Akebia Therapeutics (AKBA) 10-Q 8 Aug 24 2024 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2024	Aug. 05, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2024
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		210,288,210
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001517022

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 39,499	$ 42,925
Inventories	23,872	15,691
Accounts receivable, net	29,765	39,290
Prepaid expenses and other current assets	18,961	20,243
Total current assets	112,097	118,149
Property and equipment, net	2,895	3,629
Operating right-of-use assets	10,360	12,416
Intangible asset, net	18,021	36,042
Goodwill	59,044	59,044
Other long-term assets	17,779	12,423
Total assets	220,196	241,703
Current liabilities:
Accounts payable	10,107	14,635
Accrued expenses and other current liabilities	53,897	67,735
Current portion of deferred revenue	43,296	0
Current portion of long-term debt	0	17,500
Total current liabilities	107,300	99,870
Deferred revenue, net of current portion	0	43,296
Long-term operating lease liabilities	6,299	8,947
Long-term debt, net	38,031	17,183
Liability related to sale of future royalties, net of current portion	53,101	54,013
Refund liability to customer	40,018	40,093
Warrant liability	2,644	0
Other long-term liabilities	6,557	8,885
Total liabilities	253,950	272,287
Commitments and contingencies (Note 10)
Stockholders' deficit:
Preferred stock $0.00001 par value, 25,000,000 shares authorized; no shares issued and    outstanding at June 30, 2024 and December 31, 2023	0	0
Common stock $0.00001 par value; 350,000,000 shares authorized at June 30, 2024 and December 31, 2023; 209,929,145 and 194,582,539 shares issued and outstanding at June 30, 2024 and December 31, 2023, respectively	2	2
Additional paid-in capital	1,601,755	1,578,358
Accumulated other comprehensive income	6	6
Accumulated deficit	(1,635,517)	(1,608,950)
Total stockholders' deficit	(33,754)	(30,584)
Total liabilities and stockholders' deficit	$ 220,196	$ 241,703

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2024	Dec. 31, 2023	Jun. 04, 2020
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	175,000,000
Common stock, issued (in shares)	209,929,145	194,582,539
Common stock, outstanding (in shares)	209,929,145	194,582,539

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues
Total revenues	$ 43,648	$ 56,376	$ 76,255	$ 96,381
Cost of goods sold
Cost of product and other revenue	8,036	8,273	10,630	19,452
Amortization of intangible asset	9,011	9,011	18,021	18,021
Total cost of goods sold	17,047	17,284	28,651	37,473
Operating expenses:
Research and development	7,647	20,197	17,379	39,883
Selling, general and administrative	26,917	27,036	52,354	52,090
License	762	949	1,473	1,517
Restructuring	0	(94)	58	12
Total operating expenses	35,326	48,088	71,264	93,502
Loss from operations	(8,725)	(8,996)	(23,660)	(34,594)
Other income (expense)
Interest expense	(2,149)	(1,642)	(4,647)	(3,204)
Other (expense) income	(39)	(10)	56	272
Change in fair value of warrant liability	2,331	0	2,201	0
Loss on extinguishment of debt	0	0	(517)	0
Loss on termination of lease	0	(524)	0	(524)
Net loss before income taxes	(8,582)	(11,172)	(26,567)	(38,050)
Net (loss) income, basic	(8,582)	(11,172)	(26,567)	(38,050)
Net (loss) income, diluted	(8,582)	(11,172)	(26,567)	(38,050)
Comprehensive loss	$ (8,582)	$ (11,172)	$ (26,567)	$ (38,050)
Net loss per share:
Basic (in dollars per share)	$ (0.04)	$ (0.06)	$ (0.13)	$ (0.20)
Diluted (in dollars per share)	$ (0.04)	$ (0.06)	$ (0.13)	$ (0.20)
Weighted average common shares outstanding:
Basic (in shares)	209,705,397	186,817,431	207,330,274	185,798,865
Diluted (in shares)	209,705,397	186,817,431	207,330,274	185,798,865
Product revenue, net
Revenues
Total revenues	$ 41,209	$ 42,244	$ 72,218	$ 76,950
License, collaboration and other revenue
Revenues
Total revenues	$ 2,439	$ 14,132	$ 4,037	$ 19,431

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED 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]
Proceeds from sale of stock under employee stock purchase plan (in shares)		103,500
Proceeds from sale of stock under    employee stock purchase plan	34		34
Stock-based compensation expense	2,489		2,489
Restricted stock unit vesting (in shares)		1,596,732
Net income (loss)	(26,876)				(26,876)
Ending balance (in shares) at Mar. 31, 2023		185,835,946
Ending balance at Mar. 31, 2023	(19,123)	$ 2	1,564,770	6	(1,583,901)
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]
Net income (loss)	(38,050)
Ending balance (in shares) at Jun. 30, 2023		188,128,869
Ending balance at Jun. 30, 2023	(26,805)	$ 2	1,568,260	6	(1,595,073)
Beginning balance (in shares) at Mar. 31, 2023		185,835,946
Beginning balance at Mar. 31, 2023	(19,123)	$ 2	1,564,770	6	(1,583,901)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	3,490		3,490
Restricted stock unit vesting (in shares)		2,292,923
Net income (loss)	(11,172)				(11,172)
Ending balance (in shares) at Jun. 30, 2023		188,128,869
Ending balance at Jun. 30, 2023	$ (26,805)	$ 2	1,568,260	6	(1,595,073)
Beginning balance (in shares) at Dec. 31, 2023	194,582,539	194,582,539
Beginning 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)		13,261,311
Issuance of common stock, net of    issuance costs	18,740		18,740
Proceeds from sale of stock under employee stock purchase plan (in shares)		92,321
Proceeds from sale of stock under    employee stock purchase plan	70		70
Exercise of options (in shares)		280,260
Exercise of options	141		141
Stock-based compensation expense	2,360		2,360
Restricted stock unit vesting (in shares)		1,237,718
Net income (loss)	(17,985)				(17,985)
Ending balance (in shares) at Mar. 31, 2024		209,454,149
Ending balance at Mar. 31, 2024	$ (27,258)	$ 2	1,599,669	6	(1,626,935)
Beginning balance (in shares) at Dec. 31, 2023	194,582,539	194,582,539
Beginning balance at Dec. 31, 2023	$ (30,584)	$ 2	1,578,358	6	(1,608,950)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (in shares)	304,152
Net income (loss)	$ (26,567)
Ending balance (in shares) at Jun. 30, 2024	209,929,145	209,929,145
Ending balance at Jun. 30, 2024	$ (33,754)	$ 2	1,601,755	6	(1,635,517)
Beginning balance (in shares) at Mar. 31, 2024		209,454,149
Beginning balance at Mar. 31, 2024	(27,258)	$ 2	1,599,669	6	(1,626,935)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of options (in shares)		23,892
Exercise of options	14		14
Stock-based compensation expense	2,072		2,072
Restricted stock unit vesting (in shares)		451,104
Net income (loss)	$ (8,582)				(8,582)
Ending balance (in shares) at Jun. 30, 2024	209,929,145	209,929,145
Ending balance at Jun. 30, 2024	$ (33,754)	$ 2	$ 1,601,755	$ 6	$ (1,635,517)

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ DEFICIT (Parenthetical) - $ / shares	Jun. 30, 2024	Dec. 31, 2023
Statement of Stockholders' Equity [Abstract]
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001

UNAUDITED CONDENSED CONSOLIDA_6

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Operating Activities:
Net loss	$ (26,567)	$ (38,050)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	764	795
Amortization of intangible asset	18,021	18,021
Change in fair value of warrant liability	(2,201)	0
Non-cash royalty revenue related to sale of future royalties	(865)	(936)
Non-cash research and development expense	0	782
Non-cash interest expense	229	983
Non-cash operating lease expense	2,056	(955)
Non-cash write-off from termination of lease	0	(825)
Non-cash loss on extinguishment of debt	294	0
Write-down of inventory	1,061	612
Change in excess inventory purchase commitments	2,068	0
Stock-based compensation expense	4,432	5,979
Changes in operating assets and liabilities:
Accounts receivable	9,525	20,712
Inventory	(19,360)	10,828
Prepaid expenses and other current assets	1,282	7,684
Other long-term assets	452	(5,876)
Accounts payable	(726)	(12,058)
Accrued expense and other current liabilities	(14,526)	(19,382)
Operating lease liabilities	(1,959)	1,034
Deferred revenue	0	(3,738)
Other long-term liabilities	(3,478)	481
Net cash used in operating activities	(29,498)	(13,909)
Investing Activities:
Purchases of equipment	(29)	0
Net cash used in investing activities	(29)	0
Financing Activities:
Proceeds from the issuance of debt	45,000	0
Payments of issuance costs related to BlackRock Credit Agreement	(750)	0
Proceeds from issuance of common stock, net of issuance costs	18,740	0
Proceeds from issuance of stock under employee stock purchase plan	70	34
Proceeds from the exercise of stock options	155	0
Repayment of term debt	(37,100)	(24,000)
Net cash provided by (used in) financing activities	26,115	(23,966)
Decrease in cash, cash equivalents and restricted cash	(3,412)	(37,875)
Cash, cash equivalents and restricted cash — beginning of period	44,579	93,169
Cash, cash equivalents and restricted cash — end of period	41,167	55,294
Non-cash financing activities
Issuance of warrants in connection with BlackRock Credit Agreement	4,846	0
Unpaid issuance costs related to BlackRock Credit Agreement	$ 522	$ 0

NATURE OF BUSINESS

NATURE OF BUSINESS	6 Months Ended
	Jun. 30, 2024
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 committed to addressing patients' unmet needs. The Company's purpose is to better the life of each person impacted by kidney disease. 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. on March 27, 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. The Company is launching Vafseo in the U.S. Auryxia ® (ferric citrate) is marketed 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 will lose 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 providing general and administrative support for these operations. The Company began recording revenue from the U.S. sales of Auryxia and revenue from sublicensing rights to Auryxia in Japan from the Company’s Japanese partners, Japan Tobacco, Inc. and its subsidiary Torii Pharmaceutical Co., Ltd., collectively, JT and Torii , in 2018. In addition, the Company continues to explore additional development opportunities to expand its pipeline and portfolio of novel therapeutics. As of June 30, 2024, the Company had cash and cash equivalents of approximately $39.5 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 for at least twelve months from the filing of this Quarterly Report on Form 10-Q, or Form 10-Q . However, if the Company’s operating performance deteriorates significantly from the levels expected in the Company’s operating plan, 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. If the Company believes its resources are insufficient to satisfy its liquidity requirements, it 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.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES The Company's significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2023, and notes thereto, which are included in the Company's Annual Report on Form 10-K, that was filed with the Securities and Exchange Commission, or SEC , on March 14, 2024, or the 2023 Form 10-K . Since the date of those financial statements, there have been no material changes to the Company's significant accounting policies. In the opinion of management, all adjustments, consisting of normal recurring accruals and revisions of estimates, considered necessary for a fair presentation of the unaudited condensed consolidated financial statements have been included. Interim results for the three and six months ended June 30, 2024 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2024 or any other future period. The Company has experienced seasonality from quarter to quarter. In general, the first quarter usually has lower revenues than the preceding fourth quarter, the second and third quarters have higher revenues than the first quarter, and the fourth quarter revenues are the highest in the year. Basis of Presentation and Principles of Consolidation The accompanying unaudited condensed 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 . The accompanying unaudited condensed 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. Certain monetary amounts, percentages, and other figures included elsewhere in these unaudited condensed 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 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 unaudited condensed consolidated financial statements include, but are not limited to: accrued expenses, other long-term liabilities, product revenues, including various rebates, returns and reserves 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, intangible asset 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 June 30, 2024, cash and cash equivalents primarily included cash on hand. 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 “other long-term assets” in the consolidated balance sheets. The following table reconciles cash, cash equivalents and restricted cash reported within the Company's consolidated balance sheets to the total amounts showing in the consolidated statements of cash flows: (in thousands) June 30, 2024 December 31, 2023 Cash and cash equivalents $ 39,499 $ 42,925 Restricted cash included in other long-term assets 1,668 1,654 Total cash, cash equivalents and restricted cash $ 41,167 $ 44,579 Concentration of 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. The Company's allowance for credit losses was $0.2 million and $1.0 million as of June 30, 2024 and December 31, 2023, respectively. For the six months ended June 30, 2024, net recoveries were $0.2 million, inclusive of an incremental allowance for credit losses of $0.2 million for the three months ended June 30, 2024. Write-offs were $0.6 million for the three and six months ended June 30, 2023. 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 product 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 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 active pharmaceutical ingredients and formulated drugs or distribution of finished product to the market. Recent Accounting Pronouncements Not Yet Adopted In November 2023, the FASB issued ASU 2023-07, Improvements to Reportable Segment Disclosures . ASU 2023-07 requires disclosure of significant segment expenses that are regularly provided to the chief operating decision maker, or CODM, and included within the segment measure of profit or loss, an amount and description of its composition for other segment items to reconcile to segment profit or loss, and the title and position of the entity’s CODM. ASU 2023-07 will be applied retrospectively and is effective for annual reporting periods in fiscal years beginning after December 15, 2023, and interim reporting periods in fiscal years beginning after December 31, 2024. The Company is currently reviewing the impact that the adoption of ASU 2023-07 may have on its consolidated financial statements and disclosure. 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 will be effective for the annual reporting periods in fiscal years beginning after December 15, 2024. The Company is currently evaluating ASU 2023-09 and does not expect it to have a material effect on the Company’s consolidated financial statements.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS	FAIR VALUE OF FINANCIAL INSTRUMENTS 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): June 30, 2024 Level 1 Level 2 Level 3 Total Fair Value Long-term liability: Warrant liability $ — $ 2,644 $ — $ 2,644 December 31, 2023 Level 1 Level 2 Level 3 Total Fair Value Cash equivalents: Money market funds $ 1,504 $ — $ — $ 1,504 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 June 30, 2024, the Company did not have any money market funds included in cash equivalents. Warrant liability –

INVENTORIES AND PREPAID MANUFAC

INVENTORIES AND PREPAID MANUFACTURING	6 Months Ended
	Jun. 30, 2024
Inventory Disclosure [Abstract]
INVENTORIES AND PREPAID MANUFACTURING	INVENTORIES AND PREPAID MANUFACTURING Inventories consists of the following (in thousands): June 30, 2024 December 31, 2023 Inventories, current: Work-in-process $ 9,547 $ 4,297 Finished goods 14,325 11,394 Inventories, current $ 23,872 $ 15,691 Long-term inventories included in other long-term assets: Raw materials 403 1,143 Work-in-process 14,795 8,260 Inventories, long-term 15,198 9,403 Total inventories $ 39,070 $ 25,094 As of June 30, 2024 and December 31, 2023, inventory consisted primarily of inventory related to the Company's commercial product, Auryxia. As of June 30, 2024 and December 31, 2023, the Company had no prepaid manufacturing costs and $0.5 million of prepaid manufacturing costs for Auryxia drug substance, respectively. Inventory written down for Auryxia as a result of excess, obsolescence, scrap or other reasons charged to cost of product and other revenue in the unaudited condensed consolidated statement of operations and comprehensive loss totaled approximately $0.5 million and $1.1 million during the three and six months ended June 30, 2024, respectively, and $0.3 million and $0.6 million during the three and six months ended June 30, 2023, respectively. For the three and six months ended June 30, 2024, the Company realized lower cost of product and other revenue of $4.9 million and $8.6 million, respectively, due to the Company's ability to commercially sell inventory previously written down to zero, its then net realizable value. Pre-Launch Inventory The Company records advance payments for Vafseo active pharmaceutical ingredient, or API , or drug substance (raw materials) it expects to use for the U.S. launch and the EEA, the UK, Switzerland and Australia, or the Medice Territory , as prepaid manufacturing costs. Upon the quality release of the Vafseo batches and transfer of title to the Company from the contract manufacturing organization, or CMO , the cost of the pre-launch inventory prior to regulatory approval, including the manufacturing costs, was expensed to R&D. As of June 30, 2024 and December 31, 2023, the Company had $11.6 million and $14.0 million, respectively, of prepaid manufacturing costs for Vafseo drug substance expected to be used in the U.S. launch of Vafseo included in prepaid expenses and other current assets on the unaudited condensed consolidated balance sheets. See Note 6, Additional Balance Sheet Detail

INTANGIBLE ASSET AND GOODWILL

INTANGIBLE ASSET AND GOODWILL	6 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSET AND GOODWILL	INTANGIBLE ASSET AND GOODWILL Intangible Asset Intangible asset, net of accumulated amortization, prior impairments and adjustments as of June 30, 2024 and December 31, 2023 consisted of the following (in thousands): June 30, 2024 December 31, 2023 Intangible asset: Gross Carrying Accumulated Amortization Net Book Value Net Book Value Estimated Useful Life Developed product rights for Auryxia $ 214,705 $ (196,684) $ 18,021 $ 36,042 6 years The Company recorded $9.0 million in amortization expense for each of the three months ended June 30, 2024 and 2023, and $18.0 million for each of the six months ended June 30, 2024 and 2023 related to the developed product rights for Auryxia. Goodwill

ADDITIONAL BALANCE SHEET DETAIL

ADDITIONAL BALANCE SHEET DETAIL	6 Months Ended
	Jun. 30, 2024
Payables and Accruals [Abstract]
ADDITIONAL BALANCE SHEET DETAIL	ADDITIONAL BALANCE SHEET DETAIL Prepaid expenses and other current assets are as follows (in thousands): Description June 30, 2024 December 31, 2023 Prepaid manufacturing $ 11,632 $ 14,489 Other 7,329 5,754 Total prepaid expenses and other current assets $ 18,961 $ 20,243 See Note 4, Inventories and Prepaid Manufacturing , for further information on prepaid manufacturing expenses. Other long-term assets are as follows (in thousands): Description June 30, 2024 December 31, 2023 Long-term inventories $ 15,198 $ 9,403 Restricted cash 1,668 1,654 Other 913 1,366 Total other long-term assets $ 17,779 $ 12,423 See Note 4, Inventories and Prepaid Manufacturing , for further information on long-term inventories. Cloud Computing Implementation Costs The Company incurs costs to implement cloud computing arrangements that are hosted by a third-party vendor. In accordance with ASC 350-40, Goodwill and Other, Internal-Use Software , for cloud computing arrangements that meet the definition of a service contract, the Company capitalizes qualifying implementation costs incurred during the application development stage as a component of other assets. Capitalization of these costs concludes once the project is substantially complete and the software is ready for the Company's intended use. Once available for its intended use, the capitalized costs are amortized on a straight-line basis over the term of the associated hosting arrangement including periods covered by an option to extend, and are included in selling, general and administrative expenses in the consolidated statements of operations and comprehensive loss. Costs related to data conversion, overhead, general and administrative activities, and training are expensed as incurred. Post-configuration training and maintenance costs will be expensed as incurred. Other long-term assets as of June 30, 2024 included approximately $0.9 million of capitalized implementation costs. There were no implementation costs capitalized as of December 31, 2023. Amortization expense for the capitalized implementation costs was immaterial for the three and six months ended June 30, 2024. There was no amortization expense for the three and six months ended June 30, 2023. Accrued expenses and other current liabilities consists of the following (in thousands): Description June 30, 2024 December 31, 2023 Product revenue allowances $ 14,733 $ 22,940 Product return reserves, current portion 4,337 5,420 Clinical trial costs 227 328 Compensation and related benefits 6,364 8,216 Operating lease liabilities, current portion 5,179 4,491 Royalties due to Panion & BF Biotech, Inc. 3,260 3,989 Professional fees 1,485 1,909 Accrued manufacturing costs 1,165 5,555 Restructuring costs, current portion 723 737 BioVectra, Inc. termination fees, current portion 10,000 7,500 Liability related to sale of future royalties, current portion 2,013 2,048 Other 4,411 4,602 Total accrued expenses and other current liabilities $ 53,897 $ 67,735

INDEBTEDNESS

INDEBTEDNESS	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
INDEBTEDNESS	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 is available in three tranches (i) Tranche A — $37.0 million was funded on the Closing Date and used to repay the Pharmakon Term Loans; (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 is available in a single draw through December 31, 2024, collectively the Term Loans . Tranche C is 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. On the Closing Date, the Company drew $34.5 million on Tranche A, after deducting debt issuance costs, fees and expenses. On the Tranche B Closing Date, the Company drew $7.5 million, after deducting debt issuance costs, 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) term Secured Overnight Financing Rate 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 June 30, 2024, the Company's interest rate was 12.09%. The Company recognized interest expense related to the BlackRock Credit Agreement of $1.6 million and $3.8 million during the three and six months ended June 30, 2024, 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 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. If prepayment is made during the first year, the Company also is required to pay the amount of otherwise due interest payments for the twelve-month period following prepayment. As of June 30, 2024, future principal payments under the BlackRock Credit Agreement are as follows (in thousands): Principal Payments 2024 $ — 2025 — 2026 — 2027 41,363 2028 1,589 Total before unamortized discount and issuance costs 42,952 Less: unamortized discount and issuance costs (4,921) Total term loans $ 38,031 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 Vifor Termination Agreement, the Company and Kreos entered into a First Amendment to the BlackRock Credit Agreement, or the BlackRock Credit Amendment , which amends certain provisions of the BlackRock Credit Agreement. See Note 16, Subsequent Events , for further information on the BlackRock Credit Amendment. 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 , and upon borrowing of Tranche C, the Company would become obligated to issue to the Warrant Holder 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 shall be exercisable for eight years from the date of issuance. The Initial Warrant is liability classified under ASC 815, Derivatives and Hedging , as it could potentially require net cash settlement outside of the Company’s control. The Initial Warrant is measured at fair value each period with changes in fair value presented within the unaudited condensed consolidated statements of operations. The fair value of the warrant liability was $2.6 million as of June 30, 2024. 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 the sale of future royalties which is accounted for as a debt arrangement. See Note 8, Deferred Revenue, Refund Liability and Liability Related to Sale of Future Royalties , for further information. The Company has a refund liability with Vifor (International) Ltd. (now a part of CSL Limited), or CSL Vifor , which is also accounted for as a debt arrangement. See Note 8, Deferred Revenue, Refund Liability and Liability Related to Sale of Future Royalties , for further information. Pharmakon Term Loans (Extinguished January 29, 2024) On November 11, 2019, the Company, with Keryx as guarantor, entered into a loan agreement, or Pharmakon Loan Agreement , with BioPharma Credit PLC as collateral agent and a lender, or Collateral Agent, and BioPharma Credit Investments V (Master) LP as a lender, and a Guaranty and Security Agreement with the Collateral Agent. BioPharma Credit PLC subsequently transferred its interest in the loans, solely in its capacity as a lender, to its affiliate, BPCR Limited Partnership. The Collateral Agent and the lenders are collectively referred to as Pharmakon . The Pharmakon Loan Agreement, as amended, consisted of a secured term loan facility in an aggregate amount of up to $100.0 million, or Pharmakon Term Loans , which was made available under two tranches: (i) Pharmakon Tranche A - $80.0 million and (ii) Pharmakon Tranche B - $20.0 million. On November 25, 2019, the Company drew $77.3 million on Pharmakon Tranche A, net of fees and expenses of $2.7 million. On December 10, 2020, the Company drew $20.0 million on Pharmakon Tranche B, net of immaterial lender expenses and issuance costs. 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 six months ended June 30, 2024, the Company recorded a debt extinguishment loss of $0.5 million. The Pharmakon Term Loans, as amended, bore interest through maturity at a variable rate based on the three month SOFR Fourth Amendment . Interest expense related to the Pharmakon Loan Agreement was immaterial for the three and six months ended June 30, 2024. The Company recognized $1.6 million and $3.3 million of interest expense related to the Pharmakon Loan Agreement during the three and six months ended June 30, 2023, respectively. See Note 7, Indebtedness

DEFERRED REVENUE, REFUND LIABIL

DEFERRED REVENUE, REFUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES	6 Months Ended
	Jun. 30, 2024
Other Liabilities Disclosure [Abstract]
DEFERRED REVENUE, REFUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES	DEFERRED REVENUE, REFUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES The Company had the following deferred revenue balances as of June 30, 2024 (in thousands): June 30, 2024 Deferred Revenue: Short-Term Long-Term Total CSL Vifor License Agreement $ 43,296 — $ 43,296 Total $ 43,296 $ — $ 43,296 CSL Vifor License Agreement O n 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 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, or FMCNA , and its affiliates, including Fresenius Kidney Care Group LLC, to certain third-party dialysis organizations approved by the Company, to independent dialysis organizations that are 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 profits, 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 recorded as long-term deferred revenue in the accompanying unaudited condensed consolidated balance sheets. On July 10, 2024, the Company and CSL Vifor entered into a Termination and Settlement Agreement, or the Vifor Termination Agreement , pursuant to which the Company and CSL Vifor agreed, among other things, to terminate, effective immediately, the Vifor License Agreement. See Note 16, Subsequent Events , for further information on the Vifor Termination Agreement. 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 representing the premium over the closing stock price, or $4.7 million for the 2017 Shares and $13.6 million for the 2022 Shares, represents consideration related to the Vifor License Agreement. The 2017 Shares and 2022 Shares are subject to standstill agreement 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. See Note 8, Deferred Revenue, Refund Liability and Liability Related to the Sale of Future Royalties , of the Notes to the Consolidated Financial Statements in the 2023 Form 10-K for a more detailed description of the Vifor License Agreement. Deferred Revenue Recognition The Company evaluated the elements of the Vifor License Agreement in accordance with the provisions of ASC 606 and concluded that the contract counterparty, CSL Vifor, was a customer. The Company identified one performance obligation under the Vifor License Agreement at inception which was the non-sublicensable, non-transferrable license under certain of the Company's intellectual property to (i) sell Vafseo solely to the Supply Group, (ii) sell Vafseo to Designated Wholesalers solely for resale to members of the Supply Group, (iii) conduct medical affairs with respect to Vafseo in the U.S. in the field during the term of the Vifor License Agreement and (iv) use the Akebia trademark solely in connection with the sale of Vafseo. The transaction price of $43.3 million was 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. Under the Vifor License Agreement, these payments from CSL Vifor were non-refundable and non-creditable against any other amount due to the Company. In addition, if the Centers for Medicare & Medicaid Services, or CMS, determined that Vafseo was excluded from the Transitional Drug Add-on Payment Adjustment, or TDAPA , the Company had the right to terminate the Vifor License Agreement and would then be required to repay the up-front payment and the premiums paid by CSL Vifor on the 2017 Shares and the 2022 Shares. Given the previous uncertainty associated with a potential future approval of Vafseo by the FDA, and whether Vafseo would be included in certain reimbursement bundles by CMS, the Company constrained the entire transaction price at inception. As a result of the Vifor Termination Agreement, there are no remaining performance obligations under the Vifor License Agreement. Accordingly, the transaction price of $43.3 million was classified as short-term deferred revenue in the accompanying unaudited condensed consolidated balance sheets as of June 30, 2024. Refund Liability to Customer/Working Capital Fund 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 Company determined the Working Capital Fund did not represent an obligation to transfer goods or services to CSL Vifor in the future and thus under ASC 606 was recorded as a refund liability. The refund liability was considered a debt arrangement with zero coupon interest and the Company imputed interest on the refund 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 refund liability and a corresponding deferred gain on the condensed consolidated balance sheet. The discount on the refund liability was amortized to interest expense using the effective interest method over the expected term of the Vifor License Agreement. The deferred gain was amortized to interest income on a straight-line basis over the expected term of the Vifor License Agreement. The amortization of the discount was $0.9 million and $1.6 million for the three and six months ended June 30, 2024, respectively, and $0.9 million and $1.7 million for the three and six months ended June 30, 2023, respectively. The amortization of the deferred gain was $0.8 million and $1.7 million for the three and six months ended June 30, 2024, respectively, and $1.0 million and $2.0 million for the three and six months ended June 30, 2023, respectively. 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 will commence 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. The Company will reassess the effective rate at each reporting period. As of June 30, 2024, the $40.0 million refund liability is classified as a long-term liability based on management's estimated timing of the repayment of the refund liability to Vifor exceeding one-year. Liability Related to Sale of Future Royalties On February 25, 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 MTPC Territory , and such payments collectively the Royalty Interest Payments , in each case, payable to the Company under the MTPC Agreement. 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 MTPC Agreement. At the transaction date, the Company recorded 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 reassesses the effective interest rate and adjusts the rate prospectively as needed. The annual effective interest rate as of June 30, 2024 was 0% and, therefore the Company did not recognize any non-cash interest expense in the unaudited condensed consolidated statements of operations and comprehensive loss. As a result of its ongoing involvement in the cash flows related to the royalties and sales milestones in the MTPC Territory, the Company will continue to account for these royalties as non-cash royalty revenue which is reflected in license, collaboration and other revenue in the unaudited condensed consolidated statements of operations and comprehensive loss. See Note 8, Deferred Revenue, Refund Liability and Liability Related to Sale of Future Royalties , of the Notes to the Consolidated Financial Statements in the 2023 Form 10-K for a more detailed description of the Royalty Agreement. The Company paid $0.4 million and $0.9 million of royalties to HCR during the three and six months ended June 30, 2024, respectively, and $0.4 million and $1.0 million during the three and six months ended June 30, 2023, respectively. As of June 30, 2024 and December 31, 2023 the balances were as follows (in thousands): Liability related to sale of future royalties June 30, 2024 December 31, 2023 Current portion (included in accrued expenses and other current liabilities) $ 2,013 $ 2,048 Long-term portion 53,101 54,013 Total liability related to sale of future royalties $ 55,114 $ 56,061

LEASES

LEASES	6 Months Ended
	Jun. 30, 2024
Leases [Abstract]
LEASES	LEASES Cambridge Lease Under the Cambridge Lease, the Company leases approximately 65,167 square feet of office, storage and lab 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 lab space expires on September 11, 2026, with one two-year extension option available. 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 are not reasonably certain. The Cambridge Lease does not contain residual value guarantees. 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 or the effective date of any subsequent lease term extensions. As of June 30, 2024, the remaining lease term for the Cambridge Lease was 2.20 years. Operating lease costs were $1.2 million and $2.5 million for the three and six months ended June 30, 2024, respectively, and $1.4 million and $3.2 million for the three and six months ended June 30, 2023, respectively. Cash paid for amounts included in the measurement of operating lease liabilities was $1.4 million and $2.9 million for the three and six months ended June 30, 2024, respectively, and $1.4 million and $3.1 million for the three and six months ended June 30, 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 other long-term assets in the accompanying unaudited condensed consolidated balance sheets as of June 30, 2024 and December 31, 2023. Sublease and Former Boston Lease Previously, the Company leased 27,924 square feet of office space in Boston, Massachusetts, or 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 did not record any rental income for the three and six months ended June 30, 2024 and recorded no rental income and $0.3 million in rental income as other income in the unaudited condensed consolidated statements of operations and comprehensive loss during the three and six months ended June 30, 2023, respectively. In May 2023, pursuant to an Assignment and Assumption of Lease Agreement, or 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 unaudited condensed consolidated statements of operations and comprehensive loss of $0.5 million during the three and six months ended June 30, 2023. Future Lease Commitments Future commitments under the Cambridge Lease are as follows (in thousands): Operating Remainder of 2024 $ 2,876 2025 5,819 2026 3,613 Total lease commitments $ 12,308 Less: present value adjustment (830) Current and long-term operating lease liabilities $ 11,478

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	6 Months Ended
	Jun. 30, 2024
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 SA, 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 at a predetermined price. As of June 30, 2024, the Company is required to purchase a minimum quantity of drug substance for Auryxia annually at a total cost of approximately $21.4 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 excess firm commitment liability recorded in other long-term liabilities related to the Company's contractual purchase commitments with Siegfried was $3.6 million and $1.5 million as of June 30, 2024 and December 31, 2023, respectively. Patheon Manufacturing On March 11, 2020, the Company entered into a Supply Agreement with Patheon Inc., or Patheon, or the Patheon Agreement , under which Patheon will manufacture Vafseo drug product for commercial use under a volume-based pricing structure through June 30, 2025, 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 June 30, 2024, the Company had no minimum commitments with Patheon, however, as estimated global demand fluctuates, the Company may have 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 June 30, 2024, the Company has committed to purchase $11.1 million of Vafseo drug substance from WuXi STA through the end of 2024. On February 10, 2021, the Company entered into a Supply Agreement with WuXi STA, 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 February 10, 2025. The Vafseo drug product price is reviewed annually by the Company and WuXi STA. The Company will also reimburse 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. 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 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 have 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, totaling $15.0 million. The upfront payment of $17.5 million was made during the quarter ended December 31, 2022 and was recognized to 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 on 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 is being amortized to interest expense using the effective interest rate method over the term of the liability. The amortization of the discount was $0.4 million and $1.0 million for the three and six months ended June 30, 2024, respectively, and $0.5 million and $0.9 million for the three and six months ended June 30, 2023, respectively. In-Licensing - 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 with the right 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 the Company-owned patents, with the right 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. See Note 10, Commitments and Contingencies , of the Notes to the Consolidated Financial Statements in the 2023 Form 10-K for a more detailed description of this license agreement. The Company incurred royalty payments due to Panion of approximately $2.5 million and $4.3 million during the three and six months ended June 30, 2024, respectively, and $3.2 million and $6.0 million during the three and six months ended June 30, 2023, respectively, relating to the Company’s sales of Auryxia in the U.S. and JT and Torii’s net sales of Riona in Japan. Other Third-Party Contracts The Company contracts with various organizations to conduct R&D activities with remaining contract costs to the Company of approximately $46.7 million at June 30, 2024. The scope of the services under these R&D contracts can be modified and the contracts 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

PRODUCT REVENUE AND RESERVES FO

PRODUCT REVENUE AND RESERVES FOR VARIABLE CONSIDERATION	6 Months Ended
	Jun. 30, 2024
Revenue from Contract with Customer [Abstract]
PRODUCT REVENUE AND RESERVES FOR VARIABLE CONSIDERATION	PRODUCT REVENUE AND RESERVES FOR VARIABLE CONSIDERATION To date, the Company’s only source of product revenue has been from the U.S. sales of Auryxia. Total net product revenue was $41.2 million and $72.2 million for the three and six months ended June 30, 2024, respectively, and $42.2 million and $77.0 million for the three and six months ended June 30, 2023, respectively. Product revenue allowance and reserve categories were as follows: (in thousands) Chargebacks Rebates, Fees Product Returns Total Balance at December 31, 2023 $ 1,607 $ 22,991 $ 6,916 $ 31,514 Current provisions related to sales in current year 4,054 19,373 1,870 25,297 Adjustments related to prior year sales 77 (101) (105) (129) Credits/payments made (4,301) (27,530) (3,352) (35,183) Balance at June 30, 2024 $ 1,437 $ 14,733 $ 5,329 $ 21,499 (in thousands) Chargebacks Rebates, Fees Product Returns Total Balance at December 31, 2022 $ 1,259 $ 26,252 $ 10,923 $ 38,434 Current provisions related to sales in current year 5,215 38,998 2,566 46,779 Adjustments related to prior year sales (8) (473) (171) (652) Credits/payments made (5,617) (41,474) (5,442) (52,533) Balance at June 30, 2023 $ 849 $ 23,303 $ 7,876 $ 32,028 Chargebacks, discounts and estimated product returns are recorded as a reduction of revenue in the period the related product revenue is recognized in the unaudited condensed 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 on the condensed 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 unaudited condensed consolidated balance sheets. Accounts receivable, net related to product sales, was approximately $27.9 million and $35.9 million as of June 30, 2024 and December 31, 2023, respectively.

LICENSE, COLLABORATION AND OTHE

LICENSE, COLLABORATION AND OTHER REVENUE	6 Months Ended
	Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
LICENSE, COLLABORATION AND OTHER REVENUE	LICENSE, COLLABORATION AND OTHER REVENUE The Company recognized the following revenue from its license, collaboration and other revenue agreements (in thousands): Three Months Ended June 30, Six Months Ended June 30, Entity Description 2024 2023 2024 2023 Medice License and Product Supply of Vafseo in EU $ — $ 10,000 $ — $ 10,000 MTPC License and Product Supply of Vafseo in Japan 1,169 516 1,581 4,678 JT and Torii License and royalties related to the sale of Riona in Japan 1,270 1,391 2,456 2,528 Otsuka Terminated U.S. and International Agreements — 2,225 — 2,225 Total license and other revenue $ 2,439 $ 14,132 $ 4,037 $ 19,431 The following tables present changes in the Company’s contract assets and liabilities related to license and other revenue (in thousands): Six Months Ended June 30, 2024 Balance at Additions Deductions Balance Contract asset: Accounts receivable (1) $ 3,333 $ 4,037 $ (5,542) $ 1,828 Contract liability: Deferred revenue $ 43,296 $ 695 $ (695) $ 43,296 Six Months Ended June 30, 2023 Balance at Additions Deductions Balance Contract assets: Accounts receivable (1) $ 1,901 $ 943 $ (2,319) $ 525 Prepaid expenses and other current assets $ 781 $ — $ (781) $ — Contract liabilities: Deferred revenue $ 47,034 $ — $ (3,738) $ 43,296 (1) Excludes accounts receivable related to amounts due to the Company from product sales of Auryxia which are included in the accompanying unaudited condensed consolidated balance sheets as of June 30, 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): Three Months Ended June 30, Six Months Ended June 30, Revenue Recognized in the Period: 2024 2023 2024 2023 Deferred revenue — beginning of the period $ — $ — $ — $ 3,738 During each of the three and six months ended June 30, 2024 and 2023, the Company recognized no revenue from performance obligations satisfied in previous periods. Medice License Agreement On May 24, 2023, or 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 market and sell Vafseo for the treatment of anemia in adult patients with CKD in 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 606-10-15, Revenue from Contracts with Customers – Scope and Scope Exceptions . 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 Medice License Agreement provides that the Company and Medice will enter into a supply agreement pursuant to which the Company will supply Vafseo to Medice for commercial use in the Medice Territory. As of June 30, 2024, the Company and Medice have not yet entered into a supply agreement. 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 is included in prepaid expenses and other current assets as of June 30, 2024 and other long-term assets as of December 31, 2023 on the unaudited condensed consolidated balance sheets. 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 unaudited condensed consolidated statements of operations and comprehensive loss during the three and six months ended June 30, 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. 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 recognizes revenue under this arrangement when risk of loss passes to Medice and delivery has occurred. As of June 30, 2024, there were immaterial accounts receivable and no contract assets, payables or deferred revenue recorded in connection with the Medice Letter Agreement. MTPC Collaboration Agreement On December 11, 2015, the Company and MTPC entered into a Collaboration Agreement, or the MTPC Agreement , providing MTPC with exclusive development and commercialization rights to Vafseo in the MTPC Territory, which was amended effective as of December 2, 2022. In addition, the Company supplies Vafseo to MTPC for both clinical and commercial use in the MTPC 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 MTPC Agreement, subject to certain caps and other terms and conditions. See Note 8, Deferred Revenue, Refund Liability and Liability Related to Sale of Future Royalties , for additional information and Note 12, License, Collaboration and Other Revenue , of the Notes to the Consolidated Financial Statements in the 2023 Form 10-K for a more detailed description of the MTPC Agreement. The Company evaluated the elements of the MTPC Agreement in accordance with the provisions of ASC 606 and concluded that the contract counterparty, MTPC, is a customer. The Company identified two performance obligations in connection with its material promises under the MTPC 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 MTPC for the Phase 3 studies, (iv) $10.0 million in development milestones received, (v) $25.0 million in regulatory milestones received and (vi) $5.9 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 June 30, 2024, all development milestones and $25.0 million in regulatory milestones have been achieved. No other regulatory milestones have been assessed as probable of being achieved and as a result have been fully constrained. 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 MTPC Agreement is being recognized using a proportional performance method, for which all deliverables have been completed. The Company recognizes any revenue from MTPC royalties in the period in which the sales occur. The Company recognized $0.5 million and $0.9 million of revenue from MTPC royalties during each of the three and six months ended June 30, 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 MTPC Agreement, subject to certain caps and other terms and conditions. See Note 8, Deferred Revenue, Refund Liability and Liability Related to Sale of Future Royalties , for additional information. The revenue is classified as license and other revenue in the accompanying unaudited condensed consolidated statements of operations and comprehensive loss. As of June 30, 2024, there were no accounts receivable, payables or deferred revenue and $0.5 million in contract assets recorded in connection with the MTPC Agreement. Supply of Drug Product to MTPC On July 15, 2020, the Company and MTPC entered into a supply agreement, or MTPC Supply Agreement , under which the Company supplies Vafseo drug product to MTPC for commercial use in Japan and certain other Asian countries, as contemplated by the MTPC Agreement. See Note 12, License, Collaboration and Other Revenue , of the Notes to the Consolidated Financial Statements in the 2023 Form 10-K for a more detailed description of this supply agreement. On December 16, 2022, the Company, MTPC and Esteve Química, S.A., or Esteve, executed an Assignment of Supply Agreement, or Esteve Assignment Agreement , pursuant to which the Supply Agreement between the Company and Esteve, or Esteve Agreement was assigned to MTPC. The Esteve Assignment Agreement transferred the rights and obligations of the Company under the Esteve Agreement to MTPC. The Company has no further obligation to take delivery of, or pay for, product delivered by Esteve. The Company does not recognize revenue under this arrangement until risk of loss on the drug product passes to MTPC and delivery has occurred and MTPC has accepted the product. The Company recognized $0.7 million in revenue under the MTPC Supply Agreement during the three and six months ended June 30, 2024, and no revenue and $3.7 million in revenue under the MTPC Supply Agreement during the three and six months ended June 30, 2023, respectively. As of June 30, 2024, there were no accounts receivable, deferred revenue or other current liabilities relating to the MTPC 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 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. See Note 12, License, Collaboration and Other Revenue , of the Notes to the Consolidated Financial Statements in the 2023 Form 10-K for a more detailed description of this sublicense agreement. 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 allocated the entire transaction price to the License and Supply Performance Obligation. The Company recognized license revenue of $1.3 million and $2.5 million during the three and six months ended June 30, 2024, respectively, and $1.4 million and $2.5 million during the three and six months ended June 30, 2023, respectively, related to royalties earned on net sales of ferric citrate hydrate in Japan under the trade name Riona. 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.

CAPITAL STOCK

CAPITAL STOCK	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
CAPITAL STOCK	CAPITAL STOCK Authorized and Outstanding Capital Stock On June 5, 2020, the Company filed a Certificate of Amendment to its Ninth Amended and Restated Certificate of Incorporation, or its Charter , to increase the number of authorized shares of common stock from 175,000,000 to 350,000,000. As of June 30, 2024, the authorized capital stock of the Company included 350,000,000 shares of common stock, $0.00001 par value per share, of which 209,929,145 and 194,582,539 shares were issued and outstanding as of June 30, 2024 and December 31, 2023, respectively; and 25,000,000 shares of undesignated preferred stock, $0.00001 par value per share, of which no shares were issued and outstanding as of June 30, 2024 and December 31, 2023. At-the-Market Facility On April 7, 2022, the Company entered into an at-the-market, or ATM , sales agreement with Jefferies LLC, or Jefferies,

STOCK-BASED COMPENSATION AND BE

STOCK-BASED COMPENSATION AND BENEFIT PLAN	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
STOCK-BASED COMPENSATION AND BENEFIT PLAN	STOCK-BASED COMPENSATION AND BENEFIT PLAN Stock-Based Compensation and Benefit Plans The Company incurred stock-based compensation expenses of $2.1 million and $4.4 million for the three and six months ended June 30, 2024, respectively, and $3.5 million and $6.0 million for the three and six months ended June 30, 2023, respectively. Equity Incentive Plans The following table contains information about the Company's equity plans: June 30, 2024 December 31, 2023 Title of Plan Group Eligible Type of Award Granted (or to be Granted) Awards Outstanding Additional Awards Authorized for Grant Awards Outstanding Additional Awards Authorized for Grant Keryx Equity Plans (1)(2) Employees, directors and consultants Stock options and RSUs 208,986 — 232,203 — Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (2) (3) ( the 2014 Plan ) Employees, directors, consultants and advisors Stock options, RSUs, SARs and performance awards 12,597,753 — 15,311,501 — Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (3) ( the 2023 Plan ) (replaced 2014 Plan) Employees, officers, directors, consultants and advisors Stock options, SARs, restricted stock, unrestricted stock, RSUs, performance awards, other share-based awards and dividend equivalents 10,435,850 — 1,712,400 17,382,722 (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 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: 1,496,428 options included as outstanding under the 2014 Plan in the table and 2,374,950 options included as outstanding under the 2023 Plan in the table as of June 30, 2024 and 1,616,019 options included as outstanding under the 2014 Plan and 794,000 options included as outstanding under the 2023 Plan in the table as of December 31, 2023. Common Stock Options and Stock Appreciation Rights During the six months ended June 30, 2024, the Company issued 3,432,500 options to employees 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 six months ended June 30, 2024, the Company granted 1,604,950 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 1,604,950 options remained outstanding as of June 30, 2024. The Company grants annual service-based stock options to employees and directors and SARs to certain executives under the 2023 and 2014 Plans. In addition, the Company issues stock options to directors, new hires and occasionally to other employees not in connection with the annual grant process. Finally, the Company 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 six months ended June 30, 2024, is as follows: Stock Weighted Average Exercise Price Weighted-Average Contractual Life (years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2023 13,312,835 $ 4.20 7.27 years — Granted 5,037,450 $ 1.57 — — Exercised (304,152) $ 0.51 — — Expired (119,043) $ 21.02 Canceled and forfeited (648,270) $ 3.11 — — Outstanding at June 30, 2024 17,278,820 $ 3.42 7.37 years $ 1,521 Exercisable at June 30, 2024 8,559,257 $ 5.40 5.59 years As of June 30, 2024, there was approximately $9.3 million of unrecognized compensation costs related to stock options, which is expected to be recognized over a weighted average period of 2.94 years. Restricted Stock Units Generally, restricted stock units, or 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, or (iii) 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. RSU and PSU activity is as follows: 2014 Plan 2023 Plan Number of Shares Weighted Average Fair Value Number of Shares Weighted Average Fair Value Outstanding as of December 31, 2023 3,339,869 $ 1.30 603,400 $ 1.48 Granted — $ — 3,968,200 $ 1.59 Vested (1,478,822) $ 1.62 (210,000) $ 1.20 Forfeited and canceled (210,678) $ 0.90 (48,200) $ 1.68 Outstanding as of June 30, 2024 1,650,369 $ 1.07 4,313,400 $ 1.59 As of June 30, 2024, there was $7.3 million of unrecognized compensation costs related to time-based RSUs and PSUs, which is expected to be recognized over a weighted-average period of 2.25 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 offering period. As of June 30, 2024 and December 31, 2023, a total of 4,545,480 and 4,637,801 shares of the Company’s common stock were available for future issuance under the ESPP, respectively. The Company issued 92,321 shares under the ESPP during the six months ended June 30, 2024. Stock-Based Compensation Expense The Black-Scholes option pricing model is used to estimate the fair value of the 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: Three Months Ended June 30, Six Months Ended June 30, Stock Options 2024 2023 2024 2023 Risk-free interest rate 4.24 % - 4.66% 3.67 % - 3.99% 3.90% - 4.66% 3.54% - 3.99% Expected volatility 109.98 % - 118.61% 102.31 % - 111.71% 109.98% - 118.61% 100.97% - 111.71% Expected term (years) 5.51 years - 6.25 years 5.51 years - 6.25 years 5.51 years - 6.25 years 5.51 years - 6.25 years Expected dividend yield —% —% —% —% Weighted average grant date fair value $0.91 $0.97 $1.35 $0.56 The Company has classified stock-based compensation in its unaudited condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Cost of goods sold $ 83 $ 73 $ 169 $ 139 Research and development 396 532 815 1,202 Selling, general and administrative 1,593 2,685 3,410 4,220 Restructuring — 200 38 418 Total stock-based compensation $ 2,072 $ 3,490 $ 4,432 $ 5,979

NET LOSS PER SHARE

NET LOSS PER SHARE	6 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE Potentially dilutive securities, warrants, common stock options, RSUs and SARs 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: Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Warrants (1) 3,076,923 — 3,076,923 — Outstanding common stock options 16,643,507 13,118,185 16,643,507 13,118,185 Unvested RSUs 5,963,769 4,596,551 5,963,769 4,596,551 Stock appreciation rights 635,313 635,313 635,313 635,313 Total 26,319,512 18,350,049 26,319,512 18,350,049

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	6 Months Ended
	Jun. 30, 2024
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 Quarterly Report on Form 10-Q with the SEC, to ensure that the unaudited condensed consolidated financial statements include appropriate disclose of events both recognized in the accompanying unaudited condensed consolidated financial statements as of June 30, 2024, 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: CSL Vifor Termination and Settlement 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 which the Company granted to CSL Vifor an exclusive license to sell Vafseo to the Supply Group in the U.S. Under the Vifor License Agreement, CSL Vifor contributed $40.0 million to the Working Capital Fund, established to partially fund the Company’s costs of purchasing Vafseo from its contract manufacturers. Pursuant to the terms of the Vifor Termination Agreement, and generally consistent with the terms of the Vifor License Agreement, as amended, the Company has agreed to repay the Working Capital Fund to CSL Vifor through the WCF Royalty Payments. The WCF Royalty Payments will commence 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. See Note 8, Deferred Revenue, Refund Liability and Liability Related to Sale of Future Royalties , for further information on the repayment of the Working Capital Fund. In addition, 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 will commence upon the first sale of Vafseo by the Company, its affiliates or third-party licensees 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 will continue as described above. The WCF Royalty Payments, 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. Amendment to BlackRock Credit Agreement On July 10, 2024, in connection with the Vifor Termination Agreement, the Company and Kreos entered into the BlackRock Credit Amendment. The BlackRock Credit Amendment includes certain covenants of the Company related to the Vifor Termination Agreement. See Note 7, Indebtedness

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net loss	$ (8,582)	$ (17,985)	$ (11,172)	$ (26,876)	$ (26,567)	$ (38,050)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended	6 Months Ended
	Jun. 30, 2024 shares	Jun. 30, 2024 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		The following table describes, for the second quarter of 2024, each trading arrangement for the sale or purchase of Company securities adopted or terminated by our directors and officers that is either (1) a contract, instruction or written plan intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) (a “Rule 10b5-1 trading arrangement”) or (2) a “non-Rule 10b5-1 trading arrangement” (as defined in Item 408(c) of Regulation S-K): Name (Title) Action Taken (Date of Action) Type of Trading Arrangement Nature of Trading Arrangement Duration of Trading Arrangement Aggregate Number of Securities Erik J. Ostrowski (Senior Vice President, Chief Financial Officer, Chief Business Officer and Treasurer) Adoption (June 21, 2024) Durable Rule 10b5-1 trading arrangement for sell-to-cover transactions relating to all equity awards that have or may be granted Sale Until final settlement of any restricted stock units, or RSUs Indeterminable (1) Nicholas Grund (Senior Vice President, Chief Commercial Officer) Adoption (May 13, 2024) Durable Rule 10b5-1 trading arrangement for sell-to-cover transactions relating to all equity awards that have or may be granted Sale Until final settlement of any RSUs Indeterminable (1) Michel Dahan (Former Senior Vice President, Chief Operating Officer) Adoption (May 31, 2024) Rule 10b5-1 Non-Discretionary Option Exercise and Stock Sale Plan Sale Until March 31, 2025 Up to an aggregate of 823,166 shares (1) The number of shares subject to RSUs that will be sold to satisfy applicable tax withholding obligations upon vesting is unknown as the number will vary based on the extent to which vesting conditions are satisfied, the market price of the Company’s common stock at the time of settlement and the potential future grant of additional RSUs subject to this arrangement. This trading arrangement, which applies to RSUs whether vesting is based on the passage of time and/or the achievement of performance goals, provides for the automatic sale of shares that would otherwise be issuable on each settlement date of a RSU in an amount sufficient to satisfy the applicable tax withholding obligation, with the proceeds of the sale delivered to the Company in satisfaction of the applicable tax withholding obligation.
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Erik J. Ostrowski [Member]
Trading Arrangements, by Individual
Name	Erik J. Ostrowski
Title	Senior Vice President, Chief Financial Officer, Chief Business Officer and Treasurer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	Adoption(June 21, 2024)
Nicholas Grund [Member]
Trading Arrangements, by Individual
Name	Nicholas Grund
Title	Senior Vice President, Chief Commercial Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	Adoption(May 13, 2024)
Michel Dahan [Member]
Trading Arrangements, by Individual
Name	Michel Dahan
Title	Former Senior Vice President, Chief Operating Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	Adoption (May 31, 2024)
Expiration Date	March 31, 2025
Arrangement Duration	304 days
Aggregate Available	823,166	823,166

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation and Principles of Consolidation The accompanying unaudited condensed 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 unaudited condensed 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	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 unaudited condensed consolidated financial statements include, but are not limited to: accrued expenses, other long-term liabilities, product revenues, including various rebates, returns and reserves 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, intangible asset and goodwill.
Cash, Cash Equivalents and Restricted Cash	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 June 30, 2024, cash and cash equivalents primarily included cash on hand. 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 “other long-term assets” in the consolidated balance sheets.
Concentration of Credit Risk	Concentration of 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. The Company's allowance for credit losses was $0.2 million and $1.0 million as of June 30, 2024 and December 31, 2023, respectively. For the six months ended June 30, 2024, net recoveries were $0.2 million, inclusive of an incremental allowance for credit losses of $0.2 million for the three months ended June 30, 2024. Write-offs were $0.6 million for the three and six months ended June 30, 2023. 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 product 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 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 active pharmaceutical ingredients and formulated drugs or distribution of finished product to the market.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In November 2023, the FASB issued ASU 2023-07, Improvements to Reportable Segment Disclosures . ASU 2023-07 requires disclosure of significant segment expenses that are regularly provided to the chief operating decision maker, or CODM, and included within the segment measure of profit or loss, an amount and description of its composition for other segment items to reconcile to segment profit or loss, and the title and position of the entity’s CODM. ASU 2023-07 will be applied retrospectively and is effective for annual reporting periods in fiscal years beginning after December 15, 2023, and interim reporting periods in fiscal years beginning after December 31, 2024. The Company is currently reviewing the impact that the adoption of ASU 2023-07 may have on its consolidated financial statements and disclosure. 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 will be effective for the annual reporting periods in fiscal years beginning after December 15, 2024. The Company is currently evaluating ASU 2023-09 and does not expect it to have a material effect on the Company’s consolidated financial statements.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	6 Months Ended
	Jun. 30, 2024
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 showing in the consolidated statements of cash flows: (in thousands) June 30, 2024 December 31, 2023 Cash and cash equivalents $ 39,499 $ 42,925 Restricted cash included in other long-term assets 1,668 1,654 Total cash, cash equivalents and restricted cash $ 41,167 $ 44,579
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 showing in the consolidated statements of cash flows: (in thousands) June 30, 2024 December 31, 2023 Cash and cash equivalents $ 39,499 $ 42,925 Restricted cash included in other long-term assets 1,668 1,654 Total cash, cash equivalents and restricted cash $ 41,167 $ 44,579

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
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): June 30, 2024 Level 1 Level 2 Level 3 Total Fair Value Long-term liability: Warrant liability $ — $ 2,644 $ — $ 2,644 December 31, 2023 Level 1 Level 2 Level 3 Total Fair Value Cash equivalents: Money market funds $ 1,504 $ — $ — $ 1,504

INVENTORIES AND PREPAID MANUF_2

INVENTORIES AND PREPAID MANUFACTURING (Tables)	6 Months Ended
	Jun. 30, 2024
Inventory Disclosure [Abstract]
Inventory Components	Inventories consists of the following (in thousands): June 30, 2024 December 31, 2023 Inventories, current: Work-in-process $ 9,547 $ 4,297 Finished goods 14,325 11,394 Inventories, current $ 23,872 $ 15,691 Long-term inventories included in other long-term assets: Raw materials 403 1,143 Work-in-process 14,795 8,260 Inventories, long-term 15,198 9,403 Total inventories $ 39,070 $ 25,094

INTANGIBLE ASSET AND GOODWILL (

INTANGIBLE ASSET AND GOODWILL (Tables)	6 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible asset, net of accumulated amortization, prior impairments and adjustments as of June 30, 2024 and December 31, 2023 consisted of the following (in thousands): June 30, 2024 December 31, 2023 Intangible asset: Gross Carrying Accumulated Amortization Net Book Value Net Book Value Estimated Useful Life Developed product rights for Auryxia $ 214,705 $ (196,684) $ 18,021 $ 36,042 6 years

ADDITIONAL BALANCE SHEET DETA_2

ADDITIONAL BALANCE SHEET DETAIL (Tables)	6 Months Ended
	Jun. 30, 2024
Payables and Accruals [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets are as follows (in thousands): Description June 30, 2024 December 31, 2023 Prepaid manufacturing $ 11,632 $ 14,489 Other 7,329 5,754 Total prepaid expenses and other current assets $ 18,961 $ 20,243
Schedule of Other Long-Term Assets	Other long-term assets are as follows (in thousands): Description June 30, 2024 December 31, 2023 Long-term inventories $ 15,198 $ 9,403 Restricted cash 1,668 1,654 Other 913 1,366 Total other long-term assets $ 17,779 $ 12,423
Components of Accrued Expenses	Accrued expenses and other current liabilities consists of the following (in thousands): Description June 30, 2024 December 31, 2023 Product revenue allowances $ 14,733 $ 22,940 Product return reserves, current portion 4,337 5,420 Clinical trial costs 227 328 Compensation and related benefits 6,364 8,216 Operating lease liabilities, current portion 5,179 4,491 Royalties due to Panion & BF Biotech, Inc. 3,260 3,989 Professional fees 1,485 1,909 Accrued manufacturing costs 1,165 5,555 Restructuring costs, current portion 723 737 BioVectra, Inc. termination fees, current portion 10,000 7,500 Liability related to sale of future royalties, current portion 2,013 2,048 Other 4,411 4,602 Total accrued expenses and other current liabilities $ 53,897 $ 67,735

INDEBTEDNESS (Tables)

INDEBTEDNESS (Tables)	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Schedule of Future Principal Payments on the Term Loans	As of June 30, 2024, future principal payments under the BlackRock Credit Agreement are as follows (in thousands): Principal Payments 2024 $ — 2025 — 2026 — 2027 41,363 2028 1,589 Total before unamortized discount and issuance costs 42,952 Less: unamortized discount and issuance costs (4,921) Total term loans $ 38,031

DEFERRED REVENUE, REFUND LIAB_2

DEFERRED REVENUE, REFUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES (Tables)	6 Months Ended
	Jun. 30, 2024
Other Liabilities Disclosure [Abstract]
Summary of Deferred Revenue Balances	The Company had the following deferred revenue balances as of June 30, 2024 (in thousands): June 30, 2024 Deferred Revenue: Short-Term Long-Term Total CSL Vifor License Agreement $ 43,296 — $ 43,296 Total $ 43,296 $ — $ 43,296 The following tables present changes in the Company’s contract assets and liabilities related to license and other revenue (in thousands): Six Months Ended June 30, 2024 Balance at Additions Deductions Balance Contract asset: Accounts receivable (1) $ 3,333 $ 4,037 $ (5,542) $ 1,828 Contract liability: Deferred revenue $ 43,296 $ 695 $ (695) $ 43,296 Six Months Ended June 30, 2023 Balance at Additions Deductions Balance Contract assets: Accounts receivable (1) $ 1,901 $ 943 $ (2,319) $ 525 Prepaid expenses and other current assets $ 781 $ — $ (781) $ — Contract liabilities: Deferred revenue $ 47,034 $ — $ (3,738) $ 43,296 (1) Excludes accounts receivable related to amounts due to the Company from product sales of Auryxia which are included in the accompanying unaudited condensed consolidated balance sheets as of June 30, 2024 and 2023.
Liability Related to Sale of Future Royalties	As of June 30, 2024 and December 31, 2023 the balances were as follows (in thousands): Liability related to sale of future royalties June 30, 2024 December 31, 2023 Current portion (included in accrued expenses and other current liabilities) $ 2,013 $ 2,048 Long-term portion 53,101 54,013 Total liability related to sale of future royalties $ 55,114 $ 56,061

LEASES (Tables)

LEASES (Tables)	6 Months Ended
	Jun. 30, 2024
Leases [Abstract]
Future Commitments under Non-Cancelable Leases	Future commitments under the Cambridge Lease are as follows (in thousands): Operating Remainder of 2024 $ 2,876 2025 5,819 2026 3,613 Total lease commitments $ 12,308 Less: present value adjustment (830) Current and long-term operating lease liabilities $ 11,478

PRODUCT REVENUE AND RESERVES _2

PRODUCT REVENUE AND RESERVES FOR VARIABLE CONSIDERATION (Tables)	6 Months Ended
	Jun. 30, 2024
Revenue from Contract with Customer [Abstract]
Product Revenue Allowance and Reserve Categories	Product revenue allowance and reserve categories were as follows: (in thousands) Chargebacks Rebates, Fees Product Returns Total Balance at December 31, 2023 $ 1,607 $ 22,991 $ 6,916 $ 31,514 Current provisions related to sales in current year 4,054 19,373 1,870 25,297 Adjustments related to prior year sales 77 (101) (105) (129) Credits/payments made (4,301) (27,530) (3,352) (35,183) Balance at June 30, 2024 $ 1,437 $ 14,733 $ 5,329 $ 21,499 (in thousands) Chargebacks Rebates, Fees Product Returns Total Balance at December 31, 2022 $ 1,259 $ 26,252 $ 10,923 $ 38,434 Current provisions related to sales in current year 5,215 38,998 2,566 46,779 Adjustments related to prior year sales (8) (473) (171) (652) Credits/payments made (5,617) (41,474) (5,442) (52,533) Balance at June 30, 2023 $ 849 $ 23,303 $ 7,876 $ 32,028

LICENSE, COLLABORATION AND OT_2

LICENSE, COLLABORATION AND OTHER REVENUE (Tables)	6 Months Ended
	Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenues Recognized from License, Collaboration and Other Significant Agreements	The Company recognized the following revenue from its license, collaboration and other revenue agreements (in thousands): Three Months Ended June 30, Six Months Ended June 30, Entity Description 2024 2023 2024 2023 Medice License and Product Supply of Vafseo in EU $ — $ 10,000 $ — $ 10,000 MTPC License and Product Supply of Vafseo in Japan 1,169 516 1,581 4,678 JT and Torii License and royalties related to the sale of Riona in Japan 1,270 1,391 2,456 2,528 Otsuka Terminated U.S. and International Agreements — 2,225 — 2,225 Total license and other revenue $ 2,439 $ 14,132 $ 4,037 $ 19,431
Changes in Contract Assets and Liabilities	The Company had the following deferred revenue balances as of June 30, 2024 (in thousands): June 30, 2024 Deferred Revenue: Short-Term Long-Term Total CSL Vifor License Agreement $ 43,296 — $ 43,296 Total $ 43,296 $ — $ 43,296 The following tables present changes in the Company’s contract assets and liabilities related to license and other revenue (in thousands): Six Months Ended June 30, 2024 Balance at Additions Deductions Balance Contract asset: Accounts receivable (1) $ 3,333 $ 4,037 $ (5,542) $ 1,828 Contract liability: Deferred revenue $ 43,296 $ 695 $ (695) $ 43,296 Six Months Ended June 30, 2023 Balance at Additions Deductions Balance Contract assets: Accounts receivable (1) $ 1,901 $ 943 $ (2,319) $ 525 Prepaid expenses and other current assets $ 781 $ — $ (781) $ — Contract liabilities: Deferred revenue $ 47,034 $ — $ (3,738) $ 43,296 (1) Excludes accounts receivable related to amounts due to the Company from product sales of Auryxia which are included in the accompanying unaudited condensed consolidated balance sheets as of June 30, 2024 and 2023.
Revenue Recognized Resulting from Changes in Contract Assets and Contract Liabilities	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): Three Months Ended June 30, Six Months Ended June 30, Revenue Recognized in the Period: 2024 2023 2024 2023 Deferred revenue — beginning of the period $ — $ — $ — $ 3,738

STOCK-BASED COMPENSATION AND _2

STOCK-BASED COMPENSATION AND BENEFIT PLAN (Tables)	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Equity Plans	The following table contains information about the Company's equity plans: June 30, 2024 December 31, 2023 Title of Plan Group Eligible Type of Award Granted (or to be Granted) Awards Outstanding Additional Awards Authorized for Grant Awards Outstanding Additional Awards Authorized for Grant Keryx Equity Plans (1)(2) Employees, directors and consultants Stock options and RSUs 208,986 — 232,203 — Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (2) (3) ( the 2014 Plan ) Employees, directors, consultants and advisors Stock options, RSUs, SARs and performance awards 12,597,753 — 15,311,501 — Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (3) ( the 2023 Plan ) (replaced 2014 Plan) Employees, officers, directors, consultants and advisors Stock options, SARs, restricted stock, unrestricted stock, RSUs, performance awards, other share-based awards and dividend equivalents 10,435,850 — 1,712,400 17,382,722 (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 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: 1,496,428 options included as outstanding under the 2014 Plan in the table and 2,374,950 options included as outstanding under the 2023 Plan in the table as of June 30, 2024 and 1,616,019 options included as outstanding under the 2014 Plan and 794,000 options included as outstanding under the 2023 Plan in the table as of December 31, 2023.
Stock Option Activity	The combined stock option activity for the six months ended June 30, 2024, is as follows: Stock Weighted Average Exercise Price Weighted-Average Contractual Life (years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2023 13,312,835 $ 4.20 7.27 years — Granted 5,037,450 $ 1.57 — — Exercised (304,152) $ 0.51 — — Expired (119,043) $ 21.02 Canceled and forfeited (648,270) $ 3.11 — — Outstanding at June 30, 2024 17,278,820 $ 3.42 7.37 years $ 1,521 Exercisable at June 30, 2024 8,559,257 $ 5.40 5.59 years
RSU and PSU Activity	RSU and PSU activity is as follows: 2014 Plan 2023 Plan Number of Shares Weighted Average Fair Value Number of Shares Weighted Average Fair Value Outstanding as of December 31, 2023 3,339,869 $ 1.30 603,400 $ 1.48 Granted — $ — 3,968,200 $ 1.59 Vested (1,478,822) $ 1.62 (210,000) $ 1.20 Forfeited and canceled (210,678) $ 0.90 (48,200) $ 1.68 Outstanding as of June 30, 2024 1,650,369 $ 1.07 4,313,400 $ 1.59
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: Three Months Ended June 30, Six Months Ended June 30, Stock Options 2024 2023 2024 2023 Risk-free interest rate 4.24 % - 4.66% 3.67 % - 3.99% 3.90% - 4.66% 3.54% - 3.99% Expected volatility 109.98 % - 118.61% 102.31 % - 111.71% 109.98% - 118.61% 100.97% - 111.71% Expected term (years) 5.51 years - 6.25 years 5.51 years - 6.25 years 5.51 years - 6.25 years 5.51 years - 6.25 years Expected dividend yield —% —% —% —% Weighted average grant date fair value $0.91 $0.97 $1.35 $0.56
Stock-Based Compensation Expense in Consolidated Statement of Operations and Comprehensive Loss	The Company has classified stock-based compensation in its unaudited condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Cost of goods sold $ 83 $ 73 $ 169 $ 139 Research and development 396 532 815 1,202 Selling, general and administrative 1,593 2,685 3,410 4,220 Restructuring — 200 38 418 Total stock-based compensation $ 2,072 $ 3,490 $ 4,432 $ 5,979

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	6 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
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: Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Warrants (1) 3,076,923 — 3,076,923 — Outstanding common stock options 16,643,507 13,118,185 16,643,507 13,118,185 Unvested RSUs 5,963,769 4,596,551 5,963,769 4,596,551 Stock appreciation rights 635,313 635,313 635,313 635,313 Total 26,319,512 18,350,049 26,319,512 18,350,049

NATURE OF BUSINESS (Details)

NATURE OF BUSINESS (Details) $ in Thousands	Jun. 30, 2024 USD ($) product	Dec. 31, 2023 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of commercial products | product	2
Cash and cash equivalents | $	$ 39,499	$ 42,925

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reconciliations (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 39,499	$ 42,925
Restricted cash included in other long-term assets	1,668	1,654
Total cash, cash equivalents and restricted cash	$ 41,167	$ 44,579	$ 55,294	$ 93,169

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($) financial_institution	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) financial_institution	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Accounting Policies [Abstract]
Number of financial institutions maintaining cash | financial_institution	2		2
Allowance for credit loss	$ 0.2		$ 0.2		$ 1
Allowance for credit loss, writeoff	$ 0.2	$ 0.6	$ 0.2	$ 0.6

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS - Assets Measured or Disclosed at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability	$ 2,600
Fair value measurements recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability	2,644
Money market funds		$ 1,504
Fair value measurements recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability	0
Money market funds		1,504
Fair value measurements recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability	2,644
Money market funds		0
Fair value measurements recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liability	$ 0
Money market funds		$ 0

INVENTORIES AND PREPAID MANUF_3

INVENTORIES AND PREPAID MANUFACTURING - Components of Inventory (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Inventory [Line Items]
Finished goods	$ 14,325	$ 11,394
Inventories, current	23,872	15,691
Raw materials	403	1,143
Inventories, long-term	15,198	9,403
Total inventories	39,070	25,094
Inventories
Inventory [Line Items]
Work-in-process	9,547	4,297
Other Noncurrent Assets
Inventory [Line Items]
Work-in-process	$ 14,795	$ 8,260

INVENTORIES AND PREPAID MANUF_4

INVENTORIES AND PREPAID MANUFACTURING - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Inventory [Line Items]
Write-down of inventory			$ 1,061	$ 612
Benefit in cost of goods sold related to previously written down as excess inventory	$ 4,900		8,600
Auryxia Drug Substance
Inventory [Line Items]
Prepaid manufacturing costs	0		0		$ 500
Write-down of inventory	500	$ 300	1,100	$ 600
Vadadustat Drug Substance
Inventory [Line Items]
Prepaid manufacturing costs	$ 11,600		$ 11,600		$ 14,000

INTANGIBLE ASSET AND GOODWILL -

INTANGIBLE ASSET AND GOODWILL - Intangible Assets (Details) - Developed product rights for Auryxia - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 214,705
Accumulated Amortization	(196,684)
Net Book Value	$ 18,021	$ 36,042
Estimated Useful Life	6 years

INTANGIBLE ASSET AND GOODWILL_2

INTANGIBLE ASSET AND GOODWILL - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 9,000,000	$ 9,000,000	$ 18,021,000	$ 18,021,000
Goodwill	59,044,000		59,044,000		$ 59,044,000
Goodwill, accumulated impairment losses	$ 0		$ 0

ADDITIONAL BALANCE SHEET DETA_3

ADDITIONAL BALANCE SHEET DETAIL - Schedule of Prepaids and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Prepaid manufacturing	$ 11,632	$ 14,489
Other	7,329	5,754
Total prepaid expenses and other current assets	$ 18,961	$ 20,243

ADDITIONAL BALANCE SHEET DETA_4

ADDITIONAL BALANCE SHEET DETAIL - Schedule of Other Long-Term Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Raw materials	$ 15,198	$ 9,403
Restricted cash	1,668	1,654
Other	913	1,366
Total other long-term assets	$ 17,779	$ 12,423

ADDITIONAL BALANCE SHEET DETA_5

ADDITIONAL BALANCE SHEET DETAIL - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Payables and Accruals [Abstract]
Capitalized implementation costs	$ 900,000		$ 900,000		$ 0
Capitalized implementation costs, amortization expense	$ 0	$ 0	$ 0	$ 0

ADDITIONAL BALANCE SHEET DETA_6

ADDITIONAL BALANCE SHEET DETAIL - Summary of Accrued Expenses and other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Product revenue allowances	$ 14,733	$ 22,940
Product return reserves, current portion	4,337	5,420
Clinical trial costs	227	328
Compensation and related benefits	$ 6,364	$ 8,216
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Total accrued expenses and other current liabilities	Total accrued expenses and other current liabilities
Operating lease liabilities, current portion	$ 5,179	$ 4,491
Royalties due to Panion & BF Biotech, Inc.	3,260	3,989
Professional fees	1,485	1,909
Accrued manufacturing costs	1,165	5,555
Restructuring costs, current portion	723	737
BioVectra, Inc. termination fees, current portion	10,000	7,500
Liability related to sale of future royalties, current portion	2,013	2,048
Other	4,411	4,602
Total accrued expenses and other current liabilities	$ 53,897	$ 67,735

INDEBTEDNESS - Narrative (Detai

INDEBTEDNESS - Narrative (Details) $ / shares in Units, $ in Thousands						3 Months Ended		6 Months Ended
	Apr. 19, 2024 USD ($)	Jan. 29, 2024 USD ($) tranche $ / shares shares	Jul. 15, 2022	Dec. 10, 2020 USD ($)	Nov. 25, 2019 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2024 $ / shares shares	Nov. 11, 2019 USD ($) tranche
Line of Credit Facility [Line Items]
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]		Secured Overnight Financing Rate (SOFR) [Member]	Secured Overnight Financing Rate (SOFR) [Member]
Warrant to purchase common stock (in shares) | shares		3,076,923
Exercise price (in dollars per share) | $ / shares		$ 1.30
Warrant exercise period		8 years
Warrant liability						$ 2,600		$ 2,600
Loss on extinguishment of debt						$ 0	$ 0	$ 517	$ 0
Forecast
Line of Credit Facility [Line Items]
Warrant to purchase common stock (in shares) | shares										1,153,846
Exercise price (in dollars per share) | $ / shares										$ 1.30
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		4.25%
Basis spread on variable rate		6.75%
Debt instrument, cap rate		15%
Debt instrument, interest rate						12.09%		12.09%
Interest expense						$ 1,600		$ 3,800
Annual interest rate, increase		3%
Late fee percentage		2%
Exit fee percentage		0.75%
Interest payable period following prepayment		12 months
Debt covenant, cash and cash equivalents		$ 15,000
Debt covenant, revenue period		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%
Prepayment fee percentage		1%
Secured Debt | Term Loan Facility | Line of Credit | Maximum
Line of Credit Facility [Line Items]
Transaction fee percentage		1.25%
Prepayment fee percentage		4%
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
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
Line of credit, maximum borrowing capacity, number of available tranches | tranche											2
Basis spread on variable rate			7.50%
Interest expense						$ 0	$ 1,600	0	$ 3,300
Extinguishment of debt		35,000
Payment of outstanding debt interest and prepayment fee		$ 200
Loss on extinguishment of debt								$ 500
Adjustment rate on variable rate			0.30%
Debt instrument, cap rate			3.35%
Term Loan | Tranche A | Keryx | Biopharma Credit Investments V (Master) LP | Collateral Agent, Pharmakon
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity											$ 80,000
Proceeds from line of credit, net					$ 77,300
Debt fees and expenses					$ 2,700
Term Loan | Tranche B | Keryx | Biopharma Credit Investments V (Master) LP | Collateral Agent, Pharmakon
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity											$ 20,000
Proceeds from line of credit, net				$ 20,000

INDEBTEDNESS - Future Principal

INDEBTEDNESS - Future Principal Payments on the Term Loans (Details) $ in Thousands	Jun. 30, 2024 USD ($)
Debt Disclosure [Abstract]
2024	$ 0
2025	0
2026	0
2027	41,363
2028	1,589
Total before unamortized discount and issuance costs	42,952
Less: unamortized discount and issuance costs	(4,921)
Total term loans	$ 38,031

DEFERRED REVENUE, REFUND LIAB_3

DEFERRED REVENUE, REFUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES - Summary of Deferred Revenue Balances (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Current portion of deferred revenue	$ 43,296	$ 0
Deferred revenue, net of current portion	0	$ 43,296
Contract with Customer, Liability, Total	43,296
Vifor (International) Ltd.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Current portion of deferred revenue	43,296
Deferred revenue, net of current portion	0
Contract with Customer, Liability, Total	$ 43,296

DEFERRED REVENUE, REFUND LIAB_4

DEFERRED REVENUE, REFUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES - Narrative (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 25, 2021 USD ($)	Feb. 28, 2022 USD ($) $ / shares shares	May 31, 2017 USD ($) $ / shares shares	Jun. 30, 2024 USD ($) shares	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) performance_obligation shares	Jun. 30, 2023 USD ($)	May 31, 2028 USD ($)	May 31, 2027 USD ($)	May 31, 2026 USD ($)	Jul. 01, 2025 USD ($)	May 03, 2024 USD ($)	Dec. 31, 2023 USD ($) shares	Mar. 18, 2022 USD ($)	Feb. 18, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue				$ 43,296		$ 43,296
Common stock, issued (in shares) | shares				209,929,145		209,929,145							194,582,539
Deferred revenue, net of current portion				$ 0		$ 0							$ 43,296
Refund liability to customer, amortization of discount				900	$ 900	1,600	$ 1,700
Refund liability to customer, amortization of deferred gain				800	1,000	1,700	2,000
Refund liability to customer				40,018		40,018							40,093
Maximum annual royalty payout capacity	$ 13,000
Percentage of royalty payment to be received once maximum annual royalty payout has been paid	85%
Maximum aggregate royalty payout capacity	$ 150,000
Liability related to sale of future royalties, net of current portion	$ 44,800			$ 53,101		$ 53,101							$ 54,013
Annual effective interest rate				0%		0%
Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sale of stock, price per share (in dollars per share) | $ / shares		$ 5
Number of shares sold in offering (in shares) | shares		4,000,000
Aggregate net proceeds from offering		$ 20,000
Vifor (International) Ltd.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue				$ 43,296		$ 43,296
Deferred revenue, net of current portion				0		0
Refund liability to customer, gross														$ 40,000
Refund liability to customer				40,000		40,000
Vifor (International) Ltd. | License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock, issued (in shares) | shares			3,571,429
Sale of stock, price per share (in dollars per share) | $ / shares			$ 14
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%
Deferred revenue															$ 25,000
Deferred revenue, net of current portion		$ 13,600	$ 4,700	43,300		$ 43,300
Number of performance obligations | performance_obligation						1
Transaction price															$ 43,300
Refund liability to customer, interest rate														15%
Vifor (International) Ltd. | License | Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, net of current portion				18,300		$ 18,300
Vifor International Limited, First Investment | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, net of current portion				4,700		4,700
Vifor International Limited, Second Investment | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, net of current portion				13,600		13,600
CSL Vifor
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Refund liability to customer, interest rate												15%
Royalty payments												$ 40,000
CSL Vifor | Forecast
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalty payments											$ 40,000
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%
CSL Vifor | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered royalty payments, percentage												14%
HealthCare Royalty Partners IV, L.P.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payments for royalties				$ 400	$ 400	$ 900	$ 1,000

DEFERRED REVENUE, REFUND LIAB_5

DEFERRED REVENUE, REFUND LIABILITY AND LIABILITY RELATED TO SALE OF FUTURE ROYALTIES - Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Feb. 25, 2021
Other Liabilities Disclosure [Abstract]
Current portion (included in accrued expenses and other current liabilities)	$ 2,013	$ 2,048
Long-term portion	53,101	54,013	$ 44,800
Total liability related to sale of future royalties	$ 55,114	$ 56,061

LEASES - Narrative (Details)

LEASES - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2023 USD ($)	Jun. 30, 2024 USD ($) ft² extension_option	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) ft² extension_option	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, remaining lease term		2 years 2 months 12 days		2 years 2 months 12 days
Operating lease, cost		$ 1,200	$ 1,400	$ 2,500	$ 3,200
Operating lease, payments		1,400	1,400	2,900	3,100
Loss on termination of lease		$ 0	524	$ 0	524
Minimum
Lessee, Lease, Description [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term		6.65%		6.65%
Maximum
Lessee, Lease, Description [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term		6.94%		6.94%
Cambridge
Lessee, Lease, Description [Line Items]
Area of property leased (in square feet) | ft²		65,167		65,167
Cambridge | Other Assets | Letter of Credit
Lessee, Lease, Description [Line Items]
Total security deposit in connection with lease		$ 1,700		$ 1,700		$ 1,700
Cambridge | Office And Storage Space
Lessee, Lease, Description [Line Items]
Leased area subject to expiration | ft²		59,216		59,216
Operating lease extensions (in extension options) | extension_option		1		1
Lease extension period		5 years		5 years
Cambridge | Laboratory Space
Lessee, Lease, Description [Line Items]
Leased area subject to expiration | ft²		5,951		5,951
Operating lease extensions (in extension options) | extension_option		1		1
Lease extension period		2 years		2 years
Boston | Office Space
Lessee, Lease, Description [Line Items]
Area of property leased (in square feet) | ft²		27,924		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 rental income		$ 0	$ 0	$ 0	$ 300

LEASES - Future Commitments und

LEASES - Future Commitments under Non-Cancelable Leases (Details) $ in Thousands	Jun. 30, 2024 USD ($)
Leases [Abstract]
Remainder of 2024	$ 2,876
2025	5,819
2026	3,613
Total lease commitments	12,308
Less: present value adjustment	(830)
Current and long-term operating lease liabilities	$ 11,478

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Millions			3 Months Ended			6 Months Ended		12 Months Ended
	Feb. 10, 2021	Mar. 11, 2020	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 22, 2022 USD ($) quarterly_payment
Commitments And Contingencies [Line Items]
Contract cost incurred in research and development activities						$ 46.7
Supply Agreement, Patheon Inc.
Commitments And Contingencies [Line Items]
Purchase commitment, option for non-auto renewal, prior written notice period		18 months
Minimum purchase commitment			$ 0			0
Siegfried Evionnaz SA
Commitments And Contingencies [Line Items]
Cost of purchased minimum quantity product			21.4			21.4
Long-term minimum purchase commitment						3.6		$ 1.5
STA Pharmaceutical Hong Kong Limited
Commitments And Contingencies [Line Items]
Long-term minimum purchase commitment						11.1
WuXi STA
Commitments And Contingencies [Line Items]
Purchase commitment, option to extend, prior notice period	18 months
Long-term purchase commitment, option to terminate, prior notice period (at least)	180 days
BioVectra Inc
Commitments And Contingencies [Line Items]
Long-term purchase commitment, termination amount payable										$ 32.5
Long-term purchase commitment, upfront payment termination amount					$ 17.5
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										$ 2.5
Long-term purchase commitment, termination amount payable after upfront payment										$ 15
Long-term purchase commitment, imputed interest on termination amount payable										17%
Long-term purchase commitment, upfront termination amount classified as cost of goods sold									$ 11.2
Amortization discount			0.4	$ 0.5		1	$ 0.9
Panion & BF Biotech, Inc | License Agreement
Commitments And Contingencies [Line Items]
Royalty payments			$ 2.5	$ 3.2		$ 4.3	$ 6

PRODUCT REVENUE AND RESERVES _3

PRODUCT REVENUE AND RESERVES FOR VARIABLE CONSIDERATION - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Total revenues	$ 43,648	$ 56,376	$ 76,255	$ 96,381
Product revenue, net
Disaggregation of Revenue [Line Items]
Total revenues	41,209	$ 42,244	72,218	$ 76,950
Accounts receivable, net	$ 27,900		$ 27,900		$ 35,900

PRODUCT REVENUE AND RESERVES _4

PRODUCT REVENUE AND RESERVES FOR VARIABLE CONSIDERATION - Product Revenue Allowance and Reserve Categories (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 31,514	$ 38,434
Current provisions related to sales in current year	25,297	46,779
Adjustments related to prior year sales	(129)	(652)
Credits/payments made	(35,183)	(52,533)
Ending balance	21,499	32,028
Chargebacks and Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	1,607	1,259
Current provisions related to sales in current year	4,054	5,215
Adjustments related to prior year sales	77	(8)
Credits/payments made	(4,301)	(5,617)
Ending balance	1,437	849
Rebates, Fees and other Deductions
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	22,991	26,252
Current provisions related to sales in current year	19,373	38,998
Adjustments related to prior year sales	(101)	(473)
Credits/payments made	(27,530)	(41,474)
Ending balance	14,733	23,303
Product Returns
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	6,916	10,923
Current provisions related to sales in current year	1,870	2,566
Adjustments related to prior year sales	(105)	(171)
Credits/payments made	(3,352)	(5,442)
Ending balance	$ 5,329	$ 7,876

LICENSE, COLLABORATION AND OT_3

LICENSE, COLLABORATION AND OTHER REVENUE - Revenues Recognized From License, Collaboration and Other Significant Agreements (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Dec. 11, 2015	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
License Collaboration And Other Revenue [Abstract]
Total revenues		$ 43,648	$ 56,376	$ 76,255	$ 96,381
MTPC
License Collaboration And Other Revenue [Abstract]
Total revenues	$ 5,900
License, collaboration and other revenue
License Collaboration And Other Revenue [Abstract]
Total revenues		2,439	14,132	4,037	19,431
License, collaboration and other revenue | Medice
License Collaboration And Other Revenue [Abstract]
Total revenues		0	10,000	0	10,000
License, collaboration and other revenue | MTPC
License Collaboration And Other Revenue [Abstract]
Total revenues		1,169	516	1,581	4,678
License, collaboration and other revenue | JT and Torii
License Collaboration And Other Revenue [Abstract]
Total revenues		1,270	1,391	2,456	2,528
License, collaboration and other revenue | Otsuka | Otsuka
License Collaboration And Other Revenue [Abstract]
Total revenues		0	2,225	0	2,225
License, collaboration and other revenue | Total license and other revenue
License Collaboration And Other Revenue [Abstract]
Total revenues		$ 2,439	$ 14,132	$ 4,037	$ 19,431

LICENSE, COLLABORATION AND OT_4

LICENSE, COLLABORATION AND OTHER REVENUE - Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Contract liability:
Balance at End of Period	$ 43,296
Accounts receivable
Contract asset:
Balance at Beginning of Period	3,333	$ 1,901
Additions	4,037	943
Deductions	(5,542)	(2,319)
Balance at End of Period	1,828	525
Prepaid expenses and other current assets
Contract asset:
Balance at Beginning of Period		781
Additions		0
Deductions		(781)
Balance at End of Period		0
Deferred revenue
Contract liability:
Balance at Beginning of Period	43,296	47,034
Additions	695	0
Deductions	(695)	(3,738)
Balance at End of Period	$ 43,296	$ 43,296

LICENSE, COLLABORATION AND OT_5

LICENSE, COLLABORATION AND OTHER REVENUE - Revenue Recognized Resulting from Changes in Contract Assets and Liabilities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenue Recognized in the Period:
Deferred revenue — beginning of the period	$ 0	$ 0	$ 0	$ 3,738,000
Revenue recognized from performance obligations satisfied in previous periods	$ 0	$ 0	$ 0	$ 0

LICENSE, COLLABORATION AND OT_6

LICENSE, COLLABORATION AND OTHER REVENUE - Medice License Agreement - Narrative (Details)		3 Months Ended		6 Months Ended
	May 24, 2023 USD ($) performance_obligation	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue		$ 43,296,000		$ 43,296,000
Other long-term assets		17,779,000		17,779,000		$ 12,423,000
Total revenues		43,648,000	$ 56,376,000	76,255,000	$ 96,381,000
Accounts receivable, net		29,765,000		29,765,000		39,290,000
Payables		10,107,000		10,107,000		14,635,000
License, collaboration and other revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues		2,439,000	14,132,000	4,037,000	19,431,000
MEDICE Arzneimittel Pütter GmbH & Co. KG | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of net product margin on sales in collaborative arrangement	70%
MEDICE Arzneimittel Pütter GmbH & Co. KG | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue	$ 10,000,000
Eligible milestone payments (up to)	$ 100,000,000
Tiered royalties, expected timing of satisfaction period	12 years
Termination of agreement by counterparty, written notice period	12 months
Termination of agreement eligible by counterparty, period after effective agreement date	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		$ 1,400,000
MEDICE Arzneimittel Pütter GmbH & Co. KG | License | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered royalties	10%
MEDICE Arzneimittel Pütter GmbH & Co. KG | License | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered royalties	30%
MEDICE Arzneimittel Pütter GmbH & Co. KG | License, collaboration and other revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues		0	$ 10,000,000	0	$ 10,000,000
MEDICE Arzneimittel Pütter GmbH & Co. KG, Side Letter | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue		0		0
Accounts receivable, net		0		0
Payables		0		0
Contract asset		$ 0		$ 0

LICENSE, COLLABORATION AND OT_7

LICENSE, COLLABORATION AND OTHER REVENUE - MTPC Collaboration Agreement - Narrative (Details)		3 Months Ended		6 Months Ended
	Dec. 11, 2015 USD ($) performance_obligation	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues		$ 43,648,000	$ 56,376,000	$ 76,255,000	$ 96,381,000
Deferred revenue		43,296,000		43,296,000
Accounts receivable, net		29,765,000		29,765,000		$ 39,290,000
Payables		10,107,000		10,107,000		$ 14,635,000
Revenue recognized		0	0	0	3,738,000
Mitsubishi Tanabe Pharma Corporation
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 5,900,000
Payables		0		0
Mitsubishi Tanabe Pharma Corporation | License Collaboration And Other Revenue, Royalties
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues		500,000	500,000	900,000	900,000
Mitsubishi Tanabe Pharma Corporation | Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue	$ 25,000,000			25,000,000
Mitsubishi Tanabe Pharma Corporation | Development And Commercialize Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of performance obligations | performance_obligation	2
Mitsubishi Tanabe Pharma Corporation | Development And Commercialize Research And License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment received	$ 20,000,000
Cost of research services	20,500,000
Milestone revenue	$ 10,000,000
Deferred revenue		0		0
Accounts receivable, net		0		0
Contract asset		500,000		500,000
Mitsubishi Tanabe Pharma Corporation | Mitsubishi Tanabe Pharma Corporation Supply Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue		0		0
Accounts receivable, net		0		0
Revenue recognized		700,000	$ 0	700,000	$ 3,700,000
Other liabilities, current		$ 0		$ 0

LICENSE, COLLABORATION AND OT_8

LICENSE, COLLABORATION AND OTHER REVENUE - JT and Torii Sublicense Agreement (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) performance_obligation	Jun. 30, 2023 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue	$ 43,648	$ 56,376	$ 76,255	$ 96,381
JT and Torii | Sublicense Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of performance obligations | performance_obligation			2
Recognized revenue	$ 1,300	$ 1,400	$ 2,500	$ 2,500

CAPITAL STOCK (Details)

CAPITAL STOCK (Details) - USD ($) $ / shares in Units, $ in Millions		6 Months Ended	12 Months Ended
	Apr. 07, 2022	Jun. 30, 2024	Dec. 31, 2023	Jun. 04, 2020
Class of Stock [Line Items]
Common stock, authorized (in shares)		350,000,000	350,000,000	175,000,000
Common stock, par value (in dollars per share)		$ 0.00001	$ 0.00001
Common stock, outstanding (in shares)		209,929,145	194,582,539
Common stock, issued (in shares)		209,929,145	194,582,539
Preferred stock, authorized (in shares)		25,000,000	25,000,000
Preferred stock, par value (in dollars per share)		$ 0.00001	$ 0.00001
Preferred stock, issued (in shares)		0	0
Preferred stock, outstanding (in shares)		0	0
Open 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
Maximum | Open Market Sale Agreement, Authorized April 2022
Class of Stock [Line Items]
Common stock sales agreement amount	$ 26

STOCK-BASED COMPENSATION AND _3

STOCK-BASED COMPENSATION AND BENEFIT PLAN - Narrative (Details)		3 Months Ended		6 Months Ended
	Jun. 06, 2019 USD ($) shares	Jun. 30, 2024 USD ($) shares	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) installment shares	Jun. 30, 2023 USD ($)	Dec. 31, 2023 shares
Class of Stock [Line Items]
Stock-based compensation expense | $		$ 2,072,000	$ 3,490,000	$ 4,432,000	$ 5,979,000
Granted (in shares)				5,037,450
Number of options outstanding (in shares)		17,278,820		17,278,820		13,312,835
Unrecognized compensation costs, options | $		$ 9,300,000		$ 9,300,000
Unrecognized compensation costs, options, period for recognition				2 years 11 months 8 days
2014 Employee Stock Purchase Plan
Class of Stock [Line Items]
Purchase price at the end of offering period	85%
Offering period	6 months
Maximum employee subscription rate	15%
Maximum employee subscription amount | $	$ 25,000
Maximum number of shares per employee in any offering period	1,500
Common stock, reserved for future issuance (in shares)		4,545,480		4,545,480		4,637,801
Number of shares issued (in shares)				92,321
Share-based Payment Arrangement, Option
Class of Stock [Line Items]
Expiration period				10 years
Share-based Payment Arrangement, Option | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage				100%
Share-based Payment Arrangement, Option | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting period				1 year
Vesting percentage				25%
Share-based Payment Arrangement, Option | Share Based Compensation Award Tranche Two
Class of Stock [Line Items]
Vesting period				1 year
Number of equal quarterly installments | installment				12
Share-based Payment Arrangement, Option | Minimum
Class of Stock [Line Items]
Vesting period				12 months
Share-based Payment Arrangement, Option | Maximum
Class of Stock [Line Items]
Vesting period				48 months
Stock appreciation rights
Class of Stock [Line Items]
Expiration period				10 years
Stock appreciation rights | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage				100%
Stock appreciation rights | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting period				1 year
Vesting percentage				25%
Stock appreciation rights | Share Based Compensation Award Tranche Two
Class of Stock [Line Items]
Vesting period				1 year
Number of equal quarterly installments | installment				12
Stock appreciation rights | Minimum
Class of Stock [Line Items]
Vesting period				12 months
Stock appreciation rights | Maximum
Class of Stock [Line Items]
Vesting period				48 months
Inducement Award Program
Class of Stock [Line Items]
Granted (in shares)				1,604,950
Number of options outstanding (in shares)		1,604,950		1,604,950
Inducement Award Program | Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Class of Stock [Line Items]
Number of options outstanding (in shares)		2,374,950		2,374,950		794,000
Unvested RSUs | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage				100%
Unvested RSUs | Share-Based Payment Arrangement, Tranche Two, Following First Anniversary After Grant Date
Class of Stock [Line Items]
Vesting period				2 years
Vesting percentage				66.67%
Number of equal quarterly installments | installment				8
Award vesting grace period				1 year
Unvested RSUs | Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting percentage				33.33%
Unvested RSUs | Share-Based Payment Arrangement, Tranche Two, Second Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting percentage				33.33%
Unvested RSUs | Share-Based Payment Arrangement, Tranche Three, Third Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting percentage				33.33%
Unvested RSUs | Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date
Class of Stock [Line Items]
Vesting percentage				33.33%
Restricted Stock Units (RSUs) And Performance Based Restricted Stock Units (PSUs)
Class of Stock [Line Items]
Unrecognized compensation costs, options, period for recognition				2 years 3 months
Unrecognized compensation costs, stock | $		$ 7,300,000		$ 7,300,000
Director | Share-based Payment Arrangement, Option | Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Class of Stock [Line Items]
Granted (in shares)				3,432,500

STOCK-BASED COMPENSATION AND _4

STOCK-BASED COMPENSATION AND BENEFIT PLAN - Equity Plans (Details) - shares	Jun. 30, 2024	Dec. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	17,278,820	13,312,835
Inducement Award Program
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	1,604,950
Keryx Equity Plans
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	208,986	232,203
Additional awards authorized for grant (in shares)	0	0
Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (the 2014 Plan) (replaces 2008 Plan)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	12,597,753	15,311,501
Additional awards authorized for grant (in shares)	0	0
Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (the 2014 Plan) (replaces 2008 Plan) | Inducement Award Program
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	1,496,428	1,616,019
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	10,435,850	1,712,400
Additional awards authorized for grant (in shares)	0	17,382,722
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan) | Inducement Award Program
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	2,374,950	794,000

STOCK-BASED COMPENSATION AND _5

STOCK-BASED COMPENSATION AND BENEFIT PLAN - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares
Stock Options
Outstanding beginning balance (in shares) | shares	13,312,835
Granted (in shares) | shares	5,037,450
Exercised (in shares) | shares	(304,152)
Expired (in shares) | shares	(119,043)
Canceled and forfeited (in shares) | shares	(648,270)
Outstanding ending balance (in shares) | shares	17,278,820	13,312,835
Options exercisable at end of period (in shares) | shares	8,559,257
Weighted Average Exercise Price
Outstanding beginning balance (in dollars per share) | $ / shares	$ 4.20
Granted (in dollars per share) | $ / shares	1.57
Exercised (in dollars per share) | $ / shares	0.51
Expired (in dollars per share) | $ / shares	21.02
Canceled and forfeited (in dollars per share) | $ / shares	3.11
Outstanding ending balance (in dollars per share) | $ / shares	3.42	$ 4.20
Options exercisable at end of period, weighted-average exercise price (in dollars per share) | $ / shares	$ 5.40
Weighted-Average Contractual Life (years)
Options outstanding, weighted-average remaining contractual life (in years)	7 years 4 months 13 days	7 years 3 months 7 days
Options exercisable at end of period, weighted-average remaining contractual life (in years)	5 years 7 months 2 days
Options outstanding, aggregate intrinsic value | $	$ 1,521	$ 0

STOCK-BASED COMPENSATION AND _6

STOCK-BASED COMPENSATION AND BENEFIT PLAN - RSU and PSU Activity (Details) - Restricted Stock Units (RSUs) And Performance Based Restricted Stock Units (PSUs)	6 Months Ended
	Jun. 30, 2024 $ / shares shares
2014 Stock Incentive Plan
Number of Shares
Outstanding beginning balance (in shares) | shares	3,339,869
Granted (in shares) | shares	0
Vested (in shares) | shares	(1,478,822)
Forfeited and canceled (in shares) | shares	(210,678)
Outstanding ending balance (in shares) | shares	1,650,369
Weighted Average Fair Value
Outstanding beginning balance, weighted average fair value (in dollars per share) | $ / shares	$ 1.30
Granted, weighted average fair value (in dollars per share) | $ / shares	0
Vested, weighted-average grant date fair value (in dollars per share) | $ / shares	1.62
Forfeited and canceled, weighted average fair value (in dollars per share) | $ / shares	0.90
Outstanding ending balance, weighted average fair value (in dollars per share) | $ / shares	$ 1.07
2023 Stock Incentive Plan
Number of Shares
Outstanding beginning balance (in shares) | shares	603,400
Granted (in shares) | shares	3,968,200
Vested (in shares) | shares	(210,000)
Forfeited and canceled (in shares) | shares	(48,200)
Outstanding ending balance (in shares) | shares	4,313,400
Weighted Average Fair Value
Outstanding beginning balance, weighted average fair value (in dollars per share) | $ / shares	$ 1.48
Granted, weighted average fair value (in dollars per share) | $ / shares	1.59
Vested, weighted-average grant date fair value (in dollars per share) | $ / shares	1.20
Forfeited and canceled, weighted average fair value (in dollars per share) | $ / shares	1.68
Outstanding ending balance, weighted average fair value (in dollars per share) | $ / shares	$ 1.59

STOCK-BASED COMPENSATION AND _7

STOCK-BASED COMPENSATION AND BENEFIT PLAN - Assumptions Used in Black-Scholes Option Pricing Model (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk-free interest rate, minimum	4.24%	3.67%	3.90%	3.54%
Risk-free interest rate, maximum	4.66%	3.99%	4.66%	3.99%
Expected volatility, minimum	109.98%	102.31%	109.98%	100.97%
Expected volatility, maximum	118.61%	111.71%	118.61%	111.71%
Expected dividend yield	0%	0%	0%	0%
Fair value at grant date (in dollars per share)	$ 0.91	$ 0.97	$ 1.35	$ 0.56
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	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	6 years 3 months

STOCK-BASED COMPENSATION AND _8

STOCK-BASED COMPENSATION AND BENEFIT PLAN - Stock-Based Compensation Expense in Consolidated Statement of Operations and Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 2,072	$ 3,490	$ 4,432	$ 5,979
Cost of goods sold
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	83	73	169	139
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	396	532	815	1,202
Selling, general and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	1,593	2,685	3,410	4,220
Restructuring
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 0	$ 200	$ 38	$ 418

NET LOSS PER SHARE (Details)

NET LOSS PER SHARE (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 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)	26,319,512	18,350,049	26,319,512	18,350,049
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)	3,076,923	0	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)	16,643,507	13,118,185	16,643,507	13,118,185
Unvested RSUs
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)	5,963,769	4,596,551	5,963,769	4,596,551
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	635,313
Contingently Issuable 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)			1,153,846

Subsequent Events (Details)

Subsequent Events (Details) - CSL Vifor - USD ($) $ in Millions	Jul. 10, 2024	May 03, 2024
Subsequent Event [Line Items]
Royalty payments		$ 40
Subsequent Event
Subsequent Event [Line Items]
Royalty payments	$ 40
Tiered royalty payments as a percentage of net sales	$ 450