets or liabilities to the reporting entity at the measurement date.

Accounts Receivable

Concentrations of Risk and Off-Balance Sheet Risk

Credit Risk

The following table summarizes the activity related to the Company's allowance for credit losses (in thousands):


	Year Ended December 31,
	2025		2024		2023
Beginning balance	$	1,212	$	1,029	$	1,106
Provision for bad debts	1,479		877		(77)
Recoveries/(write-offs)	—		(695)		—
Ending balance	$	2,691	$	1,212	$	1,029


	% of Total Gross Revenues
	Years Ended December 31,
Customer	2025	2024	2023
Fresenius Medical Care Rx	30%	48%	40%
U.S. Renal Care	29%	*	*
DaVita, Inc.	25%	*	*
Cencora, Inc.	*	19%	21%
McKesson Corporation	*	12%	11%
Cardinal Health, Inc.	*	*	10%


	% of Gross Accounts Receivable
	December 31,
Customer	2025	2024
U.S. Renal Care	42%	*
DaVita, Inc.	29%	16%
Fresenius Medical Care Rx	*	42%
Cencora, Inc.	*	13%

*Percentage less than 10% threshold.

Off-Balance Sheet Accounts

Manufacturing and Distribution Risk

Inventories, including Pre-Launch Inventories

Property and Equipment

Asset Category

Estimated Useful Life

Computer equipment and software

3 years

Furniture and fixtures

5 years

7 years

Laboratory and other equipment

7 years

Leasehold improvements

Shorter of the useful life or remaining lease term

Intangible Asset

Goodwill

Goodwill reflects the excess purchase price over the fair value of the net tangible and intangible assets acquired in a business combination.

Impairment of Long-Lived Assets and Intangible Asset Subject to Amortization

The Company did not recognize any impairment losses on long-lived assets for the years ended December 31, 2025, 2024 and 2023.

Leases

Liability Related to Sale of Future Royalties

Working Capital Fund Liability (Previously Referred to as Refund Liability to Customer)

Liability Related to Settlement Royalties

Warrant Liability

Excess Firm Purchase Commitment Liability

Revenue Recognition

(i)identify the contract(s) with a customer;

(ii)identify the performance obligations in the contract;

(iii)determine the transaction price;

(iv)allocate the transaction price to the performance obligations in the contract; and

(v)recognize revenue when (or as) the entity satisfies a performance obligation.

Product Revenue, Net

License, Collaboration and Other Revenues

Licenses of Intellectual Property

Milestone Payments

Drug Product Supply

Royalties

Collaborative Arrangements

Cost of Product and Other Revenue

Research and Development Expenses

Selling, General and Administrative Expenses

Patent Costs

Stock-Based Compensation

Income Taxes

Business Combinations and Asset Acquisitions

Net Loss per Share

Segment Information

New Accounting Pronouncements - Recently Adopted

New Accounting Pronouncements - Not Yet Adopted

currently evaluating ASU 2025-05 and does not expect it to have a material effect on the Company’s consolidated financial statements.

CAPITAL STOCK (Details) - USD ($) $ / shares in Units, $ in Millions				4 Months Ended	12 Months Ended
	Apr. 22, 2025	Mar. 19, 2025	Apr. 07, 2022	Dec. 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Jul. 23, 2025	Jul. 21, 2025	Feb. 28, 2025	Sep. 09, 2024	Jan. 29, 2024
Class of Stock [Line Items]
Common stock, authorized (in shares)				350,000,000	350,000,000	350,000,000
Common stock, par value (in dollars per share)				$ 0.00001	$ 0.00001	$ 0.00001
Common stock, outstanding (in shares)				224,848,992	265,424,818	224,848,992
Common stock, issued (in shares)				224,848,992	265,424,818	224,848,992
Preferred stock, authorized (in shares)				25,000,000	25,000,000	25,000,000
Preferred stock, par value (in dollars per share)				$ 0.00001	$ 0.00001	$ 0.00001
Preferred stock, outstanding (in shares)				0	0	0
Preferred stock, shares issued				0	0	0
Issuance and sale of equity securities											$ 75.0
Warrant to purchase common stock (in shares)								1,408,588	2,115,384	1,153,846		3,076,923
Exercise price (in dollars per share)									$ 1.30	$ 1.30		$ 1.30
Warrant exercise period (in years)										8 years
Warrant purchased (in shares)									2,115,384
Warrants issued (in shares)									1,408,588
Vifor (International) Ltd. \| License
Class of Stock [Line Items]
Unregistered stock held by customer (in shares)					7,571,429
At-The-Market Sale Agreement, Authorized April 2022
Class of Stock [Line Items]
Number of shares sold in offering (in shares)						13,261,311	6,189,974
Sale of stock, consideration received, gross						$ 19.2	$ 6.8
Aggregate net proceeds from offering						$ 18.7	$ 6.7
At-The-Market Sale Agreement, Authorized April 2022, Amended
Class of Stock [Line Items]
Number of shares sold in offering (in shares)				14,271,631	9,437,364
Sale of stock, consideration received, gross				$ 24.3	$ 18.7
Aggregate net proceeds from offering				$ 23.8	$ 18.4
Public Stock Offering
Class of Stock [Line Items]
Number of shares sold in offering (in shares)		25,000,000
Aggregate net proceeds from offering	$ 1.6	$ 46.5
Sale of stock, price per share (in dollars per share)		$ 2.00
Public Stock Offering - Underwriting Agreement
Class of Stock [Line Items]
Sale of stock, price per share (in dollars per share)		$ 1.88
Over-Allotment Option
Class of Stock [Line Items]
Number of shares sold in offering (in shares)	850,000	3,750,000
Underwriters allotment option, term (in days)		30 days
Maximum \| At-The-Market Sale Agreement, Authorized April 2022
Class of Stock [Line Items]
Common stock sales agreement amount			$ 26.0

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS

12 Months Ended

Dec. 31, 2025

Equity [Abstract]

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS

Stock-Based Compensation Plans

The Company incurred stock-based compensation expenses of $11.3 million, $7.8 million and $9.3 million for the years ended December 31, 2025, 2024 and 2023, respectively.

Equity Incentive Plans

The following table contains information about the Company's equity incentive plans:


			December 31, 2025		December 31, 2024
Title of Plan	Group Eligible	Type of Award Granted (or to be Granted)	Awards Outstanding	Additional Awards Available for Grant	Awards Outstanding	Additional Awards Available for Grant
Keryx Equity Plans(1)(2)	Employees, directors and consultants	Common stock options and RSUs	148,860	—	163,765	—

Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (2) (3) (the 2014 Plan) (replaces 2008 Plan)	Employees, directors, consultants and advisors	Common stock options, RSUs, SARs and performance awards	8,412,898	—	11,559,708	—
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan, as amended(3) (the 2023 Plan) (replaces 2014 Plan)	Employees, officers, directors, consultants and advisors	Common stock options, SARs, restricted stock, unrestricted stock, RSUs, performance awards, other share-based awards and dividend equivalents	15,913,729	24,723,655	10,390,642	11,340,648

(2) New awards are no longer being granted under these plans.

(4) On June 10, 2025, the 2023 Plan was amended to increase the number of shares of common stock available for issuance thereunder by 18,900,000 shares.

Common Stock Options and Stock Appreciation Rights

During the year ended December 31, 2025, the Company granted 3,634,300 options to employees and 375,200 options to directors under the 2023 Plan. Options and SARs granted by the Company generally vest over periods of between 12 and 48 months, subject, in each case, to the individual’s continued service through the applicable vesting date. Options and SARs generally vest either 100% on the first anniversary of the grant date or in installments of (i) 25% at the one year anniversary and (ii) 12 equal quarterly installments beginning after the one year anniversary of the grant date, subject to the individual’s continuous service with the Company. Options and SARs generally expire ten years after the date of grant.

The Company also maintains an inducement award program with a share pool that is separate from the Company's equity plans under which inducement awards may be granted consistent with Nasdaq Listing Rule 5635(c)(4). During the year ended December 31, 2025, the Company granted 1,454,477 options to purchase shares of the Company’s common stock to new hires as inducements to such employees entering into employment with the Company, of which 1,152,477 options remained outstanding at December 31, 2025.

The Company grants annual service-based stock options to employees and directors and granted SARs to certain executives under the 2023 Plan and previously granted options under the 2014 Plan. In addition, the Company issues common stock options to directors, new hires and occasionally to other employees not in connection with the annual grant process.

Finally, the Company periodically grants performance-based stock options which generally vest in connection with the achievement of specified commercial, regulatory and corporate milestones. The performance-based stock options also generally feature a time-based vesting component. The expense recognized for these awards is based on the grant date fair value of the Company’s common stock multiplied by the number of options granted and recognized over time based on the probability of meeting such commercial, regulatory and corporate milestones.

The combined stock option activity for the year ended December 31, 2025, is as follows:


	Stock Options	Weighted-Average Exercise Price		Weighted-Average Contractual Life (years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2024	16,684,325	$	3.19	7.17 years	$	6,797
Granted	5,464,077	$	2.48
Exercised	(1,205,853)	$	1.40
Expired	(1,165,336)	$	8.67
Canceled and forfeited	(1,624,955)	$	1.99
Outstanding at December 31, 2025	18,152,258	$	2.85	6.97 years	$	3,690
Exercisable at December 31, 2025	9,819,097	$	3.56	5.59 years	$	2,624
Vested and expected to vest at December 31, 2025	18,152,258	$	2.85	6.97 years	$	3,690

The intrinsic value of options exercised during the years ended December 31, 2025 and 2024 was $1.8 million and $0.4 million, respectively. There was immaterial intrinsic value of options exercised during the year ended December 31, 2023, as the value of options exercised in 2023 was immaterial. The fair value of options that vested during the years ended December 31, 2025, 2024 and 2023 was $4.3 million, $3.7 million and $6.4 million, respectively. As of December 31, 2025, there was approximately $11.2 million of unrecognized compensation cost related to common stock options outstanding under the Company’s 2023 Plan or the 2014 Plan or made pursuant to the Company's inducement award program, which is expected to be recognized over a weighted average period of 2.64 years.

Restricted Stock Units

Generally, RSUs granted by the Company vest in one of the following ways: (i) 100% of each RSU grant vests on the first anniversary of the grant date, (ii) one third of each RSU grant vests on the first, second and third anniversaries of the grant date, (iii) 50% of each RSU grant vests on the first anniversary and 25% of each RSU grant vests every six months after the one year anniversary of the grant date, or (iv) one third of each RSU grant vests on the first anniversary of the grant date and the remaining two thirds vests in eight substantially equal quarterly installments beginning after the one year anniversary, subject, in each case, to the individual’s continued service through the applicable vesting date. The grant-date fair value of the RSUs is recognized as expense on a straight-line basis. The Company determines the fair value of the RSUs based on the closing price of the common stock on the date of the grants.

The Company also periodically grants performance-based restricted stock units, or PSUs, to employees under the 2023 Plan and previously granted PSUs under the 2014 Plan. The PSUs granted by the Company generally vest in connection with the achievement of specified commercial, regulatory and corporate milestones. The PSUs also generally feature a time-based

vesting component. The expense recognized for these awards is based on the grant date fair value of the Company’s common stock multiplied by the number of units granted and recognized over time based on the probability of meeting such commercial, regulatory and corporate milestones.

In addition, the Company has granted PSUs to certain employees under the 2023 Plan with a market condition. The PSUs also generally feature a time-based vesting component. The Company uses a Monte Carlo simulation to determine fair value of the award at the grant date. The expense recognized for these awards is based on the calculated fair value multiplied by the number of the target units granted and is amortized over the service period.

RSU and PSU activity is as follows:


	2014 Plan		2023 Plan
	Number of Shares	Weighted Average Grant Date Fair Value	Number of Shares	Weighted Average Grant Date Fair Value
Unvested as of December 31, 2024	1,321,423	$0.95	4,108,367	$1.59
Granted	—	$0.00	4,492,000	$2.31
Vested	(849,701)	$1.06	(1,636,898)	$1.55
Forfeited and canceled	(141,100)	$0.98	(970,862)	$1.89
Unvested as of December 31, 2025	330,622	$0.63	5,992,607	$2.09

The total fair value of RSUs and PSUs that vested during 2025, 2024 and 2023 (measured on the date of vesting) was $3.4 million, $3.2 million and $8.4 million, respectively. As of December 31, 2025, there was approximately $7.7 million of unrecognized compensation cost related to RSUs and PSUs, which is expected to be recognized over a weighted average period of 1.73 years.

Employee Stock Purchase Plan

On June 6, 2019, the Company’s stockholders approved the Amended and Restated 2014 Employee Stock Purchase Plan, or ESPP. Under the ESPP substantially all employees may voluntarily enroll to purchase shares of the Company’s common stock through payroll deductions at a price equal to 85% of the lower of the fair market values of the stock as of the beginning or the end of the six-month offering period. An employee's payroll deductions under the ESPP are limited to 15% of the employee's compensation, and an employee may not purchase more than $25,000 worth of stock during any calendar year. In addition, an employee may not purchase more than 1,500 shares in any six-month offering period. As of December 31, 2025 and 2024, a total of 4,260,647 and 4,448,069 shares of the Company's common stock were available for future issuance under the ESPP, respectively. The Company issued 187,422 shares during the year ended December 31, 2025.

Stock-Based Compensation Expense

The Black-Scholes option pricing model is used to estimate the fair value of the common stock options. The weighted-average assumptions used in calculating the fair values of the rights to acquire stock under the 2023 Plan, the 2014 Plan and inducement awards were as follows:


	Years ended December 31,
Common Stock Options	2025			2024			2023
Risk-free interest rate	3.67%	-	4.38%	3.60%	-	4.66%	3.54%	-	4.81%
Expected volatility	111.61%	-	123.58%	109.98%	-	119.81%	100.97%	-	111.71%
Expected term (years)	5.51	-	6.25	5.51	-	6.25	5.51	-	6.25
Expected dividend yield	—%			—%			—%
Weighted average grant date fair value	$2.14			$1.36			$0.69

The Company has classified stock-based compensation in its consolidated statements of operations and comprehensive loss as follows (in thousands):


	Years ended December 31,
	2025		2024		2023
Cost of goods sold	$	683	$	399	267
Research and development	2,120		1,498		1,964
Selling, general and administrative	8,480		5,840		6,456
Restructuring	—		38		630
Total	$	11,283	$	7,775	$	9,317

Stock-based compensation by type of award was as follows (in thousands):


	Years ended December 31,
	2025		2024		2023
Stock options	$	5,356	$	4,036	$	5,310
Restricted stock units	5,214		3,655		3,637
Performance RSUs	545		—		297
Employee stock purchase plan	168		84		73
Total	$	11,283	$	7,775	$	9,317

Employee Retirement Plan

In 2008, the Company established a retirement plan, or the Plan, authorized by Section 401(k) of the Internal Revenue Code, or IRC. In accordance with the Plan, all employees who have attained the age of 21 are eligible to participate in the Plan as of the first Entry Date, as defined, following their date of employment. Each employee can contribute a percentage of compensation up to a maximum of the statutory limits per year. Company contributions are discretionary and contributions in the amount of approximately $1.9 million, $1.7 million and $1.7 million were made during the years ended December 31, 2025, 2024 and 2023, respectively.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	12 Months Ended
	Dec. 31, 2025 USD ($) financial_institution segment reporting_unit	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of financial institutions maintaining cash \| financial_institution	2
Allowance for credit loss	$ 2,700,000	$ 1,200,000
Estimated useful life (in years)	6 years
Number of operating segments \| segment	1
Impairment losses on long-lived assets	$ 0	$ 0	$ 0
Expected dividend yield	0.00%	0.00%	0.00%
Significant uncertain tax positions	$ 0	$ 0	$ 0
Number of reporting units \| reporting_unit	1
Selling, General, and Administrative Expenses
Summary Of Significant Accounting Policies [Line Items]
Advertising expenses	$ 7,600,000	$ 4,600,000	$ 1,000,000.0

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Revenue and Gross Accounts Receivable By Major Customer (Details) - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
% of Total Gross Revenues \| Fresenius Medical Care Rx
Concentration Risk [Line Items]
Concentration risk percentage	30.00%	48.00%	40.00%
% of Total Gross Revenues \| U.S. Renal Care
Concentration Risk [Line Items]
Concentration risk percentage	29.00%
% of Total Gross Revenues \| DaVita, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	25.00%
% of Total Gross Revenues \| Cencora, Inc.
Concentration Risk [Line Items]
Concentration risk percentage		19.00%	21.00%
% of Total Gross Revenues \| McKesson Corporation
Concentration Risk [Line Items]
Concentration risk percentage		12.00%	11.00%
% of Total Gross Revenues \| Cardinal Health, Inc.
Concentration Risk [Line Items]
Concentration risk percentage			10.00%
% of Gross Accounts Receivable \| Fresenius Medical Care Rx
Concentration Risk [Line Items]
Concentration risk percentage		42.00%
% of Gross Accounts Receivable \| U.S. Renal Care
Concentration Risk [Line Items]
Concentration risk percentage	42.00%
% of Gross Accounts Receivable \| DaVita, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	29.00%	16.00%
% of Gross Accounts Receivable \| Cencora, Inc.
Concentration Risk [Line Items]
Concentration risk percentage		13.00%

LICENSE, COLLABORATION AND OTHER REVENUE - Medice License Agreement - Narrative (Details)		3 Months Ended	12 Months Ended
	May 24, 2023 USD ($) performance_obligation	Jun. 30, 2023 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Disaggregation of Revenue [Line Items]
Other long-term assets			$ 59,681,000	$ 37,377,000
Revenue recognized			0	0	$ 3,738,000
Recognized revenue			236,196,000	160,180,000	194,623,000
Accounts receivable, net			47,031,000	34,368,000
Payables			21,185,000	15,180,000
Medice \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Disaggregation of Revenue [Line Items]
Percentage of net product margin on sales in collaborative arrangement	70.00%
License \| Medice
Disaggregation of Revenue [Line Items]
Upfront payment	$ 10,000,000.0		0
Eligible milestone payments (up to)	$ 100,000,000.0
Tiered royalties, expected timing of satisfaction period (in years)	12 years
Termination of agreement by counterparty, written notice period (in months)	12 months
Termination of agreement eligible by counterparty, period after effective agreement date (in months)	12 months
Number of performance obligations \| performance_obligation	1
Proceeds from customers		$ 8,600,000
Other long-term assets			1,400,000	1,400,000
Contract asset			100,000
Accounts receivable, net			0
Payables			0
License \| Medice \| Minimum
Disaggregation of Revenue [Line Items]
Tiered royalties (as percent)	10.00%
License \| Medice \| Maximum
Disaggregation of Revenue [Line Items]
Tiered royalties (as percent)	30.00%
License \| MEDICE Arzneimittel Pütter GmbH & Co. KG, Side Letter
Disaggregation of Revenue [Line Items]
Recognized revenue					1,000,000.0
License Collaboration And Other Revenue, Royalties \| Medice
Disaggregation of Revenue [Line Items]
Recognized revenue			100,000	0	0
Supply Agreement \| Medice
Disaggregation of Revenue [Line Items]
Upfront payment			0
Recognized revenue			300,000	0	0
Accounts receivable, net			300,000
Payables			0
License, collaboration and other revenue
Disaggregation of Revenue [Line Items]
Recognized revenue			8,864,000	8,000,000	24,322,000
License, collaboration and other revenue \| Medice
Disaggregation of Revenue [Line Items]
Revenue recognized					10,000,000.0
Recognized revenue			$ 411,000	$ 22,000	$ 10,968,000

SUBSEQUENT EVENTS (Details) - Subsequent Event	Jan. 27, 2026 USD ($) ft²
Subsequent Event [Line Items]
Lessee, operating lease, leased square feet \| ft²	43,474
Lessee, operating lease, cost of additional square foot (in dollars per sq foot)	$ 1.00
Total security deposit in connection with lease	$ 800,000
Office Space
Subsequent Event [Line Items]
Lessee, operating lease, leased square feet \| ft²	28,518
Unrecorded unconditional purchase obligation	$ 900,000
Laboratory Space
Subsequent Event [Line Items]
Lessee, operating lease, leased square feet \| ft²	14,956
Unrecorded unconditional purchase obligation	$ 1,000,000.0
Operating lease, increase in rent, percentage	3.00%

CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Operating Activities:
Net loss	$ (5,345)	$ (69,410)	$ (51,925)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,269	1,462	1,585
Amortization of intangible asset	0	36,042	36,042
Bad debt expense	1,479	876	0
Change in fair value of warrant liability	3,099	330	0
Non-cash royalty revenue related to sale of future royalties	(1,768)	(1,895)	(1,977)
Non-cash research and development expense	0	0	782
Non-cash interest expense	21,808	13,069	(2,228)
Non-cash operating lease expense	4,555	4,198	4,219
Non-cash loss on extinguishment of debt	0	294	0
Non-cash write-off on termination of lease	0	0	(825)
Charge for purchase of IPR&D asset	12,807	0	0
Write-down of inventory	2,505	4,208	1,580
Change in excess inventory purchase commitments	0	2,068	1,533
Stock-based compensation expense	11,283	7,775	9,317
Gain on the sale of property and equipment	(172)	0	0
Change in fair value of embedded debt derivative	0	0	(760)
Changes in operating assets and liabilities:
Accounts receivable	(14,142)	4,046	994
Inventory	(23,125)	(28,401)	(2,542)
Prepaid expenses and other current assets	7,579	8,893	11,839
Other long-term assets	(2,622)	622	(1,361)
Accounts payable	3,082	(1,364)	(5,244)
Accrued expense and other current liabilities	48,530	(12,777)	(10,021)
Operating lease liabilities	(5,399)	(4,491)	(4,963)
Deferred revenue	2,681	0	(3,738)
Other long-term liabilities	(112)	(6,204)	(5,691)
Net cash provided by (used in) operating activities	67,992	(40,659)	(23,384)
Investing Activities:
Purchase of equipment	(291)	(33)	0
Proceeds from the sale of property and equipment	172	0	0
Purchase of IPR&D asset, including transaction costs	(7,807)	0	0
Net cash used in investing activities	(7,926)	(33)	0
Financing Activities:
Proceeds from the issuance of debt	10,000	45,000	0
Payments of issuance costs related to BlackRock Credit Agreement	(63)	(1,272)	0
Proceeds from the issuance of common stock, net of issuance costs	66,449	42,495	6,708
Proceeds from the sale of stock under employee stock purchase plan	230	154	85
Proceeds from the exercise of common stock options	1,684	385	1
Repayment of WCF liability	(1,146)	0	0
Repayment of liability related to settlement royalties	(3,765)	0	0
Repayment of term debt	(462)	(37,099)	(32,000)
Net cash provided by (used in) financing activities	72,927	49,663	(25,206)
Increase (decrease) in cash, cash equivalents and restricted cash	132,993	8,971	(48,590)
Cash, cash equivalents and restricted cash at beginning of the period	53,550	44,579	93,169
Cash, cash equivalents and restricted cash at end of the period	186,543	53,550	44,579
Supplemental cash flow information
Issuance of warrants in connection with BlackRock Credit Agreement	2,199	4,846	0
Cashless exercise of warrants in connection with BlackRock Credit Agreement	7,494	0	0
Purchase of IPR&D asset included in accrued expenses and other current liabilities	5,000	0	0
Cash paid for interest	$ 6,080	$ 5,035	$ 6,059

FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2025

Fair Value Disclosures [Abstract]

Schedule of Assets Measured or Disclosed at Fair Value on Recurring Basis

The tables below present certain assets and liabilities measured at fair value categorized by the level of input used in the valuation of each asset and liability (in thousands):


	December 31, 2025
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	172,689	$	—	$	—	$	172,689
Long-term liability:
Warrant liability	$	—	$	2,980	—		$	2,980


	December 31, 2024
	Level 1		Level 2		Level 3	Total
Long-term liability:
Warrant liability	$	—	$	5,176	—	$	5,176

LIABILITY RELATED TO SETTLEMENT ROYALTIES, WORKING CAPITAL FUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES - Schedule of Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Feb. 28, 2021
Other Liabilities Disclosure [Abstract]
Current portion (included in accrued expenses and other current liabilities)	$ 1,664	$ 2,039
Long-term portion	50,608	52,066	$ 44,800
Total liability related to sale of future royalties	$ 52,272	$ 54,105

LIABILITY RELATED TO SETTLEMENT ROYALTIES, WORKING CAPITAL FUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Feb. 28, 2022	Feb. 28, 2021	May 31, 2017	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	May 31, 2028	May 31, 2027	May 31, 2026	Jul. 01, 2025	Jul. 10, 2024	May 03, 2024	Mar. 18, 2022	Feb. 18, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock, issued (in shares)				265,424,818	224,848,992
Annual effective interest rate (as percent)				0.00%
Interest expense				$ (24,179)	$ (18,185)	$ (6,032)
Refund liability to customer, amortization of discount				4,700	3,800	3,100
Refund liability to customer, amortization of deferred gain				3,900	3,600	4,000
Maximum annual royalty payout capacity		$ 13,000
Percentage of royalty payment to be received once maximum annual royalty payout has been paid		85.00%
Maximum aggregate royalty payout capacity		$ 150,000
Liability related to sale of future royalties, net of current portion		$ 44,800		$ 50,608	52,066
Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sale of stock, price per share (in dollars per share)	$ 5.00
Number of shares sold in offering (in shares)	4,000,000
Aggregate net proceeds from offering	$ 20,000
Vifor (International) Ltd.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual effective interest rate (as percent)				22.30%
Interest expense				$ 18,400	9,300
Refund liability to customer, gross													$ 40,000
Vifor (International) Ltd. \| License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock, issued (in shares)			3,571,429
Sale of stock, price per share (in dollars per share)			$ 14.00
Proceeds from common stock sold			$ 50,000
Vifor (International) Ltd. \| License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue, remaining performance obligation, profit share percentage														66.00%
Deferred revenue														$ 25,000
Long-term deferred revenue	$ 13,600		$ 4,700
Transaction price														$ 43,300
Refund liability to customer, interest rate (as percent)													15.00%
Vifor (International) Ltd. \| License \| Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Long-term deferred revenue				18,300
CSL Vifor
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered royalty payments as a percentage of net sales											$ 450,000
Refund liability to customer, interest rate (as percent)												15.00%
Royalty payments										$ 40,000
CSL Vifor \| Forecast
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalty true-up payments							$ 40,000	$ 20,000	$ 10,000
CSL Vifor \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered royalty payments, percentage												8.00%
CSL Vifor \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered royalty payments as a percentage of net sales											$ 450,000
Tiered royalty payments, percentage												14.00%
Vifor International Limited, First Investment \| License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Long-term deferred revenue				4,700
Vifor International Limited, Second Investment \| License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Long-term deferred revenue				13,600
HealthCare Royalty Partners IV, L.P.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payments for royalties				$ 1,800	$ 2,000	$ 2,000

CAPITAL STOCK	12 Months Ended
CAPITAL STOCK	Dec. 31, 2025
Equity [Abstract]
CAPITAL STOCK	CAPITAL STOCK Authorized and Outstanding Capital Stock As of December 31, 2025, the authorized capital stock of the Company included 350,000,000 shares of common stock, $0.00001 par value per share, of which 265,424,818 and 224,848,992 shares were issued and outstanding at December 31, 2025 and 2024, respectively; and 25,000,000 shares of undesignated preferred stock, $0.00001 par value per share, of which no shares were issued and outstanding at December 31, 2025 and 2024. At-the-Market Facility On April 7, 2022, the Company entered into an at-the-market, or the ATM, sales agreement, or the Original Sales Agreement, with Jefferies LLC, or Jefferies, as the Company's sales agent, under which the Company could offer and sell from time to time up to $26.0 million of shares of its common stock at current market prices. During the year ended December 31, 2023, the Company sold 6,189,974 shares of common stock under this program for gross proceeds of $6.8 million ($6.7 million, net of offering expenses). During the year ended December 31, 2024, the Company sold 13,261,311 shares of its common stock under this program with gross proceeds of $19.2 million, ($18.7 million, net of offering expenses). On September 3, 2024, in connection with the filing of a new shelf registration statement on Form S-3, the Company filed a prospectus related to the Company's amended and restated sales agreement (which amended and restated the Original Sales Agreement), with Jefferies, as the Company’s sales agent, pursuant to which the Company is able to offer and sell up to $75.0 million of its common stock at current market prices from time to time. Since September 12, 2024 (the date the Company’s shelf registration statement on Form S-3 went effective) through December 31, 2024, the Company sold 14,271,631 shares of its common stock under this program with gross proceeds of $24.3 million ($23.8 million, net of offering expenses). During the year ended December 31, 2025, the Company sold 9,437,364 shares of its common stock under this program with gross proceeds of $18.7 million ($18.4 million, net of offering expenses). Public Offering On March 19, 2025, the Company entered into an underwriting agreement, or the Underwriting Agreement, with Leerink Partners LLC and Piper Sandler & Co., as representatives of the several underwriters named therein, collectively, the Underwriters, relating to an underwritten public offering, or the Offering, of 25,000,000 shares, or the Shares, of the Company's common stock. The offering price was $2.00 per share, and the Underwriters agreed to purchase the Shares from the Company pursuant to the Underwriting Agreement at a price of $1.88 per share. Under the terms of the Underwriting Agreement, the Company granted the Underwriters a 30-day option to purchase up to 3,750,000 additional shares of common stock, or the Additional Shares, at the public offering price per share, and the Underwriters partially exercised their option and purchased 850,000 Additional Shares on April 22, 2025. Net proceeds from the Offering were $46.5 million, after deducting underwriting discounts and commissions and offering expenses and net proceeds from the Offering of the Additional Shares were $1.6 million, after deducting underwriting discounts and commissions and offering expenses. Unregistered Common Stock In connection with the Vifor License Agreement, CSL Vifor owns 7,571,429 shares of common stock that are unregistered under the Securities Act. See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for more information. Warrants to Purchase Common Stock In connection with the BlackRock Credit Agreement, described in more detail in Note 7, Indebtedness, the Company issued a warrant to purchase 3,076,923 shares of the Company’s common stock, at an exercise price per share of $1.30, and upon the borrowing of Tranche C in February 2025, the Company issued additional warrants to purchase 1,153,846 shares of the Company’s common stock at an exercise price per share of $1.30. Each warrant is exercisable for eight years from the date of issuance. The warrants and the common stock issuable upon the exercise of such warrants were not registered under the Securities Act. Accordingly, the holder thereof may only sell common stock issued upon exercise of such warrants pursuant to an effective registration statement under the Securities Act covering the resale of those shares, an exemption under Rule 144 under the Securities Act or another applicable exemption under the Securities Act. On July 21, 2025, the Warrant Holder exercised its option to purchase 2,115,384 shares of the Company's common stock under the Initial Warrant on a cashless basis at an exercise price per share of $1.30. The cashless exercise allowed the Warrant Holder to convert the warrants into shares of the Company's common stock without the need for a cash payment. Instead of paying cash upon exercise, the Warrant Holder received a reduced number of shares based on a predetermined formula. On July 23, 2025, as a result of the cashless exercise, the Company issued 1,408,588 shares of common stock to the Warrant Holder under the Initial Warrant.

- Definition

The entire disclosure for equity.

+ References

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+ Details

INDEBTEDNESS - Schedule of Future Principal Payments on the Term Loans (Details) $ in Thousands	Dec. 31, 2025 USD ($)
Debt Disclosure [Abstract]
2026	$ 0
2027	50,558
2028	1,881
Total before unamortized discount and issuance costs	52,439
Less: unamortized discount and issuance costs	(4,189)
Total term loans	$ 48,250

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References + Details

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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+ Details

LICENSE, COLLABORATION AND OTHER REVENUE (Tables)

12 Months Ended

Dec. 31, 2025

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Revenues Recognized from License, Collaboration and Other Significant Agreements

The Company recognized the following revenues from its license, collaboration and other revenue agreements (in thousands):


		Years Ended December 31,
Entity	Description	2025		2024		2023
Medice	License and Product Supply of Vafseo in EU	$	411	$	22	$	10,968
TPC, formerly known as Mitsubishi Tanabe Pharma	License and Product Supply of Vafseo in Japan	2,794		2,612		5,735
JT and Torii	License and royalties related to the sale of Riona in Japan	5,659		5,366		5,394
Otsuka	Terminated U.S. and International Agreements	—		—		2,225
Total License, Collaboration and Other Revenue		$	8,864	$	8,000	$	24,322

Schedule of Changes in Contract Assets and Liabilities

The following table presents changes in the Company’s contract assets and liabilities related to the Company's sales to its AG Distributor (in thousands):


	Year Ended December 31, 2025
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable	$	—	$	12,006	$	(11,812)	$	194
Contract liabilities:
Deferred revenue	$	—	$	10,675	$	(7,994)	$	2,681

The following table presents changes in the Company’s contract assets and liabilities related to license, collaboration and other revenue agreements (in thousands):


	Year Ended December 31, 2025
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable(1)	$	2,010	$	8,894	$	(8,513)	$	2,391
Contract liability:
Deferred revenue	$	—	$	—	$	—	$	—

	Year Ended December 31, 2024
	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Contract assets:
Accounts receivable(1)	$	3,333	$	8,562	$	(9,885)	$	2,010
Contract liabilities:
Deferred revenue (long-term)(2)	$	43,296	$	—	$	(43,296)	$	—

(1)Excludes accounts receivable from product sales of Auryxia and Vafseo which are included in the accompanying consolidated balance sheets as of December 31, 2025 and 2024.

(2)See Note 8, Liability Related to Settlement Royalties, Working Capital Fund Liability and Liability Related to Sale of Future Royalties, for further information.

Schedule of Revenue Recognized Resulting from Changes in Contract Assets and Contract Liabilities


	Years Ended December 31,
Revenue Recognized in the Period from:	2025		2024		2023
Deferred revenue - beginning of the period	$	—	$	—	$	3,738

LEASES - Narrative (Details) $ in Thousands	1 Months Ended	12 Months Ended
LEASES - Narrative (Details) $ in Thousands	May 31, 2023 USD ($)	Dec. 31, 2025 USD ($) ft² extension_option	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, remaining lease term (in years)		8 months 12 days
Operating lease, cost		$ 5,000	$ 5,000	$ 5,700
Operating lease, payments		5,800	5,700	5,900
Loss on termination of lease		$ 0	0	524
Minimum
Lessee, Lease, Description [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term		6.65%
Maximum
Lessee, Lease, Description [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term		6.94%
Cambridge
Lessee, Lease, Description [Line Items]
Area of property leased (in square feet) \| ft²		65,167
Cambridge \| Letter of Credit
Lessee, Lease, Description [Line Items]
Total security deposit in connection with lease		$ 1,700	1,700
Cambridge \| Office And Storage Space
Lessee, Lease, Description [Line Items]
Leased area subject to expiration \| ft²		59,216
Operating lease extensions (in extension options) \| extension_option		1
Lease extension period		5 years
Cambridge \| Laboratory Space
Lessee, Lease, Description [Line Items]
Leased area subject to expiration \| ft²		5,951
Operating lease extensions (in extension options) \| extension_option		1
Lease extension period		2 years
Boston \| Office Space
Lessee, Lease, Description [Line Items]
Area of property leased (in square feet) \| ft²		27,924
Payments to transfer rights and obligations of operating lease	$ 1,300
Boston \| Office Space \| Keryx Biopharmaceuticals, Inc.
Lessee, Lease, Description [Line Items]
Sublease rent payments received		$ 0	$ 0	$ 300

PRODUCT REVENUE AND PROVISIONS FOR VARIABLE CONSIDERATION - Schedule of Product Revenue Allowance and Provision Categories (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 23,604	$ 31,514	$ 38,434
Provisions related to sales in current year	85,704	59,001	96,967
Adjustments related to prior year sales	(1,419)	(2,690)	(162)
Credits/payments made	(30,796)	(64,221)	(103,725)
Ending balance	77,093	23,604	31,514
Chargebacks and Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	1,436	1,607	1,259
Provisions related to sales in current year	4,051	9,225	11,138
Adjustments related to prior year sales	69	(94)	(304)
Credits/payments made	(4,403)	(9,302)	(10,486)
Ending balance	1,153	1,436	1,607
Rebates, Fees and other Deductions
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	15,726	22,991	26,252
Provisions related to sales in current year	81,019	44,914	79,648
Adjustments related to prior year sales	143	(2,056)	(1,506)
Credits/payments made	(24,299)	(50,123)	(81,403)
Ending balance	72,589	15,726	22,991
Returns
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	6,442	6,916	10,923
Provisions related to sales in current year	634	4,862	6,181
Adjustments related to prior year sales	(1,631)	(540)	1,648
Credits/payments made	(2,094)	(4,796)	(11,836)
Ending balance	$ 3,351	$ 6,442	$ 6,916

LEASES (Tables)

12 Months Ended

Dec. 31, 2025

Leases [Abstract]

Schedule of Future Commitments under Non-Cancelable Leases

Future commitments under the non-cancelable Cambridge Lease are as follows (in thousands):


	Operating Lease
2026	$	3,613


Less: present value adjustment	(65)
Current operating lease liabilities	$	3,548

LICENSE, COLLABORATION AND OTHER REVENUE - Schedule of Changes In Contract Assets and Liabilities related to License, Collaboration and Other Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Accounts receivable
Contract assets:
Additions	$ 8,894	$ 8,562
Deductions	(8,513)	(9,885)
Deferred revenue
Contract liability:
Additions	0	0
Deductions	0	(43,296)
Accounts receivable
Contract assets:
Balance at Beginning of Period	2,010	3,333
Balance at End of Period	2,391	2,010
Deferred revenue
Contract liability:
Balance at Beginning of Period	0	43,296
Balance at End of Period	$ 0	$ 0

LICENSE, COLLABORATION AND OTHER REVENUE - U.S. Collaboration and License Agreement with Otsuka Pharmaceutical Co. Ltd. - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 236,196	$ 160,180	$ 194,623
License, collaboration and other revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	8,864	8,000	24,322
Otsuka \| License, collaboration and other revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 0	$ 0	$ 2,225

- Definition

+ References

+ Details

ADDITIONAL BALANCE SHEET DETAIL - Schedule of Prepaids and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Payables and Accruals [Abstract]
Prepaid manufacturing	$ 0	$ 4,029
Restricted cash	1,699	0
Other	3,771	7,321
Prepaid expenses and other current assets	$ 5,470	$ 11,350

INDEBTEDNESS (Tables)

12 Months Ended

Dec. 31, 2025

Debt Disclosure [Abstract]

Schedule of Future Principal Payments on the Term Loans

As of December 31, 2025, future principal payments under the BlackRock Credit Agreement are as follows (in thousands):


Years ended December 31,	Amounts


2026	—
2027	50,558
2028	1,881
Total before unamortized discount and issuance costs	52,439
Less: unamortized discount and issuance costs	(4,189)
Total term loans	$	48,250

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Reconciliations (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 184,844	$ 51,870	$ 42,925
Restricted cash	1,699	1,680	1,654
Total cash, cash equivalents and restricted cash	$ 186,543	$ 53,550	$ 44,579	$ 93,169