Spyre Therapeutics (SYRE) 10-Q 7 Aug 24 2024 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2024	Aug. 01, 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	001-37722
Entity Registrant Name	SPYRE THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-4312787
Entity Address, Address Line One	221 Crescent Street
Entity Address, Address Line Two	Building 23
Entity Address, Address Line Three	Suite 105
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02453
City Area Code	617
Local Phone Number	651-5940
Title of 12(b) Security	Common Stock, $0.0001 Par Value Per Share
Trading Symbol	SYRE
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		50,792,374
Entity Central Index Key	0001636282
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
CURRENT ASSETS
Cash and cash equivalents	$ 45,144	$ 188,893
Marketable securities	380,851	150,384
Prepaid expenses and other current assets	9,741	2,251
Total current assets	435,736	341,528
Restricted cash	321	322
Other non-current assets	10	9
TOTAL ASSETS	436,067	341,859
CURRENT LIABILITIES
Accounts payable	3,231	896
CVR liability	2,640	1,390
Accrued and other current liabilities	5,683	13,108
Total current liabilities	22,122	31,978
Non-current CVR liability	39,560	41,310
TOTAL LIABILITIES	61,682	73,288
Commitments and Contingencies (Note 7 and 8)
STOCKHOLDERS’ EQUITY
Common stock, $0.0001 par value; 400,000,000 shares authorized as of June 30, 2024 and December 31, 2023; 50,783,384 shares and 36,057,109 shares issued and outstanding as of June 30, 2024 and December 31, 2023, respectively.	12	10
Additional paid-in capital	1,066,214	763,191
Accumulated other comprehensive (loss) income	(553)	302
Accumulated deficit	(847,108)	(764,414)
TOTAL STOCKHOLDERS’ EQUITY	374,385	184,016
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY	436,067	341,859
Series B Non Voting Convertible Preferred Stock
CURRENT LIABILITIES
Series B non-voting convertible preferred stock, $0.0001 par value; 150,000 shares authorized, issued, and outstanding as of December 31, 2023.	0	84,555
STOCKHOLDERS’ EQUITY
Series A non-voting convertible preferred stock & preferred stock shares authorized, issued, and outstanding, value	$ 9,395	0
Preferred stock, authorized (in shares)	271,625
Preferred stock, issued (in shares)	16,667
Preferred stock, outstanding (in shares)	16,667
Series A Non Voting Convertible Preferred Stock
STOCKHOLDERS’ EQUITY
Series A non-voting convertible preferred stock & preferred stock shares authorized, issued, and outstanding, value	$ 146,425	$ 184,927
Preferred stock, authorized (in shares)	1,086,341	1,086,341
Preferred stock, issued (in shares)	346,045	437,037
Preferred stock, outstanding (in shares)	346,045	437,037
Preferred Stock, Excluding Series A Non Voting Convertible Preferred Stock
STOCKHOLDERS’ EQUITY
Series A non-voting convertible preferred stock & preferred stock shares authorized, issued, and outstanding, value	$ 0	$ 0
Preferred stock, authorized (in shares)	8,642,034	8,763,659
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Related Party
CURRENT LIABILITIES
Related party accounts payable and other current liabilities	$ 10,568	$ 16,584

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2024	Dec. 31, 2023
Stockholders' Equity, Number of Shares, Par Value and Other Disclosure [Abstract]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized (in shares)	400,000,000	400,000,000
Common stock, issued (in shares)	50,783,384	36,057,109
Common stock, outstanding (in shares)	50,783,384	36,057,109
Series B Non Voting Convertible Preferred Stock
Temporary Equity [Abstract]
Series B non-voting convertible preferred stock, par value (in dollars per share)		$ 0.0001
Series B non-voting convertible preferred stock, authorized (in shares)		150,000
Series B non-voting convertible preferred stock, issued (in shares)		150,000
Series B non-voting convertible preferred stock, outstanding (in shares)		150,000
Stockholders' Equity, Number of Shares, Par Value and Other Disclosure [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001
Preferred stock, authorized (in shares)	271,625
Preferred stock, issued (in shares)	16,667
Preferred stock, outstanding (in shares)	16,667
Series A Non Voting Convertible Preferred Stock
Stockholders' Equity, Number of Shares, Par Value and Other Disclosure [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, authorized (in shares)	1,086,341	1,086,341
Preferred stock, issued (in shares)	346,045	437,037
Preferred stock, outstanding (in shares)	346,045	437,037
Preferred Stock, Excluding Series A Non Voting Convertible Preferred Stock
Stockholders' Equity, Number of Shares, Par Value and Other Disclosure [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, authorized (in shares)	8,642,034	8,763,659
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenue:
Total revenue		$ 0	$ 688	$ 0	$ 886
Operating expenses:
Research and development	[1]	32,636	17,386	67,564	31,162
General and administrative		11,511	12,062	24,357	17,290
Acquired in-process research and development		0	130,486	0	130,486
Total operating expenses		44,147	159,934	91,921	178,938
Loss from operations		(44,147)	(159,246)	(91,921)	(178,052)
Other income (expense):
Interest income		5,920	350	10,352	770
Other expense, net		(610)	(8)	(1,093)	(80)
Total other income (expense)		5,310	(57,828)	9,259	(57,480)
Loss before income tax expense		(38,837)	(217,074)	(82,662)	(235,532)
Income tax (expense) benefit		0	(7)	(32)	29
Net loss		$ (38,837)	$ (217,081)	$ (82,694)	$ (235,503)
Net loss per share, basic (in dollars per share)		$ (0.86)	$ (56.79)	$ (2.02)	$ (62.03)
Net loss per share, diluted (in dollars per share)		$ (0.86)	$ (56.79)	$ (2.02)	$ (62.03)
Weighted-average common shares outstanding, basic (in shares)		45,316,264	3,822,605	40,914,463	3,796,699
Weighted-average common shares outstanding, diluted (in shares)		45,316,264	3,822,605	40,914,463	3,796,699
Forward contract liability
Other income (expense):
Change in fair value of forward contract liability		$ 0	$ (58,170)	$ 0	$ (58,170)
Development fee and royalty
Revenue:
Total revenue		$ 0	$ 688	$ 0	$ 886
[1] Includes $9.4 million and $26.5 million in related party expenses for the three and six months ended June 30, 2024, respectively, and $1.4 million related party expenses for the three and six months ended June 30, 2023.

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Research and development	[1]	$ 32,636	$ 17,386	$ 67,564	$ 31,162
Related Party
Research and development		$ 9,400	$ 1,400	$ 26,500	$ 1,400
[1] Includes $9.4 million and $26.5 million in related party expenses for the three and six months ended June 30, 2024, respectively, and $1.4 million related party expenses for the three and six months ended June 30, 2023.

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (38,837)	$ (217,081)	$ (82,694)	$ (235,503)
Other comprehensive income (loss):
Foreign currency translation adjustment	4	18	20	28
Unrealized (loss) gain on marketable securities	(194)	(1)	(875)	31
Total comprehensive loss	$ (39,027)	$ (217,064)	$ (83,549)	$ (235,444)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Non Voting Convertible Preferred Stock	Series B Non Voting Convertible Preferred Stock	Preferred Stock Series A Non Voting Convertible Preferred Stock	Preferred Stock Series B Non Voting Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2022				0
Beginning balance at Dec. 31, 2022				$ 0
Ending balance (in shares) at Mar. 31, 2023				0
Ending balance at Mar. 31, 2023				$ 0
Beginning balance, common stock (in shares) at Dec. 31, 2022						2,614,000
Beginning balance at Dec. 31, 2022	$ 50,305					$ 6	$ 475,971	$ (48)	$ (425,624)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with employee stock purchase plan (in shares)						2,000
Issuance of common stock in connection with employee stock purchase plan	18						18
Stock-based compensation expense	1,709						1,709
Foreign currency translation adjustment	10							10
Unrealized gain (loss) on marketable securities	32							32
Net loss	(18,422)								(18,422)
Ending balance, common stock (in shares) at Mar. 31, 2023						2,616,000
Ending balance at Mar. 31, 2023	33,652					$ 6	477,698	(6)	(444,046)
Beginning balance (in shares) at Dec. 31, 2022				0
Beginning balance at Dec. 31, 2022				$ 0
Ending balance (in shares) at Jun. 30, 2023				721,000
Ending balance at Jun. 30, 2023				$ 197,323
Beginning balance, common stock (in shares) at Dec. 31, 2022						2,614,000
Beginning balance at Dec. 31, 2022	50,305					$ 6	475,971	(48)	(425,624)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	28
Unrealized gain (loss) on marketable securities	31
Net loss	(235,503)
Ending balance, common stock (in shares) at Jun. 30, 2023						3,240,000
Ending balance at Jun. 30, 2023	(207,369)					$ 6	453,741	11	(661,127)
Beginning balance (in shares) at Mar. 31, 2023				0
Beginning balance at Mar. 31, 2023				$ 0
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A/B non-voting convertible preferred stock in connection with private placement, net of financing costs (in shares)				721,000
Issuance of Series A/B non-voting convertible preferred stock in connection with private placement, net of financing costs				$ 197,323
Ending balance (in shares) at Jun. 30, 2023				721,000
Ending balance at Jun. 30, 2023				$ 197,323
Beginning balance, common stock (in shares) at Mar. 31, 2023						2,616,000
Beginning balance at Mar. 31, 2023	33,652					$ 6	477,698	(6)	(444,046)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock forward in connection with the asset acquisition of Spyre	3,768						3,768
Issuance of common stock in connection with exercise of pre-funded warrants (in shares)						624,000
CVR distribution to common stockholders	(29,500)						(29,500)
Stock-based compensation expense	1,775						1,775
Foreign currency translation adjustment	18							18
Unrealized gain (loss) on marketable securities	(1)							(1)
Net loss	(217,081)								(217,081)
Ending balance, common stock (in shares) at Jun. 30, 2023						3,240,000
Ending balance at Jun. 30, 2023	(207,369)					$ 6	453,741	11	(661,127)
Beginning balance (in shares) at Dec. 31, 2023			150,000		150,000
Beginning balance at Dec. 31, 2023			$ 84,555		$ 84,555
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A/B non-voting convertible preferred stock in connection with private placement, net of financing costs (in shares)					122,000
Issuance of Series A/B non-voting convertible preferred stock in connection with private placement, net of financing costs					$ 168,850
Ending balance (in shares) at Mar. 31, 2024					272,000
Ending balance at Mar. 31, 2024					$ 253,405
Beginning balance, preferred stock (in shares) at Dec. 31, 2023		437,037		437,000	0
Beginning balance, common stock (in shares) at Dec. 31, 2023						36,057,000
Beginning balance at Dec. 31, 2023	184,016			$ 184,927	$ 0	$ 10	763,191	302	(764,414)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with exercise of stock options and employee stock purchase plan (in shares)						572,000
Issuance of common stock in connection with exercise of stock options and employee stock purchase plan	4,390						4,390
Stock-based compensation expense	8,385						8,385
Foreign currency translation adjustment	16							16
Unrealized gain (loss) on marketable securities	(681)							(681)
Net loss	(43,857)								(43,857)
Ending balance, preferred stock (in shares) at Mar. 31, 2024				437,000	0
Ending balance, common stock (in shares) at Mar. 31, 2024						36,629,000
Ending balance at Mar. 31, 2024	152,269			$ 184,927	$ 0	$ 10	775,966	(363)	(808,271)
Beginning balance (in shares) at Dec. 31, 2023			150,000		150,000
Beginning balance at Dec. 31, 2023			$ 84,555		$ 84,555
Ending balance (in shares) at Jun. 30, 2024					0
Ending balance at Jun. 30, 2024			$ 0		$ 0
Beginning balance, preferred stock (in shares) at Dec. 31, 2023		437,037		437,000	0
Beginning balance, common stock (in shares) at Dec. 31, 2023						36,057,000
Beginning balance at Dec. 31, 2023	184,016			$ 184,927	$ 0	$ 10	763,191	302	(764,414)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment	20
Unrealized gain (loss) on marketable securities	(875)
Net loss	(82,694)
Ending balance, preferred stock (in shares) at Jun. 30, 2024		346,045	16,667	346,000	17,000
Ending balance, common stock (in shares) at Jun. 30, 2024						50,783,000
Ending balance at Jun. 30, 2024	374,385			$ 146,425	$ 9,395	$ 12	1,066,214	(553)	(847,108)
Beginning balance (in shares) at Mar. 31, 2024					272,000
Beginning balance at Mar. 31, 2024					$ 253,405
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of Series B non-voting convertible preferred stock into common stock (in shares)					(272,000)
Stockholder approval of the issuance of Common Stock upon conversion of Series B convertible non-voting preferred stock					$ (253,405)
Ending balance (in shares) at Jun. 30, 2024					0
Ending balance at Jun. 30, 2024			$ 0		$ 0
Beginning balance, preferred stock (in shares) at Mar. 31, 2024				437,000	0
Beginning balance, common stock (in shares) at Mar. 31, 2024						36,629,000
Beginning balance at Mar. 31, 2024	152,269			$ 184,927	$ 0	$ 10	775,966	(363)	(808,271)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholder approval of conversion of Series B Convertible Non-Voting Preferred Stock to Common Stock (in shares)					272,000
Stockholder approval of the issuance of Common Stock upon conversion of Series B convertible non-voting preferred stock	253,405				$ 253,405
Issuance of common stock in connection with exercise of stock options and employee stock purchase plan (in shares)						66,000
Issuance of common stock in connection with exercise of stock options and employee stock purchase plan	494						494
Conversion of Series B non-voting convertible preferred stock into common stock (in shares)					(255,000)	10,198,000
Conversion of Series B non-voting convertible preferred stock into common stock	0				$ (244,010)	$ 1	244,009
Exchange of Series A non-voting convertible preferred stock into common stock (in shares)				(91,000)		3,640,000
Exchange of Series A non-voting convertible preferred stock for common stock	0			$ (38,502)		$ 1	38,501
Issuance of common stock in connection with exercise of pre-funded warrants (in shares)						250,000
Issuance of common stock in connection with exercise of pre-funded warrants	1						1
Stock-based compensation expense	7,243						7,243
Foreign currency translation adjustment	4							4
Unrealized gain (loss) on marketable securities	(194)							(194)
Net loss	(38,837)								(38,837)
Ending balance, preferred stock (in shares) at Jun. 30, 2024		346,045	16,667	346,000	17,000
Ending balance, common stock (in shares) at Jun. 30, 2024						50,783,000
Ending balance at Jun. 30, 2024	$ 374,385			$ 146,425	$ 9,395	$ 12	$ 1,066,214	$ (553)	$ (847,108)

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (82,694)	$ (235,503)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	22,517	3,620
Acquired in-process research and development	0	130,486
Lease ROU asset and leasehold improvement impairment loss	0	2,580
Loss on disposal of long-lived assets	0	915
Net accretion of discount on marketable securities	(5,984)	(123)
Interest proceeds from maturities of zero coupon US Treasury Bills	124	0
Depreciation and amortization	0	744
Amortization of operating lease assets	0	220
Other	0	6
Changes in operating assets and liabilities:
Accounts payable	2,335	2,045
Accrued and other liabilities	(7,623)	(1,058)
Related party accounts payable	(12,906)	1,247
Prepaid expenses and other assets	(7,489)	3,368
Deferred revenue	0	575
Development receivables	0	(1,271)
Operating lease liabilities	0	(298)
Net cash used in operating activities	(90,790)	(34,277)
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from maturities and sales of marketable securities	105,626	21,000
Purchases of marketable securities	(331,107)	0
Cash assumed from asset acquisition of Spyre	0	3,035
Proceeds from sale of property and equipment	0	475
Net cash (used in) and provided by investing activities	(225,481)	24,510
CASH FLOWS FROM FINANCING ACTIVITIES
Payments related to contingent value rights liability	(1,430)	0
Proceeds from employee stock option exercises, employee stock plan purchases, and exercise of prefunded warrants	4,885	18
Principal payments on finance lease obligation	0	(16)
Net cash provided by financing activities	172,525	210,002
Effect of exchange rate on cash, cash equivalents, and restricted cash	(4)	24
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(143,750)	200,259
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	189,215	36,416
End of period	45,465	236,675
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Exchange of Series A non-voting convertible preferred stock for common stock	38,502	0
Conversion of Series B non-voting convertible preferred stock into common stock	244,010	0
Unpaid direct transaction costs related to the asset acquisition of Spyre	0	2,067
Reconciliation of Cash, Cash Equivalents, and Restricted Cash Reported in the Statement of Financial Position
Cash and cash equivalents	45,144	235,358
Restricted cash	321	1,317
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	45,465	236,675
Series B Non Voting Convertible Preferred Stock
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of Series A/B non-voting convertible preferred stock in connection with private placement	169,070	0
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Unpaid amounts related to issuance of Series B non-voting convertible preferred stock in connection with private placement	220	0
Series A Non Voting Convertible Preferred Stock
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of Series A/B non-voting convertible preferred stock in connection with private placement	0	210,000
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Unpaid amounts related to issuance of Series A non-voting convertible preferred stock in connection with private placement	0	12,677
CVR liability
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of derivative liability	930	0
Forward contract liability
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of derivative liability	$ 0	$ 58,170

The Company and Basis of Presen

The Company and Basis of Presentation	6 Months Ended
	Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company and Basis of Presentation	The Company and Basis of Presentation Spyre Therapeutics, Inc., formerly Aeglea BioTherapeutics, Inc. (“Spyre” or the “Company”), is a clinical stage biotechnology company focused on developing next generation therapeutics for patients living with inflammatory bowel disease. The Company was formed as a Limited Liability Company ("LLC") in Delaware on December 16, 2013 under the name Aeglea BioTherapeutics Holdings, LLC and was converted from a Delaware LLC to a Delaware corporation on March 10, 2015. On November 27, 2023, the Company completed its corporate rebranding, changing the name of the Company to Spyre Therapeutics, Inc. The Company operates in one segment and has its principal offices in Waltham, Massachusetts. On September 8, 2023, the Company effected a reverse stock split of its Common Stock at a ratio of 1-for-25 (the “Reverse Split”). Except as indicated otherwise, all share numbers related to the Company's Common Stock disclosed in these financial statements have been adjusted on a post-Reverse Split basis. On April 12, 2023, based on the review of the inconclusive interim results from the Company's Phase 1/2 clinical trial of pegtarviliase for the treatment of Classical Homocystinuria and other business considerations, the Company announced that it had initiated a process to explore strategic alternatives to maximize stockholder value and engaged an independent exclusive financial advisor to support this process. As a result, in April 2023, the Company implemented a restructuring plan resulting in an approximate 83% reduction of the Company’s existing headcount. On June 22, 2023, the Company acquired, in accordance with the terms of the Agreement and Plan of Merger (the "Acquisition Agreement"), the assets of Spyre Therapeutics, Inc. (“Pre-Merger Spyre”), a privately held biotechnology company advancing a pipeline of antibody therapeutics with the potential to transform the treatment of inflammatory bowel disease through a research and development option agreement ("Paragon Agreement") with Paragon Therapeutics, Inc. ("Paragon"). The asset acquisition was accomplished through a two-step reverse triangular merger whereby a wholly owned subsidiary of the Company merged with and into Pre-Merger Spyre, which existed at the time the Acquisition Agreement was entered into, and became a wholly owned subsidiary of the Company in accordance with the terms of the Acquisition Agreement. Immediately following this merger, Pre-Merger Spyre merged with and into a second wholly owned subsidiary of the Company (“Merger Sub”) in accordance with the terms of the Acquisition Agreement and Pre-Merger Spyre ceased to exist. Subsequently, Aeglea BioTherapeutics, Inc. was renamed Spyre Therapeutics, Inc. and is a different entity than Pre-Merger Spyre, which ceased to exist upon merging with Merger Sub. The transaction was structured as a stock-for-stock transaction pursuant to which all of Pre-Merger Spyre's outstanding equity interests were exchanged based on a fixed exchange ratio of 0.5494488 to 1 for consideration from the Company of 517,809 shares of common stock, par value of $0.0001 per share ("Common Stock"), and 364,887 shares of Series A non-voting convertible preferred stock, par value of $0.0001 per share ("Series A Preferred Stock") (convertible on a 40 to 1 basis), in addition to the assumption of outstanding and unexercised stock options to purchase 2,734 shares of Common Stock from the Amended and Restated Spyre 2023 Equity Incentive Plan (the "Asset Acquisition"). The Common Stock and Series A Preferred Stock related to the Asset Acquisition were issued to the Pre-Merger Spyre stockholders on July 7, 2023. In connection with the Asset Acquisition, on June 26, 2023, the Company completed a private placement of shares of Series A Preferred Stock (the “June 2023 PIPE”) to a group of investors (the “June 2023 Investors”). The Company sold an aggregate of 721,452 shares of Series A Preferred Stock for an aggregate purchase price of approximately $210.0 million before deducting approximately $12.7 million in placement agent and other offering expenses (together with the Asset Acquisition, the “Transactions”). In connection with the Asset Acquisition, a non-transferable contingent value right ("CVR") was distributed to stockholders of record of the Company as of the close of business on July 3, 2023 (the "Legacy Stockholders"), but was not distributed to the holders of shares of Common Stock or Series A Preferred Stock issued to the former stockholders of Pre-Merger Spyre or the June 2023 Investors in the Transactions. Holders of the CVRs will be entitled to receive cash payments from proceeds received by the Company for a three-year period related to the disposition or monetization of its legacy assets for a period of one-year following the closing of the Asset Acquisition. On November 21, 2023, the Company's stockholders approved the issuance of Common Stock upon conversion of the Company's Series A Preferred Stock to Common Stock. A total of 649,302 shares of Series A Preferred Stock automatically converted to 25,972,080 shares of Common Stock; 437,037 shares of Series A Preferred Stock did not automatically convert and remained outstanding after the conversion. On December 11, 2023, the Company completed a private placement of shares of Common Stock and Series B non-voting convertible preferred stock, par value of $0.0001 per share ("Series B Preferred Stock") (convertible on a 40 to 1 basis) (the “December 2023 PIPE”) to a group of investors. The Company sold an aggregate of 6,000,000 shares of Common Stock and 150,000 shares of Series B Preferred Stock for an aggregate purchase price of approximately $180.0 million before deducting approximately $10.9 million of placement agent and other offering expenses. On March 20, 2024, the Company completed a private placement of Series B Preferred Stock (convertible on a 40 to 1 basis) (the “March 2024 PIPE”) to a group of investors. The Company sold 121,625 shares of Series B Preferred Stock for a purchase price of $180.0 million before deducting approximately $11.2 million of placement agent and other offering costs. On April 23, 2024, the Company entered into an exchange agreement with Fairmount Healthcare Fund II L.P. (the “Stockholder”), pursuant to which the Stockholder agreed to exchange an aggregate of 90,992 shares of Series A Preferred Stock for an aggregate of 3,639,680 shares of Common Stock (the “April 2024 Exchange”). The Common Stock issued in connection with the April 2024 Exchange was issued without registration under the Securities Act of 1933, as amended (the “Securities Act”) in reliance on the exemption from registration contained in Section 3(a)(9) of the Securities Act. The April 2024 Exchange closed on April 25, 2024, with 346,045 shares of Series A Preferred Stock remaining outstanding following the April 2024 Exchange. On May 14, 2024, the Company's stockholders approved the issuance of Common Stock upon conversion of the Company's Series B Preferred Stock to Common Stock. A total of 254,958 shares of Series B Preferred Stock automatically converted to 10,198,320 shares of Common Stock; 16,667 shares of Series B Preferred Stock did not automatically convert and remained outstanding as of June 30, 2024. Liquidity The Company is a clinical stage biotechnology company with a limited operating history, and due to its significant research and development expenditures, the Company has generated operating losses since its inception and has not generated any revenue from the commercial sale of any products. There can be no assurance that profitable operations will ever be achieved, and, if achieved, whether profitability can be sustained on a continuing basis. Since its inception and through June 30, 2024, the Company has funded our operations by raising an aggregate of approximately $1.1 billion of gross proceeds from the sale and issuance of convertible preferred stock and common stock, pre-funded warrants, the collection of grant proceeds, and the licensing of its product rights for commercialization of pegzilarginase in Europe and certain countries in the Middle East. As of June 30, 2024, Spyre had an accumulated deficit of $847.1 million, and cash, cash equivalents, marketable securities and restricted cash of $426.3 million. Based on current operating plans, the Company has sufficient resources to fund operations for at least one year from the issuance date of these financial statements with existing cash, cash equivalents, and marketable securities. Spyre will need to secure additional financing in the future to fund additional research and development, and before a commercial drug can be produced, marketed and sold. If the Company is unable to obtain additional financing or generate license or product revenue, the lack of liquidity could have a material adverse effect on the Company. Basis of Presentation The consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States (“U.S. GAAP”) as defined by the Financial Accounting Standards Board and include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Reclassification of Prior Year Presentation Certain prior year amounts have been reclassified for consistency with the current year presentation. These reclassifications had no effect on the reported results of operations or balance sheets. Unaudited Interim Financial Information The interim condensed consolidated financial statements included in this Quarterly Report on Form 10-Q are unaudited. The unaudited interim financial statements have been prepared on the same basis as the annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for a fair statement of the Company’s financial position as of June 30, 2024, and its results of operations for the three and six months ended June 30, 2024 and 2023, changes in convertible preferred stock and stockholders’ equity for the three and six months ended June 30, 2024 and 2023, and cash flows for the six months ended June 30, 2024 and 2023. The results of operations for the three and six months ended June 30, 2024, are not necessarily indicative of the results to be expected for the year ending December 31, 2024 or for any other future annual or interim period. The December 31, 2023 balance sheet was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP for complete financial statements. These financial statements should be read in conjunction with the audited financial statements included in the Company’s Form 10-K for the year ended December 31, 2023 (the "Annual Report") as filed with the SEC on February 29, 2024 and amended on March 1, 2024.

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 These interim condensed consolidated financial statements have been prepared in accordance with U.S. GAAP and SEC instructions for interim financial information, and should be read in conjunction with the Company's Annual Report. Significant accounting policies and other disclosures normally provided have been omitted since such items are disclosed in the Company's Annual Report. The Company uses the same accounting policies in preparing quarterly and annual financial statements. Other than policies noted below, there have been no significant changes from the significant accounting policies and estimates disclosed in the Notes titled “1. The Company and Basis of Presentation” and "2. Summary of Significant Accounting Policies” of the Company's Annual Report. License Agreements Contingent Milestone Payments The Company’s license agreements include specific development, regulatory, and clinical milestone payments that are payable upon the resolution of a contingency, such as upon the selection of a development candidate, first dosing of a human patient in clinical trials or receipt of the Food Drug and Administration’s (“FDA”) approval of a Spyre drug. The achievement of these milestone payments involves many factors outside of the Company’s control and therefore the associated likelihood cannot be considered probable until the related contingency is resolved. Based on the preceding, the Company accrues each milestone payment upon the achievement of the applicable milestone event. Recently Adopted Accounting Pronouncement There have been no recent accounting pronouncements or changes in accounting pronouncements during the six months ended June 30, 2024 that are of significance or potential significance to the Company.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The following tables set forth the fair value of the Company’s financial assets and liabilities at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands): June 30, 2024 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 43,377 $ — $ — $ 43,377 U.S. government treasury securities 136,857 — — 136,857 U.S. government agency securities — 92,566 — 92,566 Commercial paper — 119,716 — 119,716 Corporate bonds — 31,712 — 31,712 Total financial assets $ 180,234 $ 243,994 $ — $ 424,228 Liabilities: Parapyre Option Obligation $ — $ 6,889 $ — $ 6,889 CVR liability — — 42,200 42,200 Total liabilities $ — $ 6,889 $ 42,200 $ 49,089 December 31, 2023 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 150,648 $ — $ — $ 150,648 U.S. government treasury securities 32,843 — — 32,843 U.S. government agency securities — 16,257 — 16,257 Commercial paper — 104,141 — 104,141 Corporate bonds — 33,064 — 33,064 Total financial assets $ 183,491 $ 153,462 $ — $ 336,953 Liabilities: CVR liability $ — $ — $ 42,700 $ 42,700 Total liabilities $ — $ — $ 42,700 $ 42,700 The Company measures the fair value of money market funds and U.S. government treasury securities on quoted prices in active markets for identical assets or liabilities. The Level 2 assets include U.S. government agency securities, commercial paper and corporate bonds, and are valued based on quoted prices for similar assets in active markets and inputs other than quoted prices that are derived from observable market data. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers between Level 1, Level 2, or Level 3 during the periods presented. Parapyre Option Obligation Under the Paragon Agreement, the Company is obligated to issue Parapyre Holding LLC ("Parapyre") an annual equity grant of warrants, on the last business day of each of the years ended December 31, 2023 and December 31, 2024, to purchase 1% of the then outstanding shares of the Company’s Common Stock, on a fully diluted basis, during the term of the Paragon Agreement (the "Parapyre Option Obligation"). The Company determined that the 2023 and 2024 grants are two separate grants, as there would be no obligation for the 2024 grant had the Company exercised or terminated all of the options under the Paragon Agreement prior to December 31, 2023. The service inception period for the grant precedes the grant date, with the full award being vested as of the grant date with no post-grant date service requirement. Accordingly, a liability related to the Parapyre Option Obligation is recorded pursuant to the Paragon Agreement during interim periods. On December 31, 2023, the Company settled its 2023 obligation under the Parapyre Option Obligation by issuing Parapyre 684,407 warrants to purchase the Company's Common Stock, with a $21.52 per share exercise price for each warrant. The Parapyre Option Obligation is considered a Level 2 liability based on observable market data for substantially the full term of the liability. The Parapyre Option Obligation is measured each period using a Black-Scholes model to estimate the fair value of the option grant. Changes in the fair value of the Parapyre Option Obligation are recorded as stock-based compensation within Research and development expenses for non-employees who provided pre-clinical development services. CVR Liability In connection with the Asset Acquisition, a non-transferable CVR was distributed to the Legacy Stockholders, but was not distributed to holders of shares of Common Stock or Series A Preferred Stock issued to the June 2023 Investors or former stockholders of Pre-Merger Spyre in connection with the Transactions. Holders of the CVR will be entitled to receive certain cash payments from proceeds received by the Company for a three-year period, if any, related to the disposition or monetization of the Company’s legacy assets for a period of one year following the closing of the Asset Acquisition. The fair value of the CVR liability was determined using the probability weighted discounted cash flow method to estimate future cash flows associated with the sale of the legacy assets. Analogous to a dividend being declared/approved in one period and paid out in another, the liability was recorded at the date of approval, June 22, 2023, as a Common Stock dividend, returning capital to the Legacy Stockholders. Changes in fair value of the liability will be recognized as a component of Other income (expense) in the consolidated statement of operations and comprehensive loss in each reporting period. The liability value is based on significant inputs not observable in the market such as estimated cash flows, estimated probabilities of regulatory success, and discount rates, which represent a Level 3 measurement within the fair value hierarchy. The significant inputs used to estimate the fair value of the CVR liability were as follows: June 30, 2024 Estimated cash flow dates 02/15/25 - 06/22/26 Estimated probability of success 39% - 100% Estimated reimbursement rate compared to reimbursement target 81% - 100% Risk-adjusted discount rates 6.47% - 6.71% The change in fair value between December 31, 2023 and June 30, 2024 was a $0.9 million increase, and was primarily driven by changes in the risk-adjusted discount rates and the time value of money. The following table presents changes in the CVR liability for the periods presented (in thousands): CVR Liability Beginning balance as of December 31, 2023 $ 42,700 Changes in the fair value of the CVR liability 930 Payments (1,430) Ending Balance as of June 30, 2024 $ 42,200 Forward Contract Liability In connection with the Asset Acquisition, the Company entered into a contract for the issuance of 364,887 shares of Series A Preferred Stock as part of the consideration transferred. This forward contract was classified as a liability because the underlying preferred shares were contingently redeemable. The forward contract was carried at fair value on the balance sheet, with changes in fair value between the acquisition date and June 30, 2023 recorded in earnings. The liability was settled with the issuance of the Series A Preferred Stock on July 7, 2023. The fair value of the forward contract as of the acquisition date, June 22, 2023, was $106.2 million. The fair value of the forward contract on June 30, 2023 was $164.4 million. The $58.2 million change in fair value of the forward contract liability between the acquisition date and June 30, 2023, was recorded as Other Income (Expense) in the consolidated statements of operations for the three and six months ended June 30, 2023.

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	6 Months Ended
	Jun. 30, 2024
Cash and Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	Cash Equivalents and Marketable Securities The following tables summarize the estimated fair value of the Company’s cash equivalents and marketable securities and the gross unrealized gains and losses (in thousands): June 30, 2024 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 43,377 $ — $ — $ 43,377 Total cash equivalents $ 43,377 $ — $ — $ 43,377 Marketable securities: Commercial paper $ 119,844 $ 3 $ (131) $ 119,716 Corporate bonds 31,797 — (85) 31,712 U.S. government treasury securities 137,061 65 (269) 136,857 U.S. government agency securities 92,741 13 (188) 92,566 Total marketable securities $ 381,443 $ 81 $ (673) $ 380,851 December 31, 2023 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 150,648 $ — $ — $ 150,648 Commercial paper 24,950 5 — 24,955 U.S. government treasury securities 10,965 1 — 10,966 Total cash equivalents $ 186,563 $ 6 $ — $ 186,569 Marketable securities: Commercial paper $ 79,124 $ 62 $ — $ 79,186 Corporate bonds 32,984 81 (1) 33,064 U.S. government treasury securities 21,846 31 — 21,877 U.S. government agency securities 16,147 110 — 16,257 Total marketable securities $ 150,101 $ 284 $ (1) $ 150,384 The following table summarizes the available-for-sale securities in an unrealized loss position for which an allowance for credit losses has not been recorded as of June 30, 2024 and December 31, 2023, aggregated by major security type and length of time in a continuous unrealized loss position: June 30, 2024 Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Commercial paper $ 100,124 $ (131) $ — $ — $ 100,124 $ (131) Corporate bonds 31,712 (85) — — 31,712 (85) U.S. government treasury securities 93,432 (269) — — 93,432 (269) U.S. government agency securities 83,933 (188) — — 83,933 (188) Total marketable securities $ 309,201 $ (673) $ — $ — $ 309,201 $ (673) December 31, 2023 Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds $ 9,907 $ (1) $ — $ — $ 9,907 $ (1) U.S. government treasury securities 4,831 — — — 4,831 — Total marketable securities $ 14,738 $ (1) $ — $ — $ 14,738 $ (1) The Company evaluated its securities for credit losses and considered the decline in market value to be primarily attributable to current economic and market conditions and not to a credit loss or other factors. Additionally, the Company does not intend to sell the securities in an unrealized loss position and does not expect it will be required to sell the securities before recovery of the unamortized cost basis. As of June 30, 2024 and December 31, 2023, an allowance for credit losses had not been recognized. Given the Company's intent and ability to hold such securities until recovery, and the lack of significant change in credit risk of these investments, the Company does not consider these marketable securities to be impaired as of June 30, 2024 and December 31, 2023. The financial instruments that potentially subject the Company to a concentration of credit risk consist principally of cash deposits. Accounts at each of our two U.S. banking institutions are insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000 per depositor. As of June 30, 2024 and December 31, 2023, cash deposits at the Company's U.S. banking institutions exceeded the FDIC limits. Uninsured foreign cash deposits were immaterial for both periods. There were no realized gains or losses on marketable securities for the three and six months ended June 30, 2024 and 2023. Interest on marketable securities is included in interest income. Accrued interest receivable on available-for-sale debt securities as of June 30, 2024 and December 31, 2023, was $1.8 million and $0.9 million, respectively. The following table summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands): June 30, December 31, Due in one year or less $ 270,799 $ 115,784 Due in 1 - 2 years 110,052 34,600 Total marketable securities $ 380,851 $ 150,384 The Company may sell investments at any time for use in current operations even if they have not yet reached maturity. As a result, the Company classifies marketable securities, including securities with maturities beyond twelve months as current assets.

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	6 Months Ended
	Jun. 30, 2024
Payables and Accruals [Abstract]
Accrued and Other Current Liabilities	Accrued and Other Current Liabilities Accrued and other current liabilities consist of the following (in thousands): June 30, December 31, Accrued compensation $ 2,664 $ 4,054 Accrued contracted research and development costs 2,269 7,092 Accrued professional and consulting fees 515 1,474 Accrued other 235 488 Total accrued and other current liabilities $ 5,683 $ 13,108

Asset Acquisition

Asset Acquisition	6 Months Ended
	Jun. 30, 2024
Business Combination and Asset Acquisition [Abstract]
Asset Acquisition	Asset Acquisition On June 22, 2023, the Company acquired Pre-Merger Spyre pursuant to the Acquisition Agreement, by and among the Company, Aspen Merger Sub I, Inc., a Delaware corporation and a wholly owned subsidiary of the Company (“First Merger Sub”), Sequoia Merger Sub II, LLC, a Delaware limited liability company and wholly owned subsidiary of the Company (“Second Merger Sub”), and Pre-Merger Spyre. Pursuant to the Acquisition Agreement, First Merger Sub merged with and into Pre-Merger Spyre, pursuant to which Pre-Merger Spyre was the surviving corporation and became a wholly owned subsidiary of the Company (the “First Merger”). Immediately following the First Merger, Pre-Merger Spyre merged with and into Second Merger Sub, pursuant to which Second Merger Sub became the surviving entity. Pre-Merger Spyre was a pre-clinical stage biotechnology company that was incorporated on April 28, 2023 under the direction of Peter Harwin, a Managing Member of Fairmount, for the purpose of holding rights to certain intellectual property being developed by Paragon. Fairmount is a founder of Paragon. The Company completed the Asset Acquisition of Pre-Merger Spyre, in accordance with the terms of the Acquisition Agreement. Under the terms of the Acquisition Agreement, the Company issued 517,809 shares of Common Stock and 364,887 shares of Series A Preferred Stock to former Pre-Merger Spyre security holders. In addition, outstanding and unexercised stock options to purchase 2,734 shares of common stock were assumed from the Amended and Restated Spyre 2023 Equity Incentive Plan. At the acquisition date, the Company recorded forward contracts to represent the obligation to issue shares of Common Stock and shares of Series A Preferred Stock, respectively. The forward contract related to the Common Stock was recorded as Additional paid-in capital as the instrument is indexed to the Common Stock. The forward contract related to the Series A Preferred Stock was recorded as a liability, as the underlying stock has a cash redemption feature. On July 7, 2023, both the shares of Common Stock and Series A Preferred Stock were issued and the forward contract liability associated with the Series A Preferred Stock was settled accordingly. The Company concluded that the arrangement met the definition of an asset acquisition rather than a business combination, as substantially all of the fair value of the gross assets acquired was concentrated in a single identifiable asset, Pre-Merger Spyre's option to exclusively license certain intellectual property rights (the "Option"). The Company determined that the Option was a single asset as the Company's strategy relied on developing the entire portfolio of individual treatments to create combination treatments that simultaneously address different mechanisms of inflammatory bowel disease with a single treatment. The Company also determined that the pipeline candidates within the portfolio were similar in nature and risk profile. In addition, the Company did not obtain any substantive processes, assembled workforce, or employees capable of producing outputs in connection with the Asset Acquisition. The Company determined that the cost to acquire the asset was $113.3 million which was recorded as acquired in-process research and development ("IPR&D"). The fair value of the consideration issued consisted of the 364,887 shares of Series A Preferred Stock (14,595,480 shares of Common Stock on an as-converted basis) and 517,809 shares of Common Stock, valued at $291.08 per share and $7.277 per share, respectively. The Asset Acquisition costs are shown on the following table (in millions): June 22, Consideration transferred in Series A Preferred Stock and Common Stock $ 110.0 Transaction costs incurred by Pre-Merger Spyre 3.2 Fair value of Parapyre Option Obligation assumed by Pre-Merger Spyre 0.1 Total cost to acquire asset $ 113.3 The allocation of the purchase price to net assets acquired is as a follows: June 22, Acquired in-process research and development $ 130.5 Cash acquired 3.0 Assumed liabilities (20.2) Total cost to acquire asset $ 113.3

Licensing Agreements

Licensing Agreements	6 Months Ended
	Jun. 30, 2024
Licensing Agreements [Abstract]
Licensing Agreements	Licensing Agreements On July 12, 2023, December 14, 2023, and June 5, 2024, the Company exercised the Option available under the Paragon Agreement with respect to the SPY001, SPY002, and SPY003 research programs, respectively. On May 14, 2024, the Company and Paragon entered into (i) a license agreement (the “SPY001 License Agreement”), pursuant to which Paragon granted the Company a royalty-bearing, world-wide, exclusive license to develop, manufacture, commercialize or otherwise exploit certain antibodies and products targeting α4ß7 integrin and (ii) a license agreement (the “SPY002 License Agreement” and, together with the SPY001 License Agreement, the “License Agreements”), pursuant to which Paragon granted the Company a royalty- bearing, world-wide, exclusive license to develop, manufacture, commercialize or otherwise exploit certain licensed antibodies and products targeting TL1A, respectively. Under the terms of each License Agreement, the Company is obligated to pay Paragon up to $22.0 million based on specific development, regulatory and clinical milestones for each licensed research program, including a $1.5 million fee for nomination of a development candidate, as applicable, and a further milestone payment of $2.5 million upon the first dosing of a human patient in a Phase 1 trial. In addition, the following summarizes other key terms of each License Agreement: • Paragon will provide the Company with an exclusive license to its patents covering the related antibody, the method of use and its method of manufacture. • Paragon will not conduct any new campaigns that generate anti-α4ß7 or anti-TL1A monospecific antibodies for at least 5 years. • The Company will pay Paragon a low single-digit percentage royalty for single antibody products and a mid single-digit percentage royalty for products containing more than one antibody from Paragon. • There is a royalty step-down of 1/3rd if there is no Paragon patent in effect during the royalty term. • The royalty term ends on the later of (i) the last-to-expire licensed patent or Company patent directed to a derived antibody or (ii) 12 years from the date of first sale of a Company product. • Agreement may be terminated on 60 days’ notice by the Company; on material breach without cure; and to the extent permitted by law, on a party’s insolvency or bankruptcy. • With respect to the SPY002 License Agreement only, on a product by product basis, the Company will pay sublicensing fees of up to approximately $20 million upon the achievement of mostly commercial milestones. The SPY003 license agreement remains under negotiation as of the date of these consolidated financial statements. The Company recognizes the expense associated with each milestone when the achievement of the milestone is deemed probable. During the three and six months ended June 30, 2024, the Company recognized $5.5 million of expense related to Paragon license milestone payments recorded within Research and development expenses in the accompanying condensed statement of operations for the three and six months ended June 30, 2024. There was no such expense for the three and six months ended June 30, 2023. For the three and six months ended June 30, 2024, the Company made milestone payments totaling $3.0 million to Paragon. As of June 30, 2024, $2.5 million of Paragon license milestone payments were outstanding and payable to Paragon. Additionally, the Company recognized and paid $0.1 million related to sublicensing fees and which was recorded as Research and development expenses in the accompanying condensed statement of operations for the three and six months ended June 30, 2024.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Paragon and Parapyre each beneficially own less than 5% of the Company's capital stock through their respective holdings of the Company's Common Stock. Fairmount Funds Management LLC ("Fairmount") beneficially owns more than 5% of the Company's capital stock on an as-converted basis, has two seats on the Company's board of directors (the "Board") and beneficially owns more than 5% of Paragon, which is a joint venture between Fairmount and FairJourney Biologics. Fairmount appointed Paragon's board of directors and has the contractual right to approve the appointment of any executive officers. Parapyre is an entity formed by Paragon as a vehicle to hold equity in Spyre in order to share profits with certain employees of Paragon. The following is the summary of expenses related to the Paragon Agreement and License Agreements, which were ultimately settled in cash (in millions) and recorded within Research and development in the consolidated statement of operations for the periods presented: Three Months Ended Six Months Ended 2024 2023 2024 2023 Reimbursable costs under the Paragon Agreement $ 2.3 $ 1.2 $ 14.0 $ 1.2 License Agreements milestone and sublicensing fees 5.6 — 5.6 — Total related party expense $ 7.9 $ 1.2 $ 19.6 $ 1.2 The following is the summary of Related party accounts payable and other current liabilities (in millions): June 30, December 31, Reimbursable costs under the Paragon Agreement $ 1.2 $ 16.6 Parapyre warrants liability 6.9 — License Agreements development milestone liability (see Note 7) 2.5 — Total related party accounts payable $ 10.6 $ 16.6 Paragon Agreement In connection with the Asset Acquisition, the Company assumed the rights and obligations of Pre-Merger Spyre under the Paragon Agreement. Under the Paragon Agreement, Spyre is obligated to compensate Paragon for its services performed under each research program based on the actual costs incurred with mark-up costs pursuant to the terms of the Paragon Agreement. Spyre is also obligated under the Paragon Agreement to issue Parapyre annual equity grants of warrants in accordance with the Parapyre Option Obligation. For the three and six months ended June 30, 2024, the Company recognized expenses related to services provided by Paragon subsequent to the Asset Acquisition totaling $9.7 million and $26.8 million, respectively, which included $1.5 million and $6.9 million, respectively, of stock-based compensation expense, and were recorded as Research and development expenses in the consolidated statements of operations. For the three and six months ended June 30, 2024, the Company made payments totaling $11.3 million and $29.5 million respectively, in connection with the Paragon Agreement. On July 12, 2023, December 14, 2023, and June 5, 2024, the Company exercised the Option available under the Paragon Agreement with respect to the SPY001, SPY002 and SPY003 research programs, respectively. Our Option available under the Paragon Agreement with respect to the SPY004 program remains unexercised. Please refer to Note 7 for additional information on the License Agreements related to the exercised options. On May 14, 2024, the Company, Paragon and Parapyre entered into a second amended and restated antibody discovery and option agreement that amends and restates that certain amended and restated antibody discovery and option agreement, dated September 29, 2023, by and between Paragon, Parapyre and Spyre Therapeutics, LLC, in order to, among other things, (i) replace the Company’s subsidiary with the Company as a party to the agreement and (ii) amend certain terms related to the SPY003 research program, including without limitation, (a) establishing an SPY003 antibody selection process pursuant to which the Company and Paragon shall alternate in turn to select a project antibody to be included and excluded, respectively, from the Company’s rights under its option to license certain intellectual property rights related to SPY003 from Paragon until all project antibodies under the SPY003 research program have been selected; (b) reducing the development costs invoiced to the Company for the SPY003 research program incurred from and after April 1, 2024 through completion of the SPY003 antibody selection process by 50%; (c) requiring Paragon to reimburse the Company for 50% of the development costs for the SPY003 research program incurred prior to April 1, 2024; provided, that Paragon receives rights to at least one SPY003 project antibody following completion of the SPY003 antibody selection process; (d) obligating the Company to exercise its option to license the intellectual property rights to SPY003 project antibodies and technology following the completion of the SPY003 antibody selection process; and (e) establishing a license agreement term sheet for the SPY003 research program with substantially similar milestone payment terms and royalty payment terms as the SPY001 License Agreement. Please refer to Note 7 for additional disclosures. During the second quarter of 2024, the SPY003 antibody selection process was completed and the Company recognized a $5.9 million receivable and a corresponding reduction in Research and development expenses in its condensed consolidated statements of operations for the three and six ended June 30, 2024. As of June 30, 2024, the $5.9 million receivable was outstanding and included as a reduction to Related party accounts payable and other current liabilities on the Company's consolidated balance sheet. Parapyre Option Obligation Pursuant to the Paragon Agreement, the Company agreed to issue Parapyre an annual equity grant of warrants, on the last business day of each of the years ended December 31, 2023 and December 31, 2024, to purchase 1% of the then outstanding shares of the Company's Common Stock, on a fully diluted basis, during the term of the Paragon Agreement. Paragon License Agreements See Note 7 for disclosures related to the License Agreements entered into with Paragon. Mark McKenna Option Grant On February 1, 2024, the Board appointed Mark McKenna as a Class I director. Mr. McKenna and the Company are parties to a consulting agreement, pursuant to which Mr. McKenna agreed to continue to provide consulting services as an independent contractor to the Company, with an effective date of August 1, 2023 (the “Vesting Commencement Date”). As compensation for Mr. McKenna’s consulting services, on November 22, 2023, he was granted non-qualified stock options to purchase 477,000 shares of the Company’s Common Stock under the 2016 Plan (as defined in Note 8) with an exercise price of $10.39 per share, which vest as to 25% on the one year anniversary of the Vesting Commencement Date and thereafter vest and become exercisable in 36 equal monthly installments, subject to Mr. McKenna’s continued service to the Company through each applicable vesting date. For the three and six months ended June 30, 2024, the Company recognized $0.2 million and $0.5 million, respectively, in stock-based compensation expense related to Mr. McKenna's consulting agreement. There was no such expense for the three and six months ended June 30, 2023.

Convertible Preferred Stock and

Convertible Preferred Stock and Stockholders' Equity	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Convertible Preferred Stock and Stockholders' Equity	Convertible Preferred Stock and Stockholders’ Equity Pre-Funded Warrants In February 2019, April 2020 and May 2022, the Company issued pre-funded warrants to purchase the Company’s Common Stock in underwritten public offerings at the offering price of the Common Stock, less the $0.0025 per share exercise price of each warrant. The warrants were recorded as a component of stockholders’ (deficit) equity within additional paid-in capital and have no expiration date. Per the terms of the warrant agreements, the outstanding warrants to purchase shares of Common Stock may not be exercised if the holder’s ownership of the Company’s Common Stock would exceed 4.99% (“Maximum Ownership Percentage”), or 9.99% for certain holders. By written notice to the Company, each holder may increase or decrease the Maximum Ownership Percentage to any other percentage (not in excess of 19.99% for the majority of such warrants). The revised Maximum Ownership Percentage would be effective 61 days after the notice is received by the Company. As of June 30, 2024, all pre-funded warrants have been exercised and none remain outstanding. Parapyre Warrants The Company settled its 2023 obligations under the Parapyre Option Obligation by issuing Parapyre 684,407 warrants to purchase the Company's Common Stock, with a $21.52 per share exercise price for each warrant. Pursuant to the terms of the warrant agreement, the outstanding warrants to purchase shares of Common Stock may not be exercised if the holder’s ownership of the Company’s Common Stock would exceed 4.99%. As of June 30, 2024, none of the warrants issued under the Parapyre Option Obligation have been exercised. Series A Non-Voting Convertible Preferred Stock On June 22, 2023, the Company filed a Certificate of Designation of Preferences, Rights and Limitations of the Series A Preferred Stock with the Secretary of State of the State of Delaware (the “Series A Certificate of Designation”) in connection with the Asset Acquisition and the June 2023 PIPE. Pursuant to the Series A Certificate of Designation, holders of Series A Preferred Stock are entitled to receive dividends on shares of Series A Preferred Stock equal to, on an as-if-converted-to-Common Stock basis, and in the same form as, dividends actually paid on shares of Common Stock. Except as provided in the Series A Certificate of Designation or as otherwise required by law, the Series A Preferred Stock does not have voting rights. However, as long as any shares of Series A Preferred Stock are outstanding, the Company will not, without the affirmative vote of the holders of a majority of the then outstanding shares of the Series A Preferred Stock: (a) alter or change adversely the powers, preferences or rights given to the Series A Preferred Stock, or alter or amend the Series A Certificate of Designation, amend or repeal any provision of, or add any provision to, the Company’s Certificate of Incorporation or its Bylaws, or file any articles of amendment, certificate of designations, preferences, limitations and relative rights of any series of preferred stock, if such action would adversely alter or change the preferences, rights, privileges or powers of, or restrictions provided for the benefit of the Series A Preferred Stock, regardless of whether any of the foregoing actions will be by means of amendment to the Certificate of Incorporation or by merger, consolidation, recapitalization, reclassification, conversion or otherwise, (b) issue further shares of Series A Preferred Stock or increase or decrease (other than by conversion) the number of authorized shares of Series A Preferred Stock, (c) prior to the stockholder approval of the conversion of the Series A Preferred Stock into shares of Common Stock in accordance with Nasdaq Stock Market Rules (the “Series A Conversion Proposal”) or at any time while at least 30% of the originally issued Series A Preferred Stock remains issued and outstanding, consummate (x) any Fundamental Transaction (as defined in the Series A Certificate of Designation) or (y) any merger or consolidation of the Company with or into another entity or any stock sale to, or other business combination in which our stockholders immediately before such transaction do not hold at least a majority of our capital stock immediately after such transaction or (d) enter into any agreement with respect to any of the foregoing. The Series A Preferred Stock does not have a preference upon any liquidation, dissolution or winding-up of the Company. On June 26, 2023, the Company completed a private placement of 721,452 shares of Series A Preferred Stock in exchange for gross proceeds of approximately $210.0 million, or net proceeds of $197.3 million, after deducting placement agent and other offering costs. On July 7, 2023, the Company issued 364,887 shares of Series A Preferred Stock as part of its consideration transferred in connection with the Asset Acquisition that closed on June 22, 2023 which settled the related forward contract liability. On November 21, 2023, the Company's stockholders approved the Series A Conversion Proposal, among other matters, at a special meeting of stockholders. As a result of the approval of the Series A Conversion Proposal, all conditions that could have required cash redemption of the Series A Preferred Stock were satisfied. Since the Series A Preferred Stock is no longer redeemable, the associated balances of the Series A Preferred Stock were reclassified from mezzanine equity to permanent equity during the fourth quarter of 2023. Following stockholder approval of the Series A Conversion Proposal, each share of Series A Preferred Stock automatically converted into 40 shares of Common Stock, subject to certain limitations, including that a holder of Series A Preferred Stock is prohibited from converting shares of Series A Preferred Stock into shares of Common Stock if, as a result of such conversion, such holder, together with its affiliates, would beneficially own more than a specified percentage (established by the holder between 0.0% and 19.9%) of the total number of shares of Common Stock issued and outstanding immediately after giving effect to such conversion. 649,302 shares of Series A Preferred Stock automatically converted to 25,972,080 shares of Common Stock; 437,037 shares of Series A Preferred Stock did not automatically convert and remained outstanding following the conversion. This conversion was recorded as a reclassification between Series A Preferred Stock and Common Stock based on the historical per-share contributed capital amount of the Series A Preferred Stock. On April 23, 2024, in connection with the April 2024 Exchange, the Stockholder agreed to exchange an aggregate of 90,992 shares of Series A Preferred Stock for an aggregate of 3,639,680 shares of the Company's Common Stock. This exchange was recorded as a reclassification between Series A Preferred Stock and Common Stock based on the historical per-share contributed capital amount, inclusive of any forward-contract valuation adjustments, of the Series A Preferred Stock. Following the April 2024 Exchange, 346,045 shares of Series A Preferred Stock remained outstanding. Series B Non-Voting Convertible Preferred Stock On December 8, 2023, the Company filed a Certificate of Designation of Preferences, Rights and Limitations of Series B Non-Voting Convertible Preferred Stock with the Secretary of State of the State of Delaware (the “Series B Certificate of Designation”) in connection with the December 2023 PIPE. Pursuant to the Series B Certificate of Designation, holders of Series B Preferred Stock are entitled to receive dividends on shares of Series B Preferred Stock equal to, on an as-if-converted-to-Common Stock basis, and in the same form as, dividends actually paid on shares of Common Stock. Except as provided in the Series B Certificate of Designation or as otherwise required by law, the Series B Preferred Stock does not have voting rights. However, as long as any shares of Series B Preferred Stock are outstanding, the Company will not, without the affirmative vote of the holders of a majority of the then outstanding shares of the Series B Preferred Stock, alter or change adversely the powers, preferences or rights given to the Series B Preferred Stock, or alter or amend the Series B Certificate of Designation, amend or repeal any provision of, or add any provision to, the Company’s Certificate of Incorporation or its Bylaws, or file any articles of amendment, certificate of designations, preferences, limitations and relative rights of any series of preferred stock, if such action would adversely alter or change the preferences, rights, privileges or powers of, or restrictions provided for the benefit of the Series B Preferred Stock, regardless of whether any of the foregoing actions will be by means of amendment to the Certificate of Incorporation or by merger, consolidation, recapitalization, reclassification, conversion or otherwise. The Series B Preferred Stock does not have a preference upon any liquidation, dissolution or winding-up of the Company. On December 11, 2023, as part of the December 2023 PIPE, the Company completed a private placement of 150,000 shares of Series B Preferred Stock in exchange for gross proceeds of $90.0 million. On March 18, 2024, in connection with the March 2024 PIPE, the Company filed a certificate of amendment to its Series B Certificate of Designation to increase the number of authorized shares of Series B Preferred Stock from 150,000 to 271,625. On March 20, 2024, as part of the March 2024 PIPE, the Company completed a private placement of 121,625 shares of Series B Preferred Stock in exchange for gross proceeds of approximately $180.0 million. On May 14, 2024, the Company's stockholders approved the issuance of Common Stock upon the conversion of all issued and outstanding Series B Preferred Stock into shares of Common Stock in accordance with the Nasdaq Stock Market Rules (the "Series B Conversion Proposal"), among other matters, at its 2024 annual meeting of stockholders. As a result of the approval of the Series B Conversion Proposal, all conditions that could have required cash redemption of the Series B Preferred Stock were satisfied. Since the Series B Preferred Stock is no longer redeemable, the associated balances of the Series B Preferred Stock were reclassified from mezzanine equity to permanent equity during the second quarter of 2024. Following stockholder approval of the Series B Conversion Proposal, each share of Series B Preferred Stock automatically converted into 40 shares of the Common Stock, subject to certain limitations, including that a holder of Series B Preferred Stock is prohibited from converting shares of Series B Preferred Stock into shares of Common Stock if, as a result of such conversion, such holder, together with its affiliates, would beneficially own more than a specified percentage (established by the holder between 0.0% and 19.9%) of the total number of shares of Common Stock issued and outstanding immediately after giving effect to such conversion. 254,958 shares of Series B Preferred Stock automatically converted to 10,198,320 shares of Common Stock; 16,667 shares of Series B Preferred Stock did not automatically convert and remain outstanding as of June 30, 2024 due to beneficial ownership limitations. This conversion was recorded as a reclassification between Series B Preferred Stock and Common Stock based on the historical per-share contributed capital amount of the Series B Preferred Stock.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2015 Equity Incentive Plan In March 2015, the Company adopted the 2015 Equity Incentive Plan (“2015 Plan”), administered by the board of directors, and provides for the Company to sell or issue share of Common Stock or restricted Common Stock, or to grant incentive stock options or nonqualified stock options for the purchase of Common Stock, to employees, members of the board of directors and consultants of the Company. The Company granted options under the 2015 Plan until April 2016 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2015 Plan. As of June 30, 2024, a total of 3,029 shares of Common Stock are subject to options outstanding under the 2015 Plan and will become available under the 2016 Equity Incentive Plan (“2016 Plan”) to the extent the options are forfeited or lapse unexercised. 2016 Equity Incentive Plan The 2016 Plan became effective in April 2016 and serves as the successor to the 2015 Plan. Under the 2016 Plan, the Company may grant stock options, stock appreciation rights, restricted stock awards, restricted stock units, performance awards, and stock bonuses. The 2016 Plan, as amended, provides for an automatic increase in the number of shares reserved for issuance thereunder on January 1 of each year for the remaining term of the plan equal to (a) 5.0% of the number of issued and outstanding shares of Common Stock (including such shares issuable pursuant to the exercise or conversion, as applicable, of any outstanding pre-funded warrants and nonvoting convertible preferred stock) on December 31 of the immediately preceding year, or (b) a lesser amount as approved by the board each year (the “Evergreen Provision”). As a result of the Evergreen Provision, on January 1, 2024 and 2023, an additional 3,023,650 and 104,561 shares, respectively, became available for issuance under the 2016 Plan. As of June 30, 2024, the 2016 Plan had 7,336,181 shares available for future issuance, of which 3,024,766 shares were subject to outstanding option awards. 2018 Equity Inducement Plan The 2018 Equity Inducement Plan (“2018 Plan”) became effective in February 2018. As of June 30, 2024, the 2018 Plan had 6,028,000 shares available for future issuance, of which 5,682,341 shares were subject to outstanding option awards and restricted unit awards. Service-based awards granted under the 2018 Plan, 2016 Plan, and 2015 Plan generally vest over four years and expire after ten years, although awards have been granted with vesting terms less than four years. Under the 2016 Plan and 2018 Plan, the Company may grant stock-based awards with service conditions (“service-based” awards), performance conditions (“performance-based” awards), and market conditions (“market-based” awards). Spyre 2023 Equity Incentive Plan On June 22, 2023, in connection with the Asset Acquisition, the Company assumed the Amended and Restated Spyre 2023 Equity Incentive Plan and its outstanding and unexercised stock options, which were converted to options to purchase 2,734 shares of Common Stock. The acquisition-date fair value of these grants will be recognized as an expense on a pro-rata basis over the vesting period. The following table summarizes the Company’s stock awards granted under all equity incentive and inducement plans for each of the periods indicated: Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 387,695 $ 36.42 2,536,697 $ 7.50 1,432,353 $ 29.19 2,714,317 $ 7.75 Parapyre Option Obligation As of June 30, 2024, the pro-rated estimated fair value of the options to be granted on December 31, 2024 related to the Parapyre Option Obligation, was approximately $6.9 million. For the three and six months ended June 30, 2024, $1.5 million and $6.9 million was recognized as stock compensation expense related to the Parapyre Option Obligation. For the three and six months ended June 30, 2023, $0.2 million was recognized as stock compensation expense related to the Parapyre Option Obligation. As of June 30, 2024, the unamortized expense related to the Parapyre Option Obligation was $7.0 million. 2016 Employee Stock Purchase Plan Under the Company’s 2016 Employee Stock Purchase Plan (“2016 ESPP”), the Company issued and sold 2,330 and 1,793 shares during the six months ended June 30, 2024 and June 30, 2023, respectively. The aggregate cash proceeds were not material for both periods. Stock-based Compensation Expense Total stock-based compensation expense recognized from the Company’s equity incentive plans, 2018 Plan, 2016 ESPP and Parapyre Option Obligation during the periods presented was as follows (in thousands): Three Months Ended Six Months Ended 2024 2023 2024 2023 Research and development (1) $ 3,451 $ 394 $ 10,308 $ 1,171 General and administrative 5,231 1,517 12,209 2,449 Total stock-based compensation expense (2) $ 8,682 $ 1,911 $ 22,517 $ 3,620 (1) For the three and six months ended June 30, 2024, $1.5 million and $6.9 million, respectively, was recognized as stock compensation expense related to the Parapyre Option Obligation. For the three and six months ended June 30, 2023, $0.2 million was recognized as stock compensation expense related to the Parapyre Option Obligation. (2) Of the total $8.7 million and $22.5 million of stock-based compensation expense for the three and six months ended June 30, 2024, $0.7 million and $3.8 million, respectively, is related to legacy Aeglea employees and directors who had been terminated as of the end of the respective period. Of the total $1.9 million and $3.6 million of stock-based compensation expense for the three and six months ended June 30, 2023, $1.8 million and $3.5 million, respectively, is related to legacy Aeglea employees and directors who had been terminated as of the end of the period. The following table summarizes the weighted-average Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted under the Company's equity incentive plans, and the shares purchasable under the 2016 ESPP during the periods presented: Three Months Ended Six Months Ended 2024 2023 2024 2023 Stock Options Granted Expected term (in years) 5.92 6.03 6.00 6.03 Expected volatility 104% 117% 105% 115% Risk-free interest 4.35% 3.98% 4.01% 3.99% Dividend yield — — — — 2016 ESPP Expected term (in years) 0.50 0.49 Expected volatility 98% 181% Risk-free interest 5.31% 4.99% Dividend yield — —

Legacy Strategic License Agreem

Legacy Strategic License Agreements	6 Months Ended
	Jun. 30, 2024
License And Collaboration Agreement [Abstract]
Legacy Strategic License Agreements	Legacy Strategic License Agreements On March 21, 2021, the Company entered into an exclusive license and supply agreement with Immedica (the "Immedica Agreement"). On July 27, 2023, the Company announced that it had entered into an agreement to sell the global rights to pegzilarginase, an investigational treatment for the rare metabolic disease Arginase 1 Deficiency, to Immedica for $15.0 million in upfront cash proceeds and up to $100.0 million in contingent milestone payments. The sale of pegzilarginase to Immedica superseded and terminated the Immedica Agreement. The milestone payments are contingent on formal reimbursement decisions by national authorities in key European markets and pegzilarginase approval by the FDA, among other events. In addition to the payment previously made to holders of the Company's CVRs (as defined in Note 1) related to the upfront cash proceeds, any contingent milestone payments under the Immedica Agreement, if paid within the CVR period, will be distributed to holders of the Company's CVRs net of expenses and adjustments pursuant to the contingent value rights agreement we entered into with Equiniti Trust Company LLC (f/k/a American Stock Transfer & Trust Company LLC) as rights agent in connection with the Asset Acquisition. The Company did not recognize any revenue under the Immedica Agreement for the three and six months ended June 30, 2024. For the three and six months ended June 30, 2023, the Company recognized $0.7 million and $0.9 million, respectively, of development fee revenue in connection with the Immedica Agreement, which was attributable to the PEACE Phase 3 trial and BLA package for pegzilarginase. For more details on the Immedica Agreement, which was terminated on July 27, 2023, please refer to the Note under Item 1 of Part I, titled "12. Strategic License Agreements" of the Company's Annual Report. Contract Balances from Customer Contract The timing of revenue recognition, billings and cash collections results in contract assets and contract liabilities on the Company's balance sheets. The Company recognizes license and development receivables based on billed services, which are derecognized upon reimbursement. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded. Contract liabilities are recognized as revenue after control of the goods or services is transferred to the customer and all revenue recognition criteria have been met. The Company did not have any contract assets or liabilities as of June 30, 2024 and December 31, 2023.

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 The Company computes net loss attributable per common stockholder using the two-class method required for participating securities. The Company considers convertible preferred stock to be participating securities. In the event that the Company paid out distributions, holders of convertible preferred stock would participate in the distribution. The two-class method is an earnings (loss) allocation method under which earnings (loss) per share is calculated for Common Stock and participating security considering a participating security’s rights to undistributed earnings (loss) as if all such earnings (loss) had been distributed during the period. The holders of Series A Preferred Stock and Series B Preferred Stock do not have an obligation to fund losses and therefore the Series A Preferred Stock and the Series B Preferred Stock were excluded from the calculation of basic net loss per share. Basic and diluted net loss per share is computed by dividing the net loss by the weighted-average number of Common Stock and pre-funded warrants outstanding during the period, without consideration of potential dilutive securities. The pre-funded warrants are included in the computation of basic net loss per share as the exercise price is negligible and they are fully vested and exercisable. For periods in which the Company generated a net loss, the Company does not include the potential impact of dilutive securities in diluted net loss per share, as the impact of these items is anti-dilutive. The Company has generated a net loss for all periods presented, therefore diluted net loss per share is the same as basic net loss per share since the inclusion of potentially dilutive securities would be anti-dilutive. The following weighted-average equity instruments were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the periods presented: Three Months Ended Six Months Ended 2024 2023 2024 2023 Options to purchase common stock 5,010,436 654,527 4,526,643 557,515 Unvested restricted stock units 79,870 — 71,368 381 Outstanding Parapyre warrants 684,407 — 684,407 — Series A Preferred Stock (1) 14,801,716 — 16,141,598 — Series B Preferred Stock (1) 351,655 — 175,828 — (1) Assumes each share is converted to 40 shares of Common Stock, in accordance with the terms of the respective certificate of designation without regard to any beneficial ownership limitations. The following is a reconciliation of the shares used as the denominator for the calculation of basic and diluted net loss per share: Three Months Ended Six Months Ended 2024 2023 2024 2023 Weighted average Common Stock 45,214,616 2,711,439 40,738,639 2,663,408 Weighted average pre-funded warrants 101,648 1,111,166 175,824 1,133,291 Total basic and diluted weighted average shares 45,316,264 3,822,605 40,914,463 3,796,699

Restructuring Charges

Restructuring Charges	6 Months Ended
	Jun. 30, 2024
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring Charges Severance and Stock Compensation On April 12, 2023, based on the review of the inconclusive interim results from the Company's Phase 1/2 clinical trial of pegtarviliase for the treatment of classical homocystinuria and other business considerations, the Company announced that it had initiated a process to explore strategic alternatives to maximize stockholder value and engaged an independent exclusive financial advisor to support this process. As a result, the Company implemented a restructuring plan resulting in an approximate 83% reduction of the Company’s existing headcount by June 30, 2023. The Company recognized restructuring expenses consisting of cash severance payments and other employee-related costs of $6.4 million during the three and six months ended June 30, 2023, respectively. In addition, the Company recognized $1.0 million in non-cash stock-based compensation expense related to the accelerated vesting of stock-based awards for certain employees. The Company recorded these restructuring charges based on each employee’s role to the respective research and development and general and administrative operating expense categories on its condensed consolidated statements of operations and comprehensive loss. Sale of Assets During the second quarter of 2023, the Company sold various lab equipment, consumables, and furniture and fixtures for total consideration of $0.5 million. After recording the disposal of all property and equipment net of proceeds, the Company recorded a $0.7 million and $0.2 million loss on disposal of long lived assets which is included in Research and development and General and administrative expenses, respectively. Lease Right-of-use Asset and Leasehold Improvement Impairment Effective June 30, 2023, the Company abandoned its leased office space in Austin, Texas. As a result, the Company recognized an impairment loss of $0.9 million related to the operating lease right-of-use asset and $1.7 million related to leasehold improvements. On August 7, 2023, the Company terminated its building lease in Austin, Texas. The negotiated termination agreement obligated the Company to pay the lessor a $2.0 million termination fee in exchange for releasing the Company of all further obligations under the lease. All charges related to the restructuring activities were recognized during the second quarter of 2023. No further restructuring charges were incurred under the restructuring plan. A summary of the charges related to the restructuring activities is as follows (in thousands): Severance Related Expenses Stock Compensation Expenses Loss on Disposal of Long Lived Assets Lease Asset Impairment Total Restructuring Costs Research and development $ 3,182 $ 123 $ 749 $ 1,405 $ 5,459 General and administrative 3,266 870 182 1,175 5,493 Total $ 6,448 $ 993 $ 931 $ 2,580 $ 10,952 As of December 31, 2023, $1.1 million of restructuring costs remained outstanding and unpaid. As of June 30, 2024, there were no remaining liabilities under the restructuring plan described above.

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	$ (38,837)	$ (43,857)	$ (217,081)	$ (18,422)	$ (82,694)	$ (235,503)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended	6 Months Ended
	Jun. 30, 2024 shares	Jun. 30, 2024 shares
Trading Arrangements, by Individual
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Cameron Turtle [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On April 12, 2024, Cameron Turtle, the Company's Chief Executive Officer, adopted a trading plan intended to satisfy Rule 10b5-1(c) to sell up to 300,000 shares of Common Stock over a period ending November 19, 2026, subject to certain conditions, all of which shares are to be acquired upon the exercise of employee stock options.
Name	Cameron Turtle
Title	Chief Executive Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	April 12, 2024
Arrangement Duration	951 days
Aggregate Available	300,000	300,000
Scott Burrows [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On April 15, 2024, Scott Burrows, the Company's Chief Financial Officer, adopted a trading plan intended to satisfy Rule 10b5-1(c) to sell up to 180,000 shares of Common Stock over a period ending November 19, 2026, subject to certain conditions, all of which shares are to be acquired upon the exercise of employee stock options.
Name	Scott Burrows
Title	Company's Chief Financial Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	April 15, 2024
Arrangement Duration	948 days
Aggregate Available	180,000	180,000
Jeffrey Albers [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On April 16, 2024, Jeffrey Albers, a member of the Company's Board of Directors, and Sessions LLC, an investment company of which Mr. Albers is a managing director and owns 10% or more of the equity interest in or otherwise exercises significant influence over, adopted a trading plan intended to satisfy Rule 10b5-1(c) to sell up to 22,500 shares of Common Stock over a period ending April 30, 2025, subject to certain conditions, 7,500 of which shares are to be acquired upon the exercise of director stock options.
Name	Jeffrey Albers
Title	member of the Company's Board of Directors
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	April 16, 2024
Arrangement Duration	379 days
Total Shares of Common Stock Available To Sell [Member]
Trading Arrangements, by Individual
Aggregate Available	22,500	22,500
Component of Shares Available To Be Acquired From Stock Options [Member] | Jeffrey Albers [Member]
Trading Arrangements, by Individual
Aggregate Available	7,500	7,500

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 The consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States (“U.S. GAAP”) as defined by the Financial Accounting Standards Board and include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Reclassification of Prior Year Presentation	Reclassification of Prior Year Presentation Certain prior year amounts have been reclassified for consistency with the current year presentation. These reclassifications had no effect on the reported results of operations or balance sheets.
License Agreements Contingent Milestone Payments	License Agreements Contingent Milestone Payments The Company’s license agreements include specific development, regulatory, and clinical milestone payments that are payable upon the resolution of a contingency, such as upon the selection of a development candidate, first dosing of a human patient in clinical trials or receipt of the Food Drug and Administration’s (“FDA”) approval of a Spyre drug. The achievement of these milestone payments involves many factors outside of the Company’s control and therefore the associated likelihood cannot be considered probable until the related contingency is resolved. Based on the preceding, the Company accrues each milestone payment upon the achievement of the applicable milestone event.
Recently Adopted Accounting Pronouncement	Recently Adopted Accounting Pronouncement There have been no recent accounting pronouncements or changes in accounting pronouncements during the six months ended June 30, 2024 that are of significance or potential significance to the Company.
Net Loss Per Share	The Company computes net loss attributable per common stockholder using the two-class method required for participating securities. The Company considers convertible preferred stock to be participating securities. In the event that the Company paid out distributions, holders of convertible preferred stock would participate in the distribution. The two-class method is an earnings (loss) allocation method under which earnings (loss) per share is calculated for Common Stock and participating security considering a participating security’s rights to undistributed earnings (loss) as if all such earnings (loss) had been distributed during the period. The holders of Series A Preferred Stock and Series B Preferred Stock do not have an obligation to fund losses and therefore the Series A Preferred Stock and the Series B Preferred Stock were excluded from the calculation of basic net loss per share.

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables set forth the fair value of the Company’s financial assets and liabilities at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands): June 30, 2024 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 43,377 $ — $ — $ 43,377 U.S. government treasury securities 136,857 — — 136,857 U.S. government agency securities — 92,566 — 92,566 Commercial paper — 119,716 — 119,716 Corporate bonds — 31,712 — 31,712 Total financial assets $ 180,234 $ 243,994 $ — $ 424,228 Liabilities: Parapyre Option Obligation $ — $ 6,889 $ — $ 6,889 CVR liability — — 42,200 42,200 Total liabilities $ — $ 6,889 $ 42,200 $ 49,089 December 31, 2023 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 150,648 $ — $ — $ 150,648 U.S. government treasury securities 32,843 — — 32,843 U.S. government agency securities — 16,257 — 16,257 Commercial paper — 104,141 — 104,141 Corporate bonds — 33,064 — 33,064 Total financial assets $ 183,491 $ 153,462 $ — $ 336,953 Liabilities: CVR liability $ — $ — $ 42,700 $ 42,700 Total liabilities $ — $ — $ 42,700 $ 42,700
Significant Inputs used to Estimate the Fair Value of Derivative Liabilities	The significant inputs used to estimate the fair value of the CVR liability were as follows: June 30, 2024 Estimated cash flow dates 02/15/25 - 06/22/26 Estimated probability of success 39% - 100% Estimated reimbursement rate compared to reimbursement target 81% - 100% Risk-adjusted discount rates 6.47% - 6.71%
Changes in Derivative Liabilities	The following table presents changes in the CVR liability for the periods presented (in thousands): CVR Liability Beginning balance as of December 31, 2023 $ 42,700 Changes in the fair value of the CVR liability 930 Payments (1,430) Ending Balance as of June 30, 2024 $ 42,200

Cash Equivalents and Marketab_2

Cash Equivalents and Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2024
Cash and Cash Equivalents [Abstract]
Estimated Fair Value of Cash Equivalents and Marketable Securities and the Gross Unrealized Gains and Losses	The following tables summarize the estimated fair value of the Company’s cash equivalents and marketable securities and the gross unrealized gains and losses (in thousands): June 30, 2024 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 43,377 $ — $ — $ 43,377 Total cash equivalents $ 43,377 $ — $ — $ 43,377 Marketable securities: Commercial paper $ 119,844 $ 3 $ (131) $ 119,716 Corporate bonds 31,797 — (85) 31,712 U.S. government treasury securities 137,061 65 (269) 136,857 U.S. government agency securities 92,741 13 (188) 92,566 Total marketable securities $ 381,443 $ 81 $ (673) $ 380,851 December 31, 2023 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Cash equivalents: Money market funds $ 150,648 $ — $ — $ 150,648 Commercial paper 24,950 5 — 24,955 U.S. government treasury securities 10,965 1 — 10,966 Total cash equivalents $ 186,563 $ 6 $ — $ 186,569 Marketable securities: Commercial paper $ 79,124 $ 62 $ — $ 79,186 Corporate bonds 32,984 81 (1) 33,064 U.S. government treasury securities 21,846 31 — 21,877 U.S. government agency securities 16,147 110 — 16,257 Total marketable securities $ 150,101 $ 284 $ (1) $ 150,384
Available-for-Sale Securities in an Unrealized Loss Position	The following table summarizes the available-for-sale securities in an unrealized loss position for which an allowance for credit losses has not been recorded as of June 30, 2024 and December 31, 2023, aggregated by major security type and length of time in a continuous unrealized loss position: June 30, 2024 Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Commercial paper $ 100,124 $ (131) $ — $ — $ 100,124 $ (131) Corporate bonds 31,712 (85) — — 31,712 (85) U.S. government treasury securities 93,432 (269) — — 93,432 (269) U.S. government agency securities 83,933 (188) — — 83,933 (188) Total marketable securities $ 309,201 $ (673) $ — $ — $ 309,201 $ (673) December 31, 2023 Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds $ 9,907 $ (1) $ — $ — $ 9,907 $ (1) U.S. government treasury securities 4,831 — — — 4,831 — Total marketable securities $ 14,738 $ (1) $ — $ — $ 14,738 $ (1)
Contractual Maturities of Marketable Securities at Estimated Fair Value	The following table summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands): June 30, December 31, Due in one year or less $ 270,799 $ 115,784 Due in 1 - 2 years 110,052 34,600 Total marketable securities $ 380,851 $ 150,384

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2024
Payables and Accruals [Abstract]
Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): June 30, December 31, Accrued compensation $ 2,664 $ 4,054 Accrued contracted research and development costs 2,269 7,092 Accrued professional and consulting fees 515 1,474 Accrued other 235 488 Total accrued and other current liabilities $ 5,683 $ 13,108

Asset Acquisition (Tables)

Asset Acquisition (Tables)	6 Months Ended
	Jun. 30, 2024
Business Combination and Asset Acquisition [Abstract]
Asset Acquisition Cost	The Asset Acquisition costs are shown on the following table (in millions): June 22, Consideration transferred in Series A Preferred Stock and Common Stock $ 110.0 Transaction costs incurred by Pre-Merger Spyre 3.2 Fair value of Parapyre Option Obligation assumed by Pre-Merger Spyre 0.1 Total cost to acquire asset $ 113.3 The allocation of the purchase price to net assets acquired is as a follows: June 22, Acquired in-process research and development $ 130.5 Cash acquired 3.0 Assumed liabilities (20.2) Total cost to acquire asset $ 113.3

Related Party Transactions (Tab

Related Party Transactions (Tables)	6 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
Expenses related to Related Party which were Settled in Cash	The following is the summary of expenses related to the Paragon Agreement and License Agreements, which were ultimately settled in cash (in millions) and recorded within Research and development in the consolidated statement of operations for the periods presented: Three Months Ended Six Months Ended 2024 2023 2024 2023 Reimbursable costs under the Paragon Agreement $ 2.3 $ 1.2 $ 14.0 $ 1.2 License Agreements milestone and sublicensing fees 5.6 — 5.6 — Total related party expense $ 7.9 $ 1.2 $ 19.6 $ 1.2
Related Party Accounts Payable	The following is the summary of Related party accounts payable and other current liabilities (in millions): June 30, December 31, Reimbursable costs under the Paragon Agreement $ 1.2 $ 16.6 Parapyre warrants liability 6.9 — License Agreements development milestone liability (see Note 7) 2.5 — Total related party accounts payable $ 10.6 $ 16.6

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]
Stock Awards Granted	The following table summarizes the Company’s stock awards granted under all equity incentive and inducement plans for each of the periods indicated: Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 387,695 $ 36.42 2,536,697 $ 7.50 1,432,353 $ 29.19 2,714,317 $ 7.75
Stock-Based Compensation Expense	Total stock-based compensation expense recognized from the Company’s equity incentive plans, 2018 Plan, 2016 ESPP and Parapyre Option Obligation during the periods presented was as follows (in thousands): Three Months Ended Six Months Ended 2024 2023 2024 2023 Research and development (1) $ 3,451 $ 394 $ 10,308 $ 1,171 General and administrative 5,231 1,517 12,209 2,449 Total stock-based compensation expense (2) $ 8,682 $ 1,911 $ 22,517 $ 3,620 (1) For the three and six months ended June 30, 2024, $1.5 million and $6.9 million, respectively, was recognized as stock compensation expense related to the Parapyre Option Obligation. For the three and six months ended June 30, 2023, $0.2 million was recognized as stock compensation expense related to the Parapyre Option Obligation. (2) Of the total $8.7 million and $22.5 million of stock-based compensation expense for the three and six months ended June 30, 2024, $0.7 million and $3.8 million, respectively, is related to legacy Aeglea employees and directors who had been terminated as of the end of the respective period. Of the total $1.9 million and $3.6 million of stock-based compensation expense for the three and six months ended June 30, 2023, $1.8 million and $3.5 million, respectively, is related to legacy Aeglea employees and directors who had been terminated as of the end of the period.
Assumptions used to Estimate the Fair Value of Stock Options Granted	The following table summarizes the weighted-average Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted under the Company's equity incentive plans, and the shares purchasable under the 2016 ESPP during the periods presented: Three Months Ended Six Months Ended 2024 2023 2024 2023 Stock Options Granted Expected term (in years) 5.92 6.03 6.00 6.03 Expected volatility 104% 117% 105% 115% Risk-free interest 4.35% 3.98% 4.01% 3.99% Dividend yield — — — — 2016 ESPP Expected term (in years) 0.50 0.49 Expected volatility 98% 181% Risk-free interest 5.31% 4.99% Dividend yield — —

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
Weighted-Average Equity Instruments Excluded from Calculation of Diluted Net Loss Per Share	The following weighted-average equity instruments were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the periods presented: Three Months Ended Six Months Ended 2024 2023 2024 2023 Options to purchase common stock 5,010,436 654,527 4,526,643 557,515 Unvested restricted stock units 79,870 — 71,368 381 Outstanding Parapyre warrants 684,407 — 684,407 — Series A Preferred Stock (1) 14,801,716 — 16,141,598 — Series B Preferred Stock (1) 351,655 — 175,828 — (1) Assumes each share is converted to 40 shares of Common Stock, in accordance with the terms of the respective certificate of designation without regard to any beneficial ownership limitations.
Reconciliation of Basic and Diluted Net Loss Per Share	The following is a reconciliation of the shares used as the denominator for the calculation of basic and diluted net loss per share: Three Months Ended Six Months Ended 2024 2023 2024 2023 Weighted average Common Stock 45,214,616 2,711,439 40,738,639 2,663,408 Weighted average pre-funded warrants 101,648 1,111,166 175,824 1,133,291 Total basic and diluted weighted average shares 45,316,264 3,822,605 40,914,463 3,796,699

Restructuring Charges (Tables)

Restructuring Charges (Tables)	6 Months Ended
	Jun. 30, 2024
Restructuring and Related Activities [Abstract]
Charges Related to the Restructuring Activities	A summary of the charges related to the restructuring activities is as follows (in thousands): Severance Related Expenses Stock Compensation Expenses Loss on Disposal of Long Lived Assets Lease Asset Impairment Total Restructuring Costs Research and development $ 3,182 $ 123 $ 749 $ 1,405 $ 5,459 General and administrative 3,266 870 182 1,175 5,493 Total $ 6,448 $ 993 $ 931 $ 2,580 $ 10,952

The Company and Basis of Pres_2

The Company and Basis of Presentation (Details) $ / shares in Units, $ in Thousands

1 Months Ended

3 Months Ended

6 Months Ended

109 Months Ended

May 14, 2024 shares

Apr. 23, 2024 shares

Mar. 20, 2024 USD ($) shares

Mar. 18, 2024 shares

Dec. 11, 2023 USD ($) $ / shares shares

Nov. 21, 2023 shares

Sep. 08, 2023

Jun. 26, 2023 USD ($) shares

Jun. 22, 2023 $ / shares shares

Apr. 30, 2023

Jun. 30, 2024 USD ($) $ / shares shares

Mar. 31, 2024 shares

Jun. 30, 2023 shares

Jun. 30, 2024 USD ($) segment $ / shares shares

Mar. 31, 2024 USD ($) shares

Apr. 25, 2024 shares

Dec. 31, 2023 USD ($) $ / shares shares

Nov. 22, 2023 shares

Company and Basis of Presentation [Line Items]

Number of operating segments | segment

1

Employee workforce, termination percentage

83%

83%

Common stock, par value (in dollars per share) | $ / shares

$ 0.0001

$ 0.0001

$ 0.0001

Series B non-voting convertible preferred stock, par value (in dollars per share) | $ / shares

$ 0.0001

Proceeds from raising capital | $

$ 1,100,000

Accumulated deficit | $

$ 847,108

$ 847,108

$ 764,414

Cash, cash equivalents, and marketable securities | $

$ 426,300

$ 426,300

Asset Acquisition

Company and Basis of Presentation [Line Items]

Fixed exchange ratio

54.94488%

Spyre Therapeutics, Inc.

Company and Basis of Presentation [Line Items]

Asset acquisition, stockholder payment period

3 years

Asset acquisition, cash payment, threshold period

1 year

Spyre 2023 Equity Incentive Plan | Asset Acquisition

Company and Basis of Presentation [Line Items]

Number of outstanding and unexercised stock options to purchase (in shares)

2,734

Spyre 2023 Equity Incentive Plan | Spyre Therapeutics, Inc.

Company and Basis of Presentation [Line Items]

Number of outstanding and unexercised stock options to purchase (in shares)

2,734

Series A Non Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Preferred stock, par value (in dollars per share) | $ / shares

$ 0.0001

$ 0.0001

$ 0.0001

Conversion basis

40

Preferred stock, not automatically converted, outstanding (in shares)

437,037

Issuance of non-voting convertible preferred stock (in shares)

721,452

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

90,992

Preferred stock, outstanding (in shares)

346,045

346,045

346,045

437,037

Series A Non Voting Convertible Preferred Stock | Asset Acquisition

Company and Basis of Presentation [Line Items]

Number of shares transferred as equity interest in asset acquisition (in shares)

364,887

Preferred stock, par value (in dollars per share) | $ / shares

$ 0.0001

Conversion basis

40

Series A Non Voting Convertible Preferred Stock | Spyre Therapeutics, Inc.

Company and Basis of Presentation [Line Items]

Number of shares transferred as equity interest in asset acquisition (in shares)

364,887

Series B Non Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Preferred stock, par value (in dollars per share) | $ / shares

$ 0.0001

$ 0.0001

Conversion basis

40

Preferred stock, not automatically converted, outstanding (in shares)

16,667

16,667

Series B non-voting convertible preferred stock, par value (in dollars per share) | $ / shares

$ 0.0001

Issuance of non-voting convertible preferred stock (in shares)

121,625

271,625

150,000

Preferred stock, outstanding (in shares)

16,667

16,667

Common Stock

Company and Basis of Presentation [Line Items]

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

3,639,680

Private Placement

Company and Basis of Presentation [Line Items]

Gross proceeds received in private placement | $

$ 180,000

Placement agent and other offering costs | $

$ 11,200

10,900

Private Placement | Series A Non Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Number of shares sold in private placement

721,452

Gross proceeds received in private placement | $

$ 210,000

Placement agent and other offering expenses in private placement | $

$ 12,700

Private Placement | Series B Non Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Gross proceeds received in private placement | $

$ 180,000

$ 90,000

Common Stock

Company and Basis of Presentation [Line Items]

Reverse stock split, conversion ratio

0.04

Shares converted (in shares)

10,198,000

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

3,640,000

Common Stock | Conversion Of Series A Non-Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Shares converted (in shares)

25,972,080

Common Stock | Conversion Of Series B Non-Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Shares converted (in shares)

10,198,320

10,198,320

Common Stock | Asset Acquisition

Company and Basis of Presentation [Line Items]

Number of shares transferred as equity interest in asset acquisition (in shares)

517,809

Common stock, par value (in dollars per share) | $ / shares

$ 0.0001

Common Stock | Private Placement

Company and Basis of Presentation [Line Items]

Number of shares of common stock sold (in shares)

6,000,000

Preferred Stock | Series A Non Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Issuance of non-voting convertible preferred stock (in shares)

721,000

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

(91,000)

Preferred stock, outstanding (in shares)

346,000

437,000

346,000

437,000

437,000

Preferred Stock | Series A Non Voting Convertible Preferred Stock | Conversion Of Series A Non-Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Shares converted (in shares)

649,302

Preferred Stock | Series B Non Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Shares converted (in shares)

(255,000)

Issuance of non-voting convertible preferred stock (in shares)

122,000

Preferred stock, outstanding (in shares)

17,000

0

17,000

0

0

Preferred Stock | Series B Non Voting Convertible Preferred Stock | Conversion Of Series B Non-Voting Convertible Preferred Stock

Company and Basis of Presentation [Line Items]

Shares converted (in shares)

254,958

254,958

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Financial Assets:
Total financial assets	$ 424,228	$ 336,953
Liabilities:
Total liabilities	49,089	42,700
U.S. government treasury securities
Financial Assets:
Total financial assets	136,857	32,843
U.S. government agency securities
Financial Assets:
Total financial assets	92,566	16,257
Commercial paper
Financial Assets:
Total financial assets	119,716	104,141
Corporate bonds
Financial Assets:
Total financial assets	31,712	33,064
Parapyre Option Obligation
Liabilities:
Total liabilities	6,889
CVR liability
Liabilities:
Total liabilities	42,200	42,700
Level 1
Financial Assets:
Total financial assets	180,234	183,491
Liabilities:
Total liabilities	0	0
Level 1 | U.S. government treasury securities
Financial Assets:
Total financial assets	136,857	32,843
Level 1 | U.S. government agency securities
Financial Assets:
Total financial assets	0	0
Level 1 | Commercial paper
Financial Assets:
Total financial assets	0	0
Level 1 | Corporate bonds
Financial Assets:
Total financial assets	0	0
Level 1 | Parapyre Option Obligation
Liabilities:
Total liabilities	0
Level 1 | CVR liability
Liabilities:
Total liabilities	0	0
Level 2
Financial Assets:
Total financial assets	243,994	153,462
Liabilities:
Total liabilities	6,889	0
Level 2 | U.S. government treasury securities
Financial Assets:
Total financial assets	0	0
Level 2 | U.S. government agency securities
Financial Assets:
Total financial assets	92,566	16,257
Level 2 | Commercial paper
Financial Assets:
Total financial assets	119,716	104,141
Level 2 | Corporate bonds
Financial Assets:
Total financial assets	31,712	33,064
Level 2 | Parapyre Option Obligation
Liabilities:
Total liabilities	6,889
Level 2 | CVR liability
Liabilities:
Total liabilities	0	0
Level 3
Financial Assets:
Total financial assets	0	0
Liabilities:
Total liabilities	42,200	42,700
Level 3 | U.S. government treasury securities
Financial Assets:
Total financial assets	0	0
Level 3 | U.S. government agency securities
Financial Assets:
Total financial assets	0	0
Level 3 | Commercial paper
Financial Assets:
Total financial assets	0	0
Level 3 | Corporate bonds
Financial Assets:
Total financial assets	0	0
Level 3 | Parapyre Option Obligation
Liabilities:
Total liabilities	0
Level 3 | CVR liability
Liabilities:
Total liabilities	42,200	42,700
Money market funds
Financial Assets:
Total financial assets	43,377	150,648
Money market funds | Level 1
Financial Assets:
Total financial assets	43,377	150,648
Money market funds | Level 2
Financial Assets:
Total financial assets	0	0
Money market funds | Level 3
Financial Assets:
Total financial assets	$ 0	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 22, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Parapyre Option Obligation
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of annual equity grant of options		1%		1%
CVR liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in the fair value of the CVR liability		$ 900		$ 930
Change in fair value of forward contract liability				(930)	$ 0
Forward contract liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of forward contract liability	$ 106,200		$ 164,400		164,400
Change in fair value of forward contract liability		$ 0	$ (58,170)	$ 0	$ (58,170)
Spyre Therapeutics, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset acquisition, stockholder payment period	3 years
Asset acquisition, cash payment, threshold period	1 year
Spyre Therapeutics, Inc. | Series A Non Voting Convertible Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of shares transferred as equity interest in asset acquisition (in shares)	364,887
Outstanding Parapyre warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants to purchase shares (in shares)						684,407
Exercise price per warrant (in dollars per share)						$ 21.52

Fair Value Measurements - Signi

Fair Value Measurements - Significant Inputs used to Estimate the Fair Value of Derivative Liability (Details) - Level 3	Jun. 30, 2024
Minimum | Estimated reimbursement rate compared to reimbursement target | CVR liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability, measurement input	0.81
Minimum | Risk-adjusted discount rates | CVR liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability, measurement input	0.0647
Minimum | CVR liability | Estimated probability of success
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability, measurement input	0.39
Maximum | Estimated reimbursement rate compared to reimbursement target | CVR liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability, measurement input	1
Maximum | Risk-adjusted discount rates | CVR liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability, measurement input	0.0671
Maximum | CVR liability | Estimated probability of success
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability, measurement input	1

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Derivative Liabilities (Details) - CVR liability - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 42,700
Changes in the fair value of the CVR liability	$ 900	930
Payments		(1,430)
Ending balance	$ 42,200	$ 42,200

Cash Equivalents and Marketab_3

Cash Equivalents and Marketable Securities - Estimated Fair Value of Cash Equivalents and Marketable Securities and the Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Cash equivalents, amortized cost	$ 43,377	$ 186,563
Cash equivalents, gross unrealized gains	0	6
Cash equivalents, gross unrealized losses	0	0
Cash equivalents, estimated fair value	43,377	186,569
Marketable securities, amortized cost	381,443	150,101
Marketable securities, gross unrealized gains	81	284
Marketable securities, gross unrealized losses	(673)	(1)
Marketable securities, estimated fair value	380,851	150,384
Money market funds
Debt Securities, Available-for-Sale [Line Items]
Cash equivalents, amortized cost	43,377	150,648
Cash equivalents, gross unrealized gains	0	0
Cash equivalents, gross unrealized losses	0	0
Cash equivalents, estimated fair value	43,377	150,648
Commercial paper
Debt Securities, Available-for-Sale [Line Items]
Cash equivalents, amortized cost		24,950
Cash equivalents, gross unrealized gains		5
Cash equivalents, gross unrealized losses		0
Cash equivalents, estimated fair value		24,955
Marketable securities, amortized cost	119,844	79,124
Marketable securities, gross unrealized gains	3	62
Marketable securities, gross unrealized losses	(131)	0
Marketable securities, estimated fair value	119,716	79,186
Corporate bonds
Debt Securities, Available-for-Sale [Line Items]
Marketable securities, amortized cost	31,797	32,984
Marketable securities, gross unrealized gains	0	81
Marketable securities, gross unrealized losses	(85)	(1)
Marketable securities, estimated fair value	31,712	33,064
U.S. government treasury securities
Debt Securities, Available-for-Sale [Line Items]
Cash equivalents, amortized cost		10,965
Cash equivalents, gross unrealized gains		1
Cash equivalents, gross unrealized losses		0
Cash equivalents, estimated fair value		10,966
Marketable securities, amortized cost	137,061	21,846
Marketable securities, gross unrealized gains	65	31
Marketable securities, gross unrealized losses	(269)	0
Marketable securities, estimated fair value	136,857	21,877
U.S. government agency securities
Debt Securities, Available-for-Sale [Line Items]
Marketable securities, amortized cost	92,741	16,147
Marketable securities, gross unrealized gains	13	110
Marketable securities, gross unrealized losses	(188)	0
Marketable securities, estimated fair value	$ 92,566	$ 16,257

Cash Equivalents and Marketab_4

Cash Equivalents and Marketable Securities - Available-for-Sale Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair Value
Less Than 12 Months	$ 309,201	$ 14,738
12 Months or Longer	0	0
Total, fair value	309,201	14,738
Unrealized Losses
Less Than 12 Months	(673)	(1)
12 Months or Longer	0	0
Total, unrealized losses	(673)	(1)
Commercial paper
Fair Value
Less Than 12 Months	100,124
12 Months or Longer	0
Total, fair value	100,124
Unrealized Losses
Less Than 12 Months	(131)
12 Months or Longer	0
Total, unrealized losses	(131)
Corporate bonds
Fair Value
Less Than 12 Months	31,712	9,907
12 Months or Longer	0	0
Total, fair value	31,712	9,907
Unrealized Losses
Less Than 12 Months	(85)	(1)
12 Months or Longer	0	0
Total, unrealized losses	(85)	(1)
U.S. government treasury securities
Fair Value
Less Than 12 Months	93,432	4,831
12 Months or Longer	0	0
Total, fair value	93,432	4,831
Unrealized Losses
Less Than 12 Months	(269)	0
12 Months or Longer	0	0
Total, unrealized losses	(269)	$ 0
U.S. government agency securities
Fair Value
Less Than 12 Months	83,933
12 Months or Longer	0
Total, fair value	83,933
Unrealized Losses
Less Than 12 Months	(188)
12 Months or Longer	0
Total, unrealized losses	$ (188)

Cash Equivalents and Marketab_5

Cash Equivalents and Marketable Securities - Narrative (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024 USD ($) bank	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) bank	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Cash Equivalents And Marketable Securities [Line Items]
Number of domestic banking institutions (in banks) | bank	2		2
US Government Agencies Debt Securities
Cash Equivalents And Marketable Securities [Line Items]
Debt securities, available-for-sale, allowance for credit loss	$ 0		$ 0		$ 0
Impairment of marketable securities			0		0
Realized gains or losses on marketable securities	0	$ 0	0	$ 0
Accrued interest receivable on available-for-sale debt securities	1,800,000		1,800,000		$ 900,000
U.S. Banking Institution | Maximum
Cash Equivalents And Marketable Securities [Line Items]
Cash, FDIC insured amount	$ 250,000		$ 250,000

Cash Equivalents and Marketab_6

Cash Equivalents and Marketable Securities - Contractual Maturities of Marketable Securities at Estimated Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Cash and Cash Equivalents [Abstract]
Due in one year or less	$ 270,799	$ 115,784
Due in 1 - 2 years	110,052	34,600
Total marketable securities	$ 380,851	$ 150,384

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued compensation	$ 2,664	$ 4,054
Accrued contracted research and development costs	2,269	7,092
Accrued professional and consulting fees	515	1,474
Accrued other	235	488
Total accrued and other current liabilities	$ 5,683	$ 13,108

Asset Acquisition - Narrative (

Asset Acquisition - Narrative (Details) - Spyre Therapeutics, Inc. $ / shares in Units, $ in Millions	Jun. 22, 2023 USD ($) $ / shares shares
Asset Acquisition [Line Items]
Cost to acquire asset | $	$ 113.3
Asset acquisition consideration transferred issuable shares of common stock on an as-converted basis	14,595,480
Spyre 2023 Equity Incentive Plan
Asset Acquisition [Line Items]
Number of outstanding and unexercised stock options to purchase (in shares)	2,734
Series A Non Voting Convertible Preferred Stock
Asset Acquisition [Line Items]
Number of shares transferred as equity interest in asset acquisition (in shares)	364,887
Shares issued, price per share (in dollars per share) | $ / shares	$ 291.08
Common Stock
Asset Acquisition [Line Items]
Number of shares transferred as equity interest in asset acquisition (in shares)	517,809
Shares issued, price per share (in dollars per share) | $ / shares	$ 7.277

Asset Acquisition - Asset Acqui

Asset Acquisition - Asset Acquisition Cost (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 22, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Asset Acquisition [Line Items]
Acquired in-process research and development		$ 0	$ 130,486	$ 0	$ 130,486
Cash acquired				$ 0	$ 3,035
Spyre Therapeutics, Inc.
Asset Acquisition [Line Items]
Consideration transferred in Series A Preferred Stock and Common Stock	$ 110,000
Transaction costs incurred by Pre-Merger Spyre	3,200
Fair value of Parapyre Option Obligation assumed by Pre-Merger Spyre	100
Acquired in-process research and development	130,500
Cash acquired	3,000
Assumed liabilities	(20,200)
Total cost to acquire asset	$ 113,300

Licensing Agreements (Details)

Licensing Agreements (Details) - Related Party - USD ($) $ in Millions			3 Months Ended		6 Months Ended
	Dec. 14, 2023	Jul. 12, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Paragon Agreement
Related Party Transaction [Line Items]
Campaign timeline, minimum term					5 years
Royalty step-down percentage			33%		33%
Royalty term expiration period					12 years
Termination notice period					60 days
Sublicensing fee			$ 0.1		$ 0.1
Milestone expense recognized			5.5	$ 0	5.5	$ 0
Milestone payments			3		3
Milestone payments, outstanding and payable			$ 2.5		2.5
SPY001 License Agreement
Related Party Transaction [Line Items]
Nomination fee		$ 1.5
First milestone payment		2.5
SPY001 License Agreement | Maximum
Related Party Transaction [Line Items]
Contingent obligation based on milestones		$ 22
SPY002 License Agreement
Related Party Transaction [Line Items]
Nomination fee	$ 1.5
First milestone payment	2.5
SPY002 License Agreement | Maximum
Related Party Transaction [Line Items]
Contingent obligation based on milestones	$ 22
Sublicensing fee					$ 20

Related Party Transactions - Na

Related Party Transactions - Narrative (Details)		3 Months Ended		6 Months Ended
	Nov. 22, 2023 $ / shares shares	Jun. 30, 2024 USD ($) seat shares	Jun. 30, 2023 USD ($) shares	Jun. 30, 2024 USD ($) seat shares	Jun. 30, 2023 USD ($) shares	Apr. 01, 2024	Mar. 31, 2024
Related Party Transaction [Line Items]
Stock-based compensation		$ 8,700,000	$ 1,900,000	$ 22,517,000	$ 3,620,000
Options granted (in shares) | shares		387,695	2,536,697	1,432,353	2,714,317
Stock-based compensation expense		$ 8,682,000	$ 1,911,000	$ 22,517,000	$ 3,620,000
Related Party
Related Party Transaction [Line Items]
Development cost reduction, percent						50%
Development cost reimbursement, percent							50%
Related Party | Paragon Agreement
Related Party Transaction [Line Items]
Number of board seats held by related party | seat		2		2
Amount of related party transaction		$ 11,300,000		$ 29,500,000
Stock-based compensation		1,500,000		6,900,000
Receivable		$ 5,900,000		$ 5,900,000
Common stock, shares outstanding, percentage available to purchase on a diluted basis		1%		1%
Related Party | Subsequent to Asset Acquisition
Related Party Transaction [Line Items]
Amount of related party transaction		$ 9,700,000		$ 26,800,000
Related Party | Consulting Agreement
Related Party Transaction [Line Items]
Options granted (in shares) | shares	477,000
Exercise price (in dollars per share) | $ / shares	$ 10.39
Vesting period	36 months
Stock-based compensation expense		$ 200,000	$ 0	$ 500,000	$ 0
Related Party | Consulting Agreement | Share-Based Payment Arrangement, Tranche One
Related Party Transaction [Line Items]
Vesting percentage	25%
Vesting period	1 year
Paragon Therapeutics Inc | Maximum | Related Party | Paragon Agreement
Related Party Transaction [Line Items]
Percentage of ownership by noncontrolling owner		5%		5%
Fairmount Funds Management LLC | Minimum | Related Party | Paragon Agreement
Related Party Transaction [Line Items]
Percentage of ownership by noncontrolling owner		5%		5%
Percentage of ownership held in third party		5%		5%

Related Party Transactions - Ex

Related Party Transactions - Expenses related to Related Party which were Settled in Cash (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Related Party Transaction [Line Items]
Research and development	[1]	$ 32,636	$ 17,386	$ 67,564	$ 31,162
Related Party
Related Party Transaction [Line Items]
Research and development		9,400	1,400	26,500	1,400
Paragon and License Agreement | Related Party
Related Party Transaction [Line Items]
Research and development		7,900	1,200	19,600	1,200
Paragon Agreement | Related Party
Related Party Transaction [Line Items]
Research and development		2,300	1,200	14,000	1,200
License Agreement | Related Party
Related Party Transaction [Line Items]
Research and development		$ 5,600	$ 0	$ 5,600	$ 0
[1] Includes $9.4 million and $26.5 million in related party expenses for the three and six months ended June 30, 2024, respectively, and $1.4 million related party expenses for the three and six months ended June 30, 2023.

Related Party Transactions - Re

Related Party Transactions - Related Party Accounts Payable (Details) - Related Party - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Related Party Transaction [Line Items]
Total related party accounts payable	$ 10.6	$ 16.6
Paragon Agreement
Related Party Transaction [Line Items]
Total related party accounts payable	1.2	16.6
Parapyre warrants liability
Related Party Transaction [Line Items]
Total related party accounts payable	6.9	0
License Agreements development milestone liability (see Note 7)
Related Party Transaction [Line Items]
Total related party accounts payable	$ 2.5	$ 0

Convertible Preferred Stock a_2

Convertible Preferred Stock and Stockholders' Equity - Narrative (Details) $ / shares in Units, $ in Thousands

3 Months Ended

6 Months Ended

40 Months Ended

May 14, 2024 shares

Apr. 23, 2024 shares

Mar. 20, 2024 USD ($) shares

Mar. 18, 2024 shares

Dec. 11, 2023 USD ($) shares

Nov. 21, 2023 shares

Jul. 07, 2023 shares

Jun. 26, 2023 USD ($) shares

Jun. 22, 2023

Jun. 30, 2024 shares

Mar. 31, 2024 USD ($) shares

Jun. 30, 2023 USD ($) shares

Jun. 30, 2024 shares

May 31, 2022 $ / shares

Apr. 25, 2024 shares

Dec. 31, 2023 $ / shares shares

Nov. 22, 2023 shares

Common Stock

Class of Stock [Line Items]

Shares converted (in shares)

10,198,000

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

3,640,000

Conversion Of Series A Non-Voting Convertible Preferred Stock | Common Stock

Class of Stock [Line Items]

Shares converted (in shares)

25,972,080

Conversion Of Series B Non-Voting Convertible Preferred Stock | Common Stock

Class of Stock [Line Items]

Shares converted (in shares)

10,198,320

10,198,320

Private Placement

Class of Stock [Line Items]

Gross proceeds received in private placement | $

$ 180,000

Series A Non Voting Convertible Preferred Stock

Class of Stock [Line Items]

Preferred stock issued and outstanding percentage

30%

Issuance of non-voting convertible preferred stock (in shares)

721,452

Issuance of Series A/B non-voting convertible preferred stock in connection with private placement, net of financing costs | $

$ 197,300

Conversion basis

40

Preferred stock, not automatically converted, outstanding (in shares)

437,037

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

90,992

Preferred stock, outstanding (in shares)

346,045

346,045

346,045

437,037

Series A Non Voting Convertible Preferred Stock | Preferred Stock

Class of Stock [Line Items]

Issuance of non-voting convertible preferred stock (in shares)

721,000

Issuance of Series A/B non-voting convertible preferred stock in connection with private placement, net of financing costs | $

$ 197,323

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

(91,000)

Preferred stock, outstanding (in shares)

346,000

437,000

346,000

437,000

Series A Non Voting Convertible Preferred Stock | Conversion Of Series A Non-Voting Convertible Preferred Stock | Preferred Stock

Class of Stock [Line Items]

Shares converted (in shares)

649,302

Series A Non Voting Convertible Preferred Stock | Asset Acquisition

Class of Stock [Line Items]

Number of shares transferred as equity interest in asset acquisition (in shares)

364,887

Series A Non Voting Convertible Preferred Stock | Private Placement

Class of Stock [Line Items]

Number of shares sold in private placement

721,452

Gross proceeds received in private placement | $

$ 210,000

Common Stock

Class of Stock [Line Items]

Exchange of Series A non-voting convertible preferred stock into common stock (in shares)

3,639,680

Series B Non Voting Convertible Preferred Stock

Class of Stock [Line Items]

Issuance of non-voting convertible preferred stock (in shares)

121,625

271,625

150,000

Conversion basis

40

Preferred stock, not automatically converted, outstanding (in shares)

16,667

16,667

Preferred stock, outstanding (in shares)

16,667

16,667

Series B Non Voting Convertible Preferred Stock | Preferred Stock

Class of Stock [Line Items]

Issuance of non-voting convertible preferred stock (in shares)

122,000

Issuance of Series A/B non-voting convertible preferred stock in connection with private placement, net of financing costs | $

$ 168,850

Shares converted (in shares)

(255,000)

Preferred stock, outstanding (in shares)

17,000

0

17,000

0

Series B Non Voting Convertible Preferred Stock | Conversion Of Series B Non-Voting Convertible Preferred Stock | Preferred Stock

Class of Stock [Line Items]

Shares converted (in shares)

254,958

254,958

Series B Non Voting Convertible Preferred Stock | Private Placement

Class of Stock [Line Items]

Gross proceeds received in private placement | $

$ 180,000

$ 90,000

Maximum | Series A Non Voting Convertible Preferred Stock

Class of Stock [Line Items]

Beneficially holders owned percentage

19.90%

Maximum | Series B Non Voting Convertible Preferred Stock

Class of Stock [Line Items]

Beneficial holders owned percentage

19.90%

Minimum | Series A Non Voting Convertible Preferred Stock

Class of Stock [Line Items]

Beneficially holders owned percentage

0%

Minimum | Series B Non Voting Convertible Preferred Stock

Class of Stock [Line Items]

Beneficial holders owned percentage

0%

Pre-Funded Warrants

Class of Stock [Line Items]

Exercise price per warrant (in dollars per share) | $ / shares

$ 0.0025

Maximum ownership percentage of common stock shares for outstanding warrants to be exercised

4.99%

Ownership percentage for outstanding warrants to purchase shares of common stock to be exercised to certain holders

9.99%

Revised ownership percentage, period to take effect after notice

61 days

Number of shares sold in private placement

0

0

Pre-Funded Warrants | Maximum

Class of Stock [Line Items]

Maximum ownership percentage of common stock shares for outstanding warrants to be exercised

19.99%

Outstanding Parapyre warrants

Class of Stock [Line Items]

Exercise price per warrant (in dollars per share) | $ / shares

$ 21.52

Maximum ownership percentage of common stock shares for outstanding warrants to be exercised

4.99%

Warrants to purchase shares (in shares)

684,407

Number of warrants exercised (in shares)

0

0

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 22, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2016	Jan. 01, 2024	Jan. 01, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation		$ 8,700	$ 1,900	$ 22,517	$ 3,620
Two Thousand And Fifteen And Two Thousand And Sixteen Equity Incentive Plan And Two Thousand And Eighteen Equity Inducement Plan | Service Based Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vest period grant date				4 years
Share-based payment award, term				10 years
Two Thousand And Fifteen Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares subject to options outstanding (in shares)				3,029
2016 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual percentage of additional shares						5%
Additional number of shares available for issuance (in shares)							3,023,650	104,561
Common stock available for future issuance (in shares)		7,336,181		7,336,181
Outstanding option awards (in shares)		3,024,766		3,024,766
2018 Equity Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for future issuance (in shares)		6,028,000		6,028,000
Outstanding option awards (in shares)		5,682,341		5,682,341
Spyre 2023 Equity Incentive Plan | Asset Acquisition
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding and unexercised stock options to purchase (in shares)	2,734
Parapyre Option Obligation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Pro-rated estimated fair value of options				$ 6,900
Stock-based compensation		$ 1,500	$ 200	6,900	$ 200
Unamortized expense		$ 7,000		$ 7,000
2016 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued (in shares)				2,330	1,793

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Awards Granted (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-Based Payment Arrangement [Abstract]
Grants (in shares)	387,695	2,536,697	1,432,353	2,714,317
Weighted Average Grant Date Fair Value (in dollars per share)	$ 36.42	$ 7.50	$ 29.19	$ 7.75

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 8,682	$ 1,911	$ 22,517	$ 3,620
Stock-based compensation	8,700	1,900	22,517	3,620
Aeglea Employees and Directors
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	700	1,800	3,800	3,500
Parapyre Option Obligation
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	1,500	200	6,900	200
Research and Development Expense
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	3,451	394	10,308	1,171
General and administrative
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 5,231	$ 1,517	$ 12,209	$ 2,449

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions used to Estimate the Fair Value of Stock Options Granted (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Stock Options Granted
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term (in years)	5 years 11 months 1 day	6 years 10 days	6 years	6 years 10 days
Expected volatility	104%	117%	105%	115%
Risk-free interest	4.35%	3.98%	4.01%	3.99%
Dividend yield	0%	0%	0%	0%
2016 ESPP
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term (in years)			6 months	5 months 26 days
Expected volatility			98%	181%
Risk-free interest			5.31%	4.99%
Dividend yield			0%	0%

Legacy Strategic License Agre_2

Legacy Strategic License Agreements - Narrative (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jul. 27, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenue		$ 0	$ 688,000	$ 0	$ 886,000
Contract assets		0		0		$ 0
Contract liabilities		0		0		$ 0
Immedica Pharma AB
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenue		$ 0		$ 0
Immedica Pharma AB | Peace Phase 3 Trial and Drug Supply
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenue			$ 700,000		$ 900,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Global Rights To Pegzilarginase
Research And Development Arrangement Contract To Perform For Others [Line Items]
Proceeds from sale of intangible assets	$ 15,000,000
Contingent consideration	$ 100,000,000

Net Loss Per Share - Weighted-A

Net Loss Per Share - Weighted-Average Equity Instruments Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,010,436	654,527	4,526,643	557,515
Unvested restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	79,870	0	71,368	381
Outstanding Parapyre warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	684,407	0	684,407	0
Series A Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	14,801,716	0	16,141,598	0
Series B Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	351,655	0	175,828	0

Net Loss Per Share - Reconcilia

Net Loss Per Share - Reconciliation of Basic and Diluted Net Loss Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Weighted average common shares (in shares)	45,214,616	2,711,439	40,738,639	2,663,408
Weighted average pre-funded warrants (in shares)	101,648	1,111,166	175,824	1,133,291
Total basic weighed average shares (in shares)	45,316,264	3,822,605	40,914,463	3,796,699
Total diluted weighed average shares (in shares)	45,316,264	3,822,605	40,914,463	3,796,699

Restructuring Charges - Narrati

Restructuring Charges - Narrative (Details) - USD ($)		1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Apr. 30, 2023	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Aug. 07, 2023
Restructuring Cost and Reserve [Line Items]
Employee workforce, termination percentage		83%	83%
Cash severance payments and other employee-related costs			$ 6,400,000		$ 6,400,000
Non-cash stock-based compensation expense related to accelerated vesting of stock-based awards					1,000,000
Total consideration from disposal of long lived assets	$ 500,000		500,000		500,000
Loss on disposal of long-lived assets				$ 0	$ 915,000
Lease asset impairment	900,000
Impairment on leasehold improvements	$ 1,700,000
Termination fee amount							$ 2,000,000
Restructuring costs outstanding and unpaid				$ 0		$ 1,100,000
Research and Development Expense
Restructuring Cost and Reserve [Line Items]
Loss on disposal of long-lived assets			700,000
General and administrative
Restructuring Cost and Reserve [Line Items]
Loss on disposal of long-lived assets			$ 200,000

Restructuring Charges - Charges

Restructuring Charges - Charges Related to the Restructuring Activities (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Restructuring Cost and Reserve [Line Items]
Severance Related Expenses			$ 6,400		$ 6,400
Stock-based compensation expense		$ 8,682	1,911	$ 22,517	3,620
Loss on Disposal of Long Lived Assets				0	915
Lease Asset Impairment	$ 900
Research and Development Expense
Restructuring Cost and Reserve [Line Items]
Stock-based compensation expense		3,451	394	10,308	1,171
Loss on Disposal of Long Lived Assets			700
General and administrative
Restructuring Cost and Reserve [Line Items]
Stock-based compensation expense		$ 5,231	1,517	$ 12,209	$ 2,449
Loss on Disposal of Long Lived Assets			200
Restructuring Activities
Restructuring Cost and Reserve [Line Items]
Severance Related Expenses			6,448
Stock-based compensation expense			993
Loss on Disposal of Long Lived Assets			931
Lease Asset Impairment			2,580
Total Restructuring Costs			10,952
Restructuring Activities | Research and Development Expense
Restructuring Cost and Reserve [Line Items]
Severance Related Expenses			3,182
Stock-based compensation expense			123
Loss on Disposal of Long Lived Assets			749
Lease Asset Impairment			1,405
Total Restructuring Costs			5,459
Restructuring Activities | General and administrative
Restructuring Cost and Reserve [Line Items]
Severance Related Expenses			3,266
Stock-based compensation expense			870
Loss on Disposal of Long Lived Assets			182
Lease Asset Impairment			1,175
Total Restructuring Costs			$ 5,493