Spyre Therapeutics (SYRE) 10-Q 11 Aug 23 2023 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2023	Aug. 04, 2023
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q2
Trading Symbol	AGLE
Security Exchange Name	NASDAQ
Entity Registrant Name	AEGLEA BIOTHERAPEUTICS, INC.
Entity Central Index Key	0001636282
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity File Number	001-37722
Entity Tax Identification Number	46-4312787
Entity Address, Address Line One	221 Crescent Street
Entity Address, Address Line Two	Building 17
Entity Address, Address Line Three	Suite 102B
Entity Address, City or Town	Waltham
Title of 12(b) Security	Common Stock, $0.0001 Par Value Per Share
Entity Address, Postal Zip Code	02453
City Area Code	617
Local Phone Number	651-5940
Entity Address, State or Province	MA
Entity Incorporation, State or Country Code	DE
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		101,192,921
Former Address
Document Information [Line Items]
Entity Address, Address Line One	805 Las Cimas Parkway
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Austin
Entity Address, Postal Zip Code	78746
Entity Address, State or Province	TX

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
CURRENT ASSETS
Cash and cash equivalents	$ 235,358	$ 34,863
Marketable securities	0	20,848
Development receivables	1,646	375
Prepaid expenses and other current assets	2,882	6,172
Total current assets	239,886	62,258
Restricted cash	1,317	1,553
Property and equipment, net	0	3,220
Operating lease right-of-use assets	2,316	3,430
Other non-current assets	10	683
TOTAL ASSETS	243,529	71,144
CURRENT LIABILITIES
Accounts payable	2,854	677
Forward contract liability	164,382	0
CVR liability	10,500	0
Operating lease liabilities	4,331	625
Deferred revenue	930	517
Accrued and other current liabilities	28,427	12,837
Related party accounts payable	20,810	0
Total current liabilities	232,234	14,656
Non-current CVR liability	19,000	0
Non-current operating lease liabilities	0	4,004
Deferred revenue, net of current portion	2,341	2,179
TOTAL LIABILITIES	253,575	20,839
Commitments and Contingencies
STOCKHOLDERS' (DEFICIT) EQUITY
Preferred stock, $0.0001 par value; 8,913,659 shares and 10,000,000 authorized as of June 30, 2023 and December 31, 2022; no shares issued and outstanding as of June 30, 2023 and December 31, 2022	0	0
Common stock, $0.0001 par value; 500,000,000 shares authorized as of June 30, 2023 and December 31, 2022; 81,001,676 shares and 65,350,343 shares issued and outstanding as of June 30, 2023 and December 31, 2022, respectively	6	6
Additional paid-in capital	453,741	475,971
Accumulated other comprehensive income (loss)	11	(48)
Accumulated deficit	(661,127)	(425,624)
TOTAL STOCKHOLDERS’ EQUITY	(207,369)	50,305
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	243,529	71,144
Series A Non Voting Convertible Preferred Stock [Member]
CURRENT LIABILITIES
Series A non-voting convertible preferred stock, $0.0001 par value; 1,086,341 and no shares authorized as of June 30, 2023 and December 31, 2022, respectively; 721,452 and no shares issued and outstanding as of June 30, 2023 and December 31, 2022, respectively	$ 197,323	$ 0

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Jun. 30, 2023	Dec. 31, 2022
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	8,913,659	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	81,001,676	65,350,343
Common stock, shares outstanding	81,001,676	65,350,343
Series A Non Voting Convertible Preferred Stock [Member]
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	1,086,341	0
Convertible preferred stock, shares issued	721,452	0
Convertible preferred stock, shares outstanding	721,452	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenue:
Total revenue		$ 688	$ 625	$ 886	$ 1,987
Operating expenses:
Research and development	[1]	17,386	15,373	31,162	32,351
General and administrative		12,062	7,675	17,290	16,500
Acquired in-process research and development		130,486	0	130,486	0
Total operating expenses		159,934	23,048	178,938	48,851
Loss from operations		(159,246)	(22,423)	(178,052)	(46,864)
Other income (expense):
Interest income		350	104	770	139
Change in fair value of forward contract liability		(58,170)	0	(58,170)	0
Other income (expense), net		(8)	5	(80)	1
Total other (expense) income		(57,828)	109	(57,480)	140
Loss before income tax expense		(217,074)	(22,314)	(235,532)	(46,724)
Income tax (expense) benefit		(7)	(9)	29	(35)
Net loss		$ (217,081)	$ (22,323)	$ (235,503)	$ (46,759)
Net loss per share, basic		$ (2.27)	$ (0.27)	$ (2.48)	$ (0.63)
Net loss per share, diluted		$ (2.27)	$ (0.27)	$ (2.48)	$ (0.63)
Weighted-average common shares outstanding, basic		95,565,118	82,209,032	94,917,487	73,650,146
Weighted-average common shares outstanding, diluted		95,565,118	82,209,032	94,917,487	73,650,146
Development Fee and Royalty [Member]
Revenue:
Total revenue		$ 688	$ 625	$ 886	$ 1,987
[1] Includes $ 1.4 million and no related party expense, for the three and six months ended June 30, 2023 and 2022, respectively.

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations (Unaudited) (Parenthetical) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Research and development, related party expense	$ 1,400,000	$ 0	$ 1,400,000	$ 0

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (217,081)	$ (22,323)	$ (235,503)	$ (46,759)
Other comprehensive income (loss):
Foreign currency translation adjustment	18	(36)	28	(49)
Unrealized (loss) gain on marketable securities	(1)	(31)	31	(151)
Total comprehensive loss	$ (217,064)	$ (22,390)	$ (235,444)	$ (46,959)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders' (Deficit) Equity (Unaudited) - USD ($) shares in Thousands	Total	Preferred Stock Series A Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Dec. 31, 2021	$ 83,941,000		$ 5,000	$ 425,765,000	$ (20,000)	$ (341,809,000)
Balances (in shares) at Dec. 31, 2021			49,355
Issuance of common stock in connection with employee stock purchase plan	184,000			184,000
Issuance of common stock in connection with employee stock purchase plan (in shares)			65
Stock-based compensation expense	2,101,000			2,101,000
Foreign currency translation adjustment	(13,000)				(13,000)
Unrealized gain (loss) on marketable securities	(120,000)				(120,000)
Net loss	(24,436,000)					(24,436,000)
Balances at Mar. 31, 2022	61,657,000		$ 5,000	428,050,000	(153,000)	(366,245,000)
Balances (in shares) at Mar. 31, 2022			49,420
Balances at Dec. 31, 2021	83,941,000		$ 5,000	425,765,000	(20,000)	(341,809,000)
Balances (in shares) at Dec. 31, 2021			49,355
Foreign currency translation adjustment	(49,000)
Unrealized gain (loss) on marketable securities	(151,000)
Net loss	(46,759,000)
Balances at Jun. 30, 2022	84,157,000		$ 6,000	472,939,000	(220,000)	(388,568,000)
Balances (in shares) at Jun. 30, 2022			61,173
Balances at Mar. 31, 2022	61,657,000		$ 5,000	428,050,000	(153,000)	(366,245,000)
Balances (in shares) at Mar. 31, 2022			49,420
Issuance of common stock and pre-funded warrants in connection with registered direct offering, net of offering costs	42,873,000		$ 1,000	42,872,000
Issuance of common stock and pre-funded warrants in connection with registered direct offering, net of offering costs (in shares)			10,753
Issuance of common stock in connection with exercise of pre-funded warrants (in shares)			1,000
Stock-based compensation expense	2,017,000			2,017,000
Foreign currency translation adjustment	(36,000)				(36,000)
Unrealized gain (loss) on marketable securities	(31,000)				(31,000)
Net loss	(22,323,000)					(22,323,000)
Balances at Jun. 30, 2022	84,157,000		$ 6,000	472,939,000	(220,000)	(388,568,000)
Balances (in shares) at Jun. 30, 2022			61,173
Balances at Dec. 31, 2022	50,305,000		$ 6,000	475,971,000	(48,000)	(425,624,000)
Balances (in shares) at Dec. 31, 2022			65,350
Issuance of common stock in connection with employee stock purchase plan	18,000			18,000
Issuance of common stock in connection with employee stock purchase plan (in shares)			45
Stock-based compensation expense	1,709,000			1,709,000
Foreign currency translation adjustment	10,000				10,000
Unrealized gain (loss) on marketable securities	32,000				32,000
Net loss	(18,422,000)					(18,422,000)
Balances at Mar. 31, 2023	33,652,000		$ 6,000	477,698,000	(6,000)	(444,046,000)
Balances (in shares) at Mar. 31, 2023			65,395
Balances at Dec. 31, 2022	50,305,000		$ 6,000	475,971,000	(48,000)	(425,624,000)
Balances (in shares) at Dec. 31, 2022			65,350
Foreign currency translation adjustment	28,000
Unrealized gain (loss) on marketable securities	31,000
Net loss	(235,503,000)
Balances at Jun. 30, 2023	(207,369,000)		$ 6,000	453,741,000	11,000	(661,127,000)
Balances (in shares) at Jun. 30, 2023			81,002
Balances at Jun. 30, 2023		$ 197,323,000
Balances (in shares) at Jun. 30, 2023		721
Balances at Mar. 31, 2023	33,652,000		$ 6,000	477,698,000	(6,000)	(444,046,000)
Balances (in shares) at Mar. 31, 2023			65,395
Issuance of Series A non-voting convertible preferred stock in connection with private placement, net of financing costs		$ 197,323,000
Issuance of Series A non-voting convertible preferred stock in connection with private placement, net of financing costs, (in shares)		721
Issuance of common stock forward in connection with the asset acquisition of Spyre	3,768,000			3,768,000
Issuance of common stock in connection with exercise of pre-funded warrants (in shares)			15,607
CVR distribution to common stockholders	(29,500,000)			(29,500,000)
Stock-based compensation expense	1,775,000			1,775,000
Foreign currency translation adjustment	18,000				18,000
Unrealized gain (loss) on marketable securities	(1,000)				(1,000)
Net loss	(217,081,000)					(217,081,000)
Balances at Jun. 30, 2023	$ (207,369,000)		$ 6,000	$ 453,741,000	$ 11,000	$ (661,127,000)
Balances (in shares) at Jun. 30, 2023			81,002
Balances at Jun. 30, 2023		$ 197,323,000
Balances (in shares) at Jun. 30, 2023		721

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (235,503)	$ (46,759)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	744	781
Stock-based compensation	3,620	4,118
Acquired in-process research and development	130,486	0
Change in fair value of forward contract liability	58,170	0
Lease ROU asset and leasehold improvement impairment loss	2,580
Loss on disposal of long-lived assets	915
Amortization of operating lease assets	220	191
Purchase net premium on marketable securities		239
Net amortization of premium (accretion of discount) on marketable securities	(123)	(23)
Other	6	(7)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	3,368	(2,419)
Accounts payable	2,045	(1,352)
Deferred revenue	575	(914)
Development receivables	(1,271)	336
Operating lease liabilities	(298)	(250)
Accrued and other liabilities	189	(877)
Net cash used in operating activities	(34,277)	(46,936)
CASH FLOWS FROM INVESTING ACTIVITIES
Cash assumed from asset acquisition of Spyre	3,035
Purchases of property and equipment		(37)
Proceeds from sale of property and equipment	475
Purchases of marketable securities		(27,750)
Proceeds from maturities and sales of marketable securities	21,000	54,296
Net cash provided by investing activities	24,510	26,509
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of Series A non-voting convertible preferred stock, gross in connection with private placement	210,000
Proceeds from issuance of common stock and pre-funded warrants in registered direct offering, net of offering costs		42,979
Proceeds from employee stock plan purchases and stock option exercises	18	184
Principal payments on finance lease obligation	(16)	(347)
Net cash provided by financing activities	210,002	42,816
Effect of exchange rate on cash, cash equivalents, and restricted cash	24	(95)
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	200,259	22,294
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	36,416	16,980
End of period	236,675	$ 39,274
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Unpaid direct transaction costs related to the asset acquisition of Spyre	2,067
Unpaid amounts related to issuance of Series A non-voting convertible preferred stock in connection with private placement	$ 12,677

The Company and Basis of Presen

The Company and Basis of Presentation	6 Months Ended
	Jun. 30, 2023
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company and Basis of Presentation	1. The Company and Basis of Presentation Aeglea BioTherapeutics, Inc. (“Aeglea” or the “Company”) is a preclinical 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. The Company operates in one segment and has its principal offices in Waltham, Massachusetts. On April 12, 2023, based on the review of the inconclusive interim results from our 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 ("Spyre"), as disclosed in Note 7 and 8, 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 ("Paragon"). The transaction was structured as a stock-for-stock transaction pursuant to which all of Spyre's outstanding equity interests were exchanged based on a fixed exchange ratio of 13.73622 to 1 for consideration from Aeglea of 12,945,385 shares of 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 1,000 to 1 basis) in addition to the assumption of outstanding and unexercised stock options to purchase 68,365 shares of common stock from the Amended and Restated Spyre 2023 Equity Incentive Plan (the "Asset Acquisition"). The Aeglea common stock and Aeglea Series A Preferred Stock related to the Asset Acquisition were issued to the Spyre stockholders on July 7, 2023. For additional information, see Note 7 and 8. In connection with the Asset Acquisition, on June 26, 2023, the Company completed a private placement of shares of Series A Preferred Stock (the “PIPE”) to a group of investors (the “Investors”). The Company sold an aggregate of 721,452 shares of Series A Preferred Stock (the “PIPE Securities”) for an aggregate purchase price of approximately $ 210.0 million before deducting approximately $ 12.7 million placement agent and other offering expenses. For additional information, see Note 8. In connection with the Asset Acquisition, a non-transferable contingent value right ("CVR") was distributed to Aeglea stockholders of record 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 Spyre or Investors in the Transactions. Holders of the CVRs will be entitled to receive cash payments from proceeds received by Aeglea for a three-year period, if any, related to the disposition or monetization of its legacy assets for a period of one-year following the closing of the Asset Acquisition. For additional information see Note 3. Liquidity As of June 30, 2023, the Company had accumulated deficit of $ 661.1 million, and cash and cash equivalents of $ 235.4 million, which includes proceeds from the PIPE. The Company has not generated any product revenues and has not achieved profitable operations. There is no assurance that profitable operations will ever be achieved, and, if achieved, could be sustained on a continuing basis. In addition, development activities, clinical and nonclinical testing, and commercialization of the Company’s product candidates will require significant additional financing before a commercial drug can be produced and marketed. The Company is subject to a number of risks similar to other life science companies, including, but not limited to, risks related to the successful discovery, development, and commercialization of product candidates, raising additional capital, development of competing drugs and therapies, protection of proprietary technology and market acceptance of the Company’s product candidates. As a result of these and other factors and the related uncertainties, there can be no assurance of the Company’s future success. In April 2023, the Board of Directors approved a restructuring of the Company’s workforce pursuant to which the Company’s workforce was reduced by approximately 83 %, retaining approximately 10 employees. Additionally, the Company announced interim results from its ongoing Phase 1/2 clinical trial of pegtarviliase for the treatment of classical homocystinuria. Following a review of the interim results and other business considerations, the Company explored strategic alternatives with the goal of maximizing stockholder value, including possible business combinations and/or a divestiture of the Company’s clinical programs. On June 22, 2023, the Company acquired, in accordance with the terms of the Acquisition Agreement, the net assets of Spyre, as disclosed in Note 7 and 8. Additionally, the Company completed the PIPE. In accordance with ASC 205-40, Going Concern, the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the financial statements are issued. If our stockholders do not timely approve the conversion of our Series A Preferred Stock, then the holders of our Series A Preferred Stock may be entitled to require us to settle their shares of Series A Preferred Stock for cash at a price per share equal to the fair value of the Series A Preferred Stock, as described in our Certificate of Designation relating to the Series A Preferred Stock (see Note 9). The cash redemption is not in our control and raises substantial doubt about our ability to continue as a going concern. The accompanying condensed consolidated financial statements assume the Company will continue as a going concern through the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Unaudited Interim Financial Information The interim condensed consolidated financial statements included in this document 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, 2023, and its results of operations for the three and six months ended June 30, 2023 and 2022, changes in convertible preferred stock and stockholders’ (deficit) equity for the three and six months ended June 30, 2023 and 2022, and cash flows for the six months ended June 30, 2023 and 2022 . The results of operations for the three and six months ended June 30, 2023, are not necessarily indicative of the results to be expected for the year ending December 31, 2023 or for any other future annual or interim period. The December 31, 2022 balance sheet was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States (“U.S. GAAP”). 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, 2022 (the "Annual Report") as filed with the Securities and Exchange Commission ("SEC").

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. 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. Convertible Preferred Stock Issued through PIPE The Company records shares of convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The Company has applied the guidance in ASC 480-10-S99-3A, SEC Staff Announcement: Classification and Measurement of Redeemable Securities, and has therefore classified the Series A Preferred Stock outside of stockholders’ (deficit) equity because, if conversion to common stock is not approved by the stockholders, the Series A Preferred Stock will be redeemable at the option of the holders for cash equal to the closing price of the common stock on the last trading day prior to the holder’s redemption request. The Company determined that the conversion and redemption are outside of the Company’s control. Additionally, the Company determined the conversion and redemption features did not require bifurcation as derivatives. Acquisitions The Company evaluates acquisitions of assets and other similar transactions to assess whether or not the transaction should be accounted for as a business combination or asset acquisition by first applying a screen test to determine whether substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. If so, the transaction is accounted for as an asset acquisition. If not, further determination is required as to whether or not the Company has acquired inputs and processes that have the ability to create outputs, which would meet the definition of a business. Significant judgment is required in the application of the screen test to determine whether an acquisition is a business combination or an acquisition of assets. Acquisitions meeting the definition of business combinations are accounted for using the acquisition method of accounting, which requires that the purchase price be allocated to the net assets acquired at their respective fair values. In a business combination, any excess of the purchase price over the estimated fair values of the net assets acquired is recorded as goodwill. The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the assets, which includes transaction costs. Goodwill is not recognized in asset acquisitions. When a transaction accounted for as an asset acquisition includes an in-process research and development (“IPR&D”) asset, the IPR&D asset is only capitalized if it has an alternative future use other than in a particular research and development project. Otherwise, the cost allocated to acquire an IPR&D with no alternative future use is charged to expense at the acquisition date. Contingent Value Rights The Company evaluates its contracts to determine if those contracts qualify as derivatives under ASC 815, Derivatives and Hedging . For derivative financial instruments that are accounted for as liabilities, the derivative instrument is initially recorded at its fair value and is then re-valued at each reporting date. Any changes in fair value are recorded as other income or expense for each reporting period. Derivative instrument liabilities are classified in the balance sheet as current or non-current based on whether or not net-cash settlement of the derivative instrument is probable within the next 12 months from the balance sheet date. The Company determined that certain contingent payments under the CVR Agreement qualified as derivatives under ASC 815, and as such, were recorded as a liability on the balance sheet as of June 30, 2023. The Company applies a scenario-based method and weights them based on the possible achievement of certain milestones. 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. This fair value measurement is based on significant inputs not observable in the market and thus represents a Level 3 measurement as defined in ASC 820, Fair Value Measurement . The key assumptions used include the discount rate, probability of regulatory success, and reimbursement rates from certain government agencies. The estimated value of the CVR consideration is based upon available information and certain assumptions which the Company's management believes are reasonable under the circumstances. The ultimate payout under the CVRs may differ materially from the assumptions used in determining the fair value of the CVR consideration. This value is then remeasured for future expected payout as well as the increase in fair value due to the time value of money. These gains or losses, if any, are recognized in the consolidated statements of operations and comprehensive loss. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets, liabilities, and equity and the amount of revenues and expenses. Actual results could differ significantly from those estimates. The most significant estimates and assumptions that management considers in the preparation of the Company's financial statements relate to accrued research and development costs; the valuation of consideration transferred in acquiring IPR&D; the discount rate, probabilities of success, and timing of estimated cash flows in the valuation of the CVR liability; inputs used in the Black-Scholes model for stock-based compensation expense; estimated future cash flows used in calculating the impairment of right-of-use lease assets; and estimated cost to complete performance obligations related to revenue recognition. Recently Adopted Accounting Pronouncement We early adopted the Financial Accounting Standards Board’s Accounting Standards Update 2020-06, “Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity” (“ASU 2020-06”), effective as of January 1, 2023 using the modified retrospective method. Among other amendments, ASU 2020-06 eliminates the cash conversion and beneficial conversion feature models in ASC 470-20 that require an issuer of certain convertible debt and preferred stock to separately account for embedded conversion features as a component of equity, as well as changed the accounting for diluted earnings‑per‑share for convertible instruments and contracts that may be settled in cash or stock. Additionally, ASU 2020-06 requires that the if‑converted method, which is more dilutive than the treasury stock method, be used for all convertible instruments. We applied ASU 2020-06 to all Series A Preferred Stock during 2023, accordingly the Company did not apply the cash conversion or beneficial conversion feature models in its analysis of the Series A Preferred Stock.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. 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, 2023 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 18,861 $ — $ — $ 18,861 Total financial assets $ 18,861 $ — $ — $ 18,861 Liabilities: Forward contract liability $ — $ 164,382 $ — $ 164,382 Parapyre Option Obligation — 279 — 279 CVR liability — — 29,500 29,500 Total liabilities $ — $ 164,661 $ 29,500 $ 194,161 December 31, 2022 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 15,250 $ — $ — $ 15,250 Commercial paper — 23,641 — 23,641 U.S. government securities — 4,230 — 4,230 Corporate bonds — 3,732 — 3,732 Total financial assets $ 15,250 $ 31,603 $ — $ 46,853 The Company measures the fair value of money market funds on quoted prices in active markets for identical assets or liabilities. The Level 2 assets include commercial paper, U.S. government securities 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. The forward contract liability and the Parapyre Option Obligation are considered Level 2 liabilities based on observable market data for substantially the full term of the liabilities. The forward contract liability was initially measured at its estimated fair value on the transaction date based on the underlying price per share on an as-converted basis of the Series A Preferred Stock issued in the PIPE. Subsequent remeasurement of the fair value of the forward contract liability as of June 30, 2023, was based on the market price of the Company's common stock, which represents the redemption value of the Series A Preferred Stock, with the change in value recorded as Change in fair value of forward contract liability within Other Income (Expense). 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 pro-rated 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 testing services within Research and development expenses. The CVR liability value is based on significant inputs not observable in the market such as estimated cash flows, estimated probabilities of success, and risk-adjusted discount rates, which represent a Level 3 liability. As of December 31, 2022, the Company had no financial liabilities outstanding measured at fair value. 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 (see Note 7). 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. Parapyre Option Obligation On June 22, 2023, in connection with the Asset Acquisition, the Company assumed the Parapyre Option Obligation which provided for an annual equity grant of options for Parapyre to purchase 1 % of the then outstanding shares of Spyre's common stock, on a fully diluted basis, on the last business day of each calendar year during the term of the Paragon Agreement, at the fair market value determined by the board of directors of Spyre. As a result of the Asset Acquisition the Parapyre Option Obligation shall continue and Parapyre shall be entitled to receive the equivalent shares of the Company with the same terms. As of June 30, 2023, the pro-rated estimated fair value of the options to be granted on December 31, 2023, was approximately $ 0.3 million, of which $ 0.1 million was recognized as part of the liabilities assumed with the Asset Acquisition on June 22, 2023. 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. CVR Liability In connection with the Asset Acquisition, a non-transferable contingent value right (a “CVR”) was distributed to Aeglea stockholders of record as of the close of business on July 3, 2023, but was not distributed to holders of shares of Common Stock or Series A Preferred Stock issued to the Investors or former stockholders of Spyre in connection with the Transactions. Holders of the CVR will be entitled to receive certain cash payments from proceeds received by us, if any, related to the disposition or monetization of Aeglea’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 condensed 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 success, and risk-adjusted 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, 2023 Estimated cash flow dates 11/28/23 - 06/22/26 Estimated probability of success 27 % - 100 % Risk-adjusted discount rates 7.37 % - 7.94 % The change in fair value between June 22, 2023 and June 30, 2023 was immaterial as none of the significant inputs changed during that time as there were no regulatory updates that would have impacted the probability weights or timing of expected cash flows. The following table presents changes in the CVR liability for the periods presented (in thousands): June 30, 2023 Beginning balance as of December 31, 2022 $ — Fair value at CVR issuance 29,500 Ending Balance as of June 30, 2023 $ 29,500

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	6 Months Ended
	Jun. 30, 2023
Investments Debt And Equity Securities [Abstract]
Cash Equivalents and Marketable Securities	4. 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, 2023 Amortized Gross Gross Estimated Cash equivalents: Money market funds $ 18,861 $ — $ — $ 18,861 Total cash equivalents $ 18,861 $ — $ — $ 18,861 December 31, 2022 Amortized Gross Gross Estimated Cash equivalents: Money market funds $ 15,250 $ — $ — $ 15,250 Commercial paper 7,021 1 ( 2 ) 7,020 U.S. government securities 3,736 — ( 1 ) 3,735 Total cash equivalents $ 26,007 $ 1 $ ( 3 ) $ 26,005 Marketable securities: Commercial paper $ 16,644 $ 2 $ ( 25 ) $ 16,621 Corporate bonds 3,738 — ( 6 ) 3,732 U.S. government securities 495 — — 495 Total marketable securities $ 20,877 $ 2 $ ( 31 ) $ 20,848 As of June 30, 2023, the Company did not hold any available-for-sale securities. 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 December 31, 2022, aggregated by major security type and length of time in a continuous unrealized loss position: December 31, 2022 Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized Commercial paper $ 17,699 $ ( 27 ) $ — $ — $ 17,699 $ ( 27 ) U.S. government securities 3,735 ( 1 ) — — 3,735 $ ( 1 ) Corporate bonds 3,732 ( 6 ) — — 3,732 ( 6 ) Total marketable securities $ 25,166 $ ( 34 ) $ — $ — $ 25,166 $ ( 34 ) 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, 2023 and December 31, 2022, an allowance for credit losses had no t 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 no t consider these marketable securities to be impaired as of June 30, 2023 and December 31, 2022. The financial instruments that potentially subject the Company to a concentration of credit risk consist principally of cash deposits. Accounts at each of our three U.S. banking institutions are insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $ 250,000 per depositor. At June 30, 2023 and December 31, 2022, the Company ha d $ 215.6 million and $ 23.5 million, respectively, of U.S. cash deposits in excess of the FDIC insured limit. Uninsured foreign cash deposits were immaterial for both periods. There we re no realized gains or losses on marke table securities for the three and six months ended June 30, 2023 and 2022. Interest on marketable securities is included in interest income. Accrued interest receivable on available-for-sale debt securities was $ 0.1 million at each of June 30, 2023 and December 31, 2022, and is excluded from the estimate of credit losses. The following table summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands): June 30, December 31, 2023 2022 Due in one year or less $ — $ 20,848 Due thereafter — — Total marketable securities $ — $ 20,848 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, 2023
Accrued Liabilities And Other Liabilities [Abstract]
Accrued and Other Current Liabilities	5. Accrued and Other Current Liabilities Accrued and other current liabilities consist of the following (in thousands): June 30, December 31, 2023 2022 Accrued financing fees for the PIPE $ 12,677 $ — Accrued compensation 7,240 4,589 Accrued contracted research and development costs 4,450 6,972 Accrued professional and consulting fees 3,674 946 Accrued other 386 330 Total accrued and other current liabilities $ 28,427 $ 12,837

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2023
Related Party Transactions [Abstract]
Related Party Transactions	6. Related Party Transactions Paragon and Parapyre, a related party of Paragon, together beneficially own more than 5 % of our capital stock through their holdings of our common stock and Series A Preferred Stock. Fairmount Funds Management LLC ("Fairmount") beneficially owns more than 5 % of our capital stock, has two seats on our Board and beneficially owns more than 5 % of Paragon, which is a joint venture between Fairmount and Fair Journey Biologics. Fairmount has 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 connection with the Asset Acquisition, we assumed the rights and obligations of Spyre under the Paragon Agreement. Under the Paragon Agreement, we are obligated to compensate Paragon on a quarterly basis for its services performed under each research program based on the actual costs incurred. As of the date of the Asset Acquisition, Spyre had incurred total expenses of $ 19.3 million under the Paragon Agreement since inception, inclusive of a $ 3.0 million research initiation fee that was due upon signing of the Paragon Agreement and $ 16.3 million of reimbursable expenses under the Paragon Agreement for historical costs incurred by Paragon. As of the acquisition date, $ 19.3 million was unpaid and was assumed by us through the Asset Acquisition. In July 2023, we exercised our option for the SPY001 program with the remaining three options for the SPY002, SPY003, SPY004 programs remaining outstanding. Following the execution of the SPY001 License Agreement, we are obligated to pay Paragon up to $ 22.0 million upon the achievement of specific development and clinical milestones for the first product under the SPY001 License Agreement that achieves such specified milestones. The following is the summary of expenses related to Paragon and ultimately settled in cash (in millions): Three Months Ended Six Months Ended June 30, June 30, 2023 2022 2023 2022 Financial Statement Line Item Reimbursable costs under the Paragon Agreement $ 1.2 $ — $ 1.2 $ — Research and development For the three and six months ended June 30, 2022 and 2023, no cash payments were made to Paragon. Parapyre Option Obligation The Paragon Agreement provided for an annual equity grant of options to purchase 1 % of the then outstanding shares of Spyre’s common stock, on a fully diluted basis, on the last business day of each calendar year, at the fair market value determined by the board of directors of Spyre (the “Parapyre Option Obligation”). In connection with the Asset Acquisition, we assumed the rights and obligations of Spyre under the Paragon Agreement, including the Parapyre Option Obligation. As a result, the Parapyre Option Obligation shall continue and Parapyre shall be entitled to receive the equivalent shares of the Company with the same terms. See Note 10 for disclosures 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. The following is the summary of Related party accounts payable (in millions): June 30, December 31, 2023 2022 Reimbursable costs under the Paragon Agreement $ 20.5 $ — Parapyre Option Obligation liability 0.3 — Total related party accounts payable $ 20.8 $ —

Asset Acquisition

Asset Acquisition	6 Months Ended
	Jun. 30, 2023
Asset Acquisition [Abstract]
Asset Acquisition	7. Asset Acquisition On June 22, 2023, we acquired 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 Spyre. Pursuant to the Acquisition Agreement, First Merger Sub merged with and into Spyre, pursuant to which Spyre was the surviving corporation and became a wholly owned subsidiary of the Company (the “First Merger”). Immediately following the First Merger, Spyre merged with and into Second Merger Sub, pursuant to which Second Merger Sub became the surviving entity. 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 Spyre, in accordance with the terms of the Acquisition Agreement. Under the terms of the Acquisition Agreement, the Company issued 12,945,385 shares of common stock and 364,887 shares of Series A Preferred Stock to former Spyre security holders. In addition, outstanding and unexercised stock options to purchase 68,365 shares of common stock were assumed from the Amended and Restated Spyre 2023 Equity Incentive Plan. The issuance of these shares of common stock and Series A Preferred Stock occurred on July 7, 2023. Accordingly, as of June 30, 2023, 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 Company's 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. The Company concluded that the arrangement meets the definition of an asset acquisition rather than a business combination, as substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset, Spyre's option (the "Option") to exclusively license IPR&D. We determined that the Option to license IPR&D was a single asset as the Company's strategy relies on developing the entire portfolio of individual treatments to create combination treatments that simultaneously address different mechanisms of irritable bowel disease with a single treatment. The Company also determined that the pipeline candidates within the portfolio are 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 IPR&D. The fair value of the consideration issued consisted of the 364,887 shares of Series A Preferred Stock ( 364,887,000 shares of common stock on an as-converted basis) and 12,945,385 shares of common stock, valued at $ 291.08 per share and $ 0.29108 per share, respectively. The Asset Acquisition cost are shown on the following table (in millions): June 22, 2023 Consideration transferred in Series A Preferred Stock and common stock $ 110.0 Transaction costs incurred by Aeglea 3.2 Fair value of Parapyre Option Obligation assumed by Aeglea 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, 2023 Acquired in-process research and development $ 130.5 Cash acquired 3.0 Assumed liabilities ( 20.2 ) Total cost to acquire asset $ 113.3

Paragon Agreement

Paragon Agreement	6 Months Ended
	Jun. 30, 2023
Collaborative Arrangement [Abstract]
Paragon Agreement	8. Paragon Agreement In May 2023, Spyre entered into the Paragon Agreement with Paragon and Parapyre. In consideration for the Option granted under the Paragon Agreement, Spyre was obligated to pay Paragon an upfront cash amount of $ 3.0 million in research initiation fees. In addition, Spyre was obligated to pay incurred reimbursable research costs of $ 16.3 million to Paragon as of the closing of the Asset Acquisition. Furthermore, the Paragon Agreement provided for an annual equity grant of options to purchase 1 % of the then outstanding shares of Spyre’s common stock, on a fully diluted basis, on the last business day of each calendar year, during the term of the Paragon Agreement, at the fair market value determined by the board of directors of Spyre. As a result of the Asset Acquisition, we assumed the rights and obligations of Spyre under the Paragon Agreement, including the Parapyre Option Obligation. Pursuant to the Paragon Agreement, on a research program-by-research program basis following the finalization of the research plan for each respective research program, we are required to pay Paragon a nonrefundable fee in cash of $ 0.8 million. We are also obligated to compensate Paragon on a quarterly basis for its services performed under each research program based on the actual costs incurred. For the period from June 22, 2023 (Asset Acquisition date) to June 30, 2023, we incurred $ 1.2 million of costs reimbursable to Paragon under the Paragon Agreement. For the three and six months ended June 30, 2023 and 2022, we did no t make any payments to Paragon. On July 12, 2023, we exercised our Option available under the Paragon Agreement with respect to the SPY001 research program and will enter into a SPY001 license agreement (the “SPY001 License Agreement”). Our Option available under the Paragon Agreement with respect to the SPY002, SPY003 and SPY004 programs remains unexercised. Following the execution of the SPY001 License Agreement, we are also obligated to pay Paragon up to $ 22.0 million upon the achievement of specific development and clinical milestones for the first product under the SPY001 License Agreement that achieves such specified milestones. Upon execution of the SPY001 License Agreement, we will pay Paragon a $ 1.5 million fee for nomination of a development candidate, and we are obligated to make a further milestone payment of $ 2.5 million upon the first dosing of a human patient in a Phase 1 trial. Subject to the execution of the Option with respect to the SPY002, SPY003 or SPY004 research programs, we expect to be obligated to make similar payments upon and following the execution of license agreements with respect to the these research programs, respectively. Prior to the Asset Acquisition, Spyre had incurred total expenses of $ 19.3 million under the Paragon Agreement, inclusive of a $ 3.0 million research initiation fee that was due upon signing of the Paragon Agreement and $ 16.3 million of reimbursable expenses under the Paragon Agreement for historical costs incurred by Paragon . As of the acquisition date, $ 19.3 million was unpaid and was assumed by us through the Asset Acquisition.

Series A Non-Voting Convertible

Series A Non-Voting Convertible Preferred Stock	6 Months Ended
	Jun. 30, 2023
Equity [Abstract]
Series A Non-Voting Convertible Preferred Stock	9. 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 “Certificate of Designation”) in connection with the Asset Acquisition and the PIPE. The Certificate of Designation authorizes the issuance of 1,086,341 shares of Series A Preferred Stock, par value $ 0.0001 per share. 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 our Common Stock. Except as provided in the 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, we 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 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 “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 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. The Company has agreed to hold a stockholders’ meeting to submit the following matters to its stockholders for their consideration: (i) the approval of the Conversion Proposal , and (ii) if deemed necessary or appropriate by the Company or as otherwise required by law or contract, the approval of an amendment to the Certificate of Incorporation to authorize sufficient shares of common stock for the conversion of the Series A Preferred Stock issued pursuant to the Acquisition Agreement and/or to effectuate a reverse stock split of all outstanding shares of common stock at a reverse stock split ratio to be reasonably determined by the Company for the purpose of maintaining compliance with Nasdaq listing standards. In connection with these matters, the Company filed with the SEC a preliminary proxy statement and other relevant materials. The stockholder meeting and reverse stock split have not occurred as of June 30, 2023. The Series A Preferred Stock is recorded outside of stockholders’ (deficit) equity because, if conversion to common stock is not approved by the stockholders, the Series A Preferred Stock will be redeemable at the option of the holders for cash equal to the closing price of the common stock per share of common stock underlying the Series A Preferred Stock, on the last trading day prior to the holder’s redemption request. As of June 30, 2023, the redemption value of the Company's outstanding Series A Preferred Stock was $ 325.0 million based on the closing stock price of the Company's common stock on June 30, 2023 of $ 0.4505 per share. The Company determined that the conversion and redemption features of the Series A Preferred Stock do not require bifurcation as derivatives. Following stockholder approval of the Conversion Proposal, each share of Series A Preferred Stock will automatically convert into 1,000 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 % and 19.99 %) of the total number of shares of common stock issued and outstanding immediately after giving effect to such conversion. 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 $ 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. On August 8, 2023, the Company filed a preliminary proxy statement with the SEC to solicit approval of the Conversion Proposal, among other matters, at a special meeting of stockholders.

Liabilities, Convertible Prefer

Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity	6 Months Ended
	Jun. 30, 2023
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity	10. Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity Registered Direct Offering In May 2022, the Company issued and sold 10,752,688 shares of common stock at an offering price of $ 1.60 per share and pre-funded warrants to purchase up to 17,372,312 shares of common stock at an offering price of $ 1.5999 per warrant (representing the price per share of common stock sold in the offering minus the $ 0.0001 exercise price per warrant) in a registered direct offering pursuant to a shelf registration statement on Form S-3. The net proceeds to the Company from this offering were approximately $ 42.9 million, after deducting placement agent fees and offering costs of $ 2.1 million. 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 $ 0.0001 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, 2023, the following pre-funded warrants for common stock were issued and outstanding: Issue Date Expiration Date Exercise Price Number of Warrants Outstanding February 8, 2019 None $ 0.0001 — April 30, 2020 None $ 0.0001 — May 20, 2022 None $ 0.0001 13,281,250 Total pre-funded warrants 13,281,250 As of August 4, 2023, an additional 7,031,250 pre-funded warrants have been exercised. Stock-Based Compensation 2016 Equity Incentive Plan The 2016 Equity Incentive Plan (“2016 Plan”) 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 (through 2028) equal to (a) 4.0 % of the number of issued and outstanding shares of common stock on December 31 of the immediately preceding year, or (b) a lesser amount as approved by the Company’s board of directors each year. As a result of this provision, on January 1, 2023 and January 1, 2022, an additional 2,614,013 and 1,974,205 shares, respectively, became available for issuance under the 2016 Plan. In July 2020, the Company granted 228,200 restricted stock units ("RSUs"), to certain employees, with vesting terms subject to regulatory, commercial, and clinical milestones, in addition to a service condition. As of June 30, 2023, none of these RSUs had vested and all RSUs were forfeited since the performance milestones were not met within the required time frame. No stock-based compensation expense was recognized on these awards. On June 22, 2023, concurrent with the closing of the Asset Acquisition, the Company’s board of directors approved an amendment of the 2016 Plan to eliminate the per-participant annual award limits originally intended to comply with the qualified performance-based compensation exception set forth in Section 162(m) of the Internal Revenue Code, in light of the repeal of such exception pursuant to the Tax Cuts and Jobs Act of 2017. In addition, the Company approved 68,000,955 options contingent on stockholder approval to certain members of the board of directors, legacy Aeglea employees and consultants under the 2016 Plan. These awards are in excess of the shares available for issuance under the 2016 Plan and require stockholder approval before being granted. Accordingly, no expense has been recognized on these contingent awards since they are contingent on stockholder approval. As of June 30, 2023 , the 2016 Plan had 5,384,315 shares available for future issuance. 2018 Equity Inducement Plan On June 22, 2023, the Company's board of directors approved an increase of 70,000,000 in the number of shares reserved for issuance to the 2018 Equity Inducement Plan and granted 63,417,415 inducement awards to new hires. The grant-date fair value of these inducement awards will be recognized as expense on a pro-rata basis over the vesting period. The awards have an exercise price of $ 0.30 per option, vest ratably over four years , and have a ten-year exercise period from the grant date. 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 (the "Spyre Equity Plan") and its outstanding and unexercised stock options which were converted to options to purchase 68,365 shares of Aeglea 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. Parapyre Option Obligation On June 22, 2023, in connection with the Asset Acquisition, the Company assumed the Parapyre Option Obligation which provided for an annual equity grant of options to purchase 1 % of the then outstanding shares of Spyre's common stock, on a fully diluted basis, on the last business day of each calendar year during the term of the Paragon Agreement, at the fair market value determined by the board of directors of Spyre. As a result of the Asset Acquisition the Parapyre Option Obligation shall continue and Parapyre shall be entitled to receive the equivalent shares of the Company with the same terms. As of June 30, 2023, the pro-rated estimated fair value of the options to be granted on December 31, 2023, was approximately $ 0.3 million, of which $ 0.1 million was recognized as part of the liabilities assumed with the Asset Acquisition. 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, 2023, the unamortized expense related to the Parapyre Option Obligation was $ 1.3 million. The following table summarizes the Company’s stock awards granted under all plans for each of the periods indicated: Three Months Ended June 30, 2023 2022 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 63,417,415 $ 0.30 429,000 $ 0.96 2016 Employee Stock Purchase Plan Under the Company’s 2016 Employee Stock Purchase Plan (“2016 ESPP”), the Company issued and sold 44,816 shares for aggregate cash proceeds of less than $ 0.1 million during the six months ended June 30, 2023. There were 64,743 shares issued and sold under the 2016 ESPP for aggregate cash proceeds of $ 0.2 million during the six months ended June 30, 2022. Stock-based Compensation Expense Total stock-based compensation expense related to all plans was as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2023 2022 2023 2022 Research and development $ 394 $ 691 $ 1,171 $ 1,392 General and administrative 1,517 1,327 2,449 2,726 Total stock-based compensation expense $ 1,911 $ 2,018 $ 3,620 $ 4,118 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 2016 Plan, and the shares purchasable under the 2016 ESPP during the periods presented: Three Months Ended Six Months Ended June 30, June 30, 2023 2022 2023 2022 2016 Plan Expected term (in years) 6.03 5.98 6.03 6.01 Expected volatility 117 % 82 % 115 % 82 % Risk-free interest 3.98 % 2.96 % 3.99 % 2.07 % Dividend yield — — — — 2016 ESPP Expected term (in years) — — 0.49 0.49 Expected volatility — — 181 % 76 % Risk-free interest — — 4.99 % 1.09 % Dividend yield — — — —

Strategic License Agreements

Strategic License Agreements	6 Months Ended
	Jun. 30, 2023
License And Collaboration Agreement [Abstract]
Strategic License Agreements	11. Strategic License Agreements On March 21, 2021 , the Company entered into an exclusive license and supply agreement with Immedica Pharma AB (“Immedica”) (the "Immedica Agreement"). By entering into this agreement, the Company agreed to provide Immedica the following goods and services: i. Deliver an exclusive, sublicensable, license and know-how (the “License”) to develop and commercialize pegzilarginase (the “Product”) in the territory comprising the members states of the European Economic Area ("EEA"), United Kingdom ("UK"), Switzerland, Andorra, Monaco, San Marino, Vatican City, Turkey, Saudi Arabia, United Arab Emirates, Qatar, Kuwait, Bahrain, and Oman (the “Territory”); ii. Complete the global pivotal PEACE (Pegzilarginase Effect on Arginase 1 Deficiency Clinical Endpoints) Phase 3 trial (“PEACE Trial”) and related Biologics License Application (“BLA”) package to file with the United States Food and Drug Administration (“FDA”), which will be leveraged by Immedica in obtaining the necessary regulatory approvals in the Territory; and iii. Perform a Pediatric Investigation Plan trial (“PIP Trial”) in order for Immedica to be able to receive certain regulatory approvals within the Territory. In addition, the Company and Immedica formed a Joint Steering Committee (“JSC”) to provide oversight to the activities performed under the agreement; however, the substance of the Company’s participation in the JSC does not represent an additional promised service, but rather, a right of the Company to protect its own interests in the arrangement. Further, the Company agreed to supply to Immedica, and Immedica agreed to purchase from the Company, substantially all commercial requirements of the Product. The terms of the agreement do not provide for either (i) an option to Immedica to purchase the Product from the Company at a discount from the standalone selling price or (ii) minimum purchase quantities. Finally, Immedica will bear (i) all costs and expenses for any development or commercialization of the Product in the Territory subject to the License exclusive of the Company’s promised goods and services summarized above and (ii) all costs and fees associated with applying for regulatory approval of the Product in the Territory. The Company received a non-refundable payment of $ 21.5 million and Immedica agreed to provide payment of 50 % of the Company’s costs incurred in performing the PIP Trial up to a maximum of $ 1.8 million. In addition, the Company had the ability to receive regulatory and commercial milestone payments. Th e Company was also entitled to receive royalties in the mid-20% range on net sales of the Product in the Territory. In July 2021, the Company modified the agreement with Immedica to provide certain additional services in relation to the PEACE Trial and BLA package performance obligation in exchange for the reimbursement of up to $ 3.0 million of the actual costs incurred in relation to such incremental services. The Company concluded that Immedica meets the definition to be accounted for as a customer because the Company is delivering intellectual property and other services within the Company’s normal course of business, in which the parties are not jointly sharing the risks and rewards. Therefore, the Company concluded that the promises summarized above represent transactions with a customer within the scope of ASC 606. The Company determined that the following promises represent distinct promised services, and therefore, performance obligations: (i) the License, (ii) the PEACE Trial and BLA package, and (iii) the PIP Trial. Specifically, in making these determinations, the Company considered the following factors: - As of inception of the agreement, the Company had completed the Phase 1/2 clinical trial related to the Product and were conducting the PEACE Trial. Accordingly, the Company is not promising, nor expecting, to perform additional research and development activities pursuant to the agreement that would either significantly modify, customize or be considered highly interdependent or interrelated with pegzilarginase. - The License represents functional intellectual property given the functionality of the License is not expected to change substantially as a result of the company’s ongoing activities. - The services necessary to complete the PEACE Trial, BLA package and PIP Trial could be performed by other parties. Given that Immedica is not obligated to purchase any minimum amount or quantities of Product, the supply of Product for commercial use to Immedica was determined to be an option for Immedica, rather than a performance obligation of the Company at contract inception and will be accounted for if and when exercised. The Company also determined that Immedica’s option to purchase the Product does not create a material right as the expected pricing is not at a discount. The Company determined that the upfront fixed payment amount of $ 21.5 million must be included in the transaction price. Additionally, the Company determined at inception of the arrangement that 50 % of the probable estimated costs to be incurred in relation to the PIP Trial exceeded $ 1.8 million and included the full reimbursement amount of $1.8 million in the transaction price. Upon subsequent re-evaluation due to changing facts and circumstances, the Company determined the probable estimated costs are now less than the maximum allowable reimbursement and a portion of the variable consideration was constrained, which did not materially impact the revenue recognized to date. Additionally, upon the modification of the agreement in July 2021, the Company determined that the probable estimated costs to perform the additional services related to the PEACE Trial and BLA package exceeds the maximum allowable reimbursement of $ 3.0 million. Therefore, the Company included an estimated total of $ 3.6 million that was due in relation to the PIP Trial, PEACE Trial, and BLA package in the transaction price and it is probable that a significant reversal will not occur in the future. In total, the modified transaction price was determined to be $ 25.1 million. The Company has allocated $ 9.6 million and $ 3.5 million of the modified transaction price to the PEACE Trial and BLA package and PIP Trial performance obligations, respectively, based on the stand-alone selling prices ("SSP"), which were based on the estimated costs that a third-party would charge in performing such services on a stand-alone basis. The SSP for the License was established at inception of the arrangement using a residual value approach due to the uniqueness of and lack of observable data related to the License, and without a specific analog from which to make reliable estimates, resulting in an allocation of $ 12.0 million. The potential regulatory milestone payments that the Company is eligible to receive were excluded from the transaction price, as the milestone amounts were fully constrained based on the probability of achievement, since the milestones relate to successful achievement of certain regulatory approvals, which might not be achieved. The Company determined that the royalties and commercial milestone payments relate predominantly to the license of intellectual property and are therefore excluded from the transaction price under the sales- or usage-based royalty exception of Topic 606. The Company will reevaluate the transaction price, including all constrained amounts, at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, the Company will adjust its estimate of the transaction price as necessary. The Company will recognize the royalties and commercial milestone payments as revenue when the associated sales occur, and relevant sales-based thresholds are met. The Company assessed the arrangement with Immedica and concluded that a significant financing component does not exist. The Company recognized revenue allocated to the License performance obligation at a point in time and upon transfer of the License. The Company completed the transfer of the know-how necessary for Immedica to benefit from the License in June 2021 and recognized $ 12.0 million of revenue at that time. The development fee allocated to the PEACE Trial, BLA package and PIP Trial performance obligations is recognized over time using an input method of costs incurred related to the performance obligations. For the three and six months ended June 30, 2023, the Company recognized $ 0.7 , and $ 0.9 million, respectively, under the Immedica Agreement. The total revenue generated in the three months ended June 30, 2023, was attributable to drug supply and royalties from an early access program in France. The total revenue generated in the six months ended June 30, 2023, was attributable to the PEACE Phase 3 and PIP trials, drug supply, and royalties from an early access program in France. For the three and six months ended June 30, 2022, the Company recognized revenue of $ 0.6 million, and $ 2.0 million, respectively related to the PEACE Trial and BLA package performance obligation. As of June 30, 2023 , and 2022, the Company has recorded deferred revenue of $ 3.3 million and $ 2.7 million, respectively, associated with the Immedic a agreement, of which $ 0.9 million and $ 0.3 million was classified as current, respectively. On July 27, 2023, the Company announced that it had entered into an agreement to sell the global rights to pegzilarginase to Immedica and concurrently terminated the existing Immedica Agreement. Any remaining deferred revenue is expected to be recognized as part of the gain on disposal of the assets. Contract Balances from Customer Contract The timing of revenue recognition, billings and cash collections results in contract assets and contract liabilities on the 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 following table presents changes in the Company’s contract liabilities for the periods presented (in thousands): December 31, June 30, Six Months Ended June 30, 2023 2022 Additions Deductions 2023 Contract liabilities: Deferred revenue $ 2,696 $ 628 $ ( 53 ) $ 3,271 The Company had no contract assets during the six months ended June 30, 2023 and 2022 .

Restructuring Charges

Restructuring Charges	6 Months Ended
	Jun. 30, 2023
Restructuring and Related Activities [Abstract]
Restructuring Charges	13. Restructuring Charges Severance and Stock Compensation On April 12, 2023, based on the review of the inconclusive interim results from our 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 one-time cash severance payments and other employee-related costs of $ 6.4 million during the three and six months ended June 30, 2023. Cash payments for employee related restructuring charges of $ 2.2 million were paid as of June 30, 2023. 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. The following table summarizes the changes in the Company's accrued restructuring balance (in thousands): Beginning Balance Ending Balance December 31, 2022 Charges Payments June 30, 2023 Severance liability $ — $ 6,448 $ ( 2,200 ) $ 4,248 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 losses of $ 0.9 million related to the operating lease right-of-use asset and $ 1.7 million related to leasehold improvements. As of June 30, 2023, the Company was in default of its lease obligations by abandoning the leased space. As a result, the full remaining lease liability is classified as a current liability as the lessor can call all future required payments to be made immediately. A summary of the charges related to the restructuring activities as of June 30, 2023 is as follows (in thousands): Severance and related Stock compensation 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

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Jun. 30, 2023
Earnings Per Share [Abstract]
Net Loss Per Share	12. 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 do not have an obligation to fund losses and therefore the Series A Preferred Stock was excluded from the calculation of basic net loss per share. The Company included in the calculation of basic net loss per share, contingently issuable common shares related to the Asset Acquisition because they will be issued for no consideration due to the consideration already having been satisfied as of June 30, 2023. 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 June 30, June 30, 2023 2022 2023 2022 Options to purchase common stock 16,363,183 8,566,549 13,937,881 8,113,849 Unvested restricted stock units — 181,500 9,519 186,243 Series A Preferred Stock (on an as-converted basis) 39,640,000 — 19,930,000 —

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2023
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events On July 7, 2023, the Company settled its forward contract liability by issuing the underlying Series A Preferred Stock to the former Spyre shareholders. On July 27, 2023, the Company announced that it has 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 supersedes and terminates the previous license agreement between the Company and Immedica. 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. The upfront payment and contingent milestone payments if paid, net of expenses and adjustments, will be distributed to holders of Aeglea’s CVR pursuant to the CVR Agreement resulting from the Asset Acquisition. On August 7, 2023, the Company terminated its building lease in Austin, Texas. The negotiated termination agreement obligates 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.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2023
Accounting Policies [Abstract]
Convertible Preferred Stock Issued through PIPE	Convertible Preferred Stock Issued through PIPE The Company records shares of convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The Company has applied the guidance in ASC 480-10-S99-3A, SEC Staff Announcement: Classification and Measurement of Redeemable Securities, and has therefore classified the Series A Preferred Stock outside of stockholders’ (deficit) equity because, if conversion to common stock is not approved by the stockholders, the Series A Preferred Stock will be redeemable at the option of the holders for cash equal to the closing price of the common stock on the last trading day prior to the holder’s redemption request. The Company determined that the conversion and redemption are outside of the Company’s control. Additionally, the Company determined the conversion and redemption features did not require bifurcation as derivatives.
Acquisitions	Acquisitions The Company evaluates acquisitions of assets and other similar transactions to assess whether or not the transaction should be accounted for as a business combination or asset acquisition by first applying a screen test to determine whether substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. If so, the transaction is accounted for as an asset acquisition. If not, further determination is required as to whether or not the Company has acquired inputs and processes that have the ability to create outputs, which would meet the definition of a business. Significant judgment is required in the application of the screen test to determine whether an acquisition is a business combination or an acquisition of assets. Acquisitions meeting the definition of business combinations are accounted for using the acquisition method of accounting, which requires that the purchase price be allocated to the net assets acquired at their respective fair values. In a business combination, any excess of the purchase price over the estimated fair values of the net assets acquired is recorded as goodwill. The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the assets, which includes transaction costs. Goodwill is not recognized in asset acquisitions. When a transaction accounted for as an asset acquisition includes an in-process research and development (“IPR&D”) asset, the IPR&D asset is only capitalized if it has an alternative future use other than in a particular research and development project. Otherwise, the cost allocated to acquire an IPR&D with no alternative future use is charged to expense at the acquisition date.
Contingent Value Rights	Contingent Value Rights The Company evaluates its contracts to determine if those contracts qualify as derivatives under ASC 815, Derivatives and Hedging . For derivative financial instruments that are accounted for as liabilities, the derivative instrument is initially recorded at its fair value and is then re-valued at each reporting date. Any changes in fair value are recorded as other income or expense for each reporting period. Derivative instrument liabilities are classified in the balance sheet as current or non-current based on whether or not net-cash settlement of the derivative instrument is probable within the next 12 months from the balance sheet date. The Company determined that certain contingent payments under the CVR Agreement qualified as derivatives under ASC 815, and as such, were recorded as a liability on the balance sheet as of June 30, 2023. The Company applies a scenario-based method and weights them based on the possible achievement of certain milestones. 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. This fair value measurement is based on significant inputs not observable in the market and thus represents a Level 3 measurement as defined in ASC 820, Fair Value Measurement . The key assumptions used include the discount rate, probability of regulatory success, and reimbursement rates from certain government agencies. The estimated value of the CVR consideration is based upon available information and certain assumptions which the Company's management believes are reasonable under the circumstances. The ultimate payout under the CVRs may differ materially from the assumptions used in determining the fair value of the CVR consideration. This value is then remeasured for future expected payout as well as the increase in fair value due to the time value of money. These gains or losses, if any, are recognized in the consolidated statements of operations and comprehensive loss.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets, liabilities, and equity and the amount of revenues and expenses. Actual results could differ significantly from those estimates. The most significant estimates and assumptions that management considers in the preparation of the Company's financial statements relate to accrued research and development costs; the valuation of consideration transferred in acquiring IPR&D; the discount rate, probabilities of success, and timing of estimated cash flows in the valuation of the CVR liability; inputs used in the Black-Scholes model for stock-based compensation expense; estimated future cash flows used in calculating the impairment of right-of-use lease assets; and estimated cost to complete performance obligations related to revenue recognition.
Recently Adopted Accounting Pronouncement	Recently Adopted Accounting Pronouncement We early adopted the Financial Accounting Standards Board’s Accounting Standards Update 2020-06, “Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity” (“ASU 2020-06”), effective as of January 1, 2023 using the modified retrospective method. Among other amendments, ASU 2020-06 eliminates the cash conversion and beneficial conversion feature models in ASC 470-20 that require an issuer of certain convertible debt and preferred stock to separately account for embedded conversion features as a component of equity, as well as changed the accounting for diluted earnings‑per‑share for convertible instruments and contracts that may be settled in cash or stock. Additionally, ASU 2020-06 requires that the if‑converted method, which is more dilutive than the treasury stock method, be used for all convertible instruments. We applied ASU 2020-06 to all Series A Preferred Stock during 2023, accordingly the Company did not apply the cash conversion or beneficial conversion feature models in its analysis of the Series A Preferred Stock.

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	6 Months Ended
	Jun. 30, 2023
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, 2023 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 18,861 $ — $ — $ 18,861 Total financial assets $ 18,861 $ — $ — $ 18,861 Liabilities: Forward contract liability $ — $ 164,382 $ — $ 164,382 Parapyre Option Obligation — 279 — 279 CVR liability — — 29,500 29,500 Total liabilities $ — $ 164,661 $ 29,500 $ 194,161 December 31, 2022 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 15,250 $ — $ — $ 15,250 Commercial paper — 23,641 — 23,641 U.S. government securities — 4,230 — 4,230 Corporate bonds — 3,732 — 3,732 Total financial assets $ 15,250 $ 31,603 $ — $ 46,853
Schedule of significant inputs used to estimate the fair value of CVR liability	The significant inputs used to estimate the fair value of the CVR liability were as follows: June 30, 2023 Estimated cash flow dates 11/28/23 - 06/22/26 Estimated probability of success 27 % - 100 % Risk-adjusted discount rates 7.37 % - 7.94 %
Schedule of Changes in CVR Liability	The following table presents changes in the CVR liability for the periods presented (in thousands): June 30, 2023 Beginning balance as of December 31, 2022 $ — Fair value at CVR issuance 29,500 Ending Balance as of June 30, 2023 $ 29,500

Cash Equivalents and Marketab_2

Cash Equivalents and Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2023
Investments Debt And Equity Securities [Abstract]
Schedule of Estimated Fair Value of 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, 2023 Amortized Gross Gross Estimated Cash equivalents: Money market funds $ 18,861 $ — $ — $ 18,861 Total cash equivalents $ 18,861 $ — $ — $ 18,861 December 31, 2022 Amortized Gross Gross Estimated Cash equivalents: Money market funds $ 15,250 $ — $ — $ 15,250 Commercial paper 7,021 1 ( 2 ) 7,020 U.S. government securities 3,736 — ( 1 ) 3,735 Total cash equivalents $ 26,007 $ 1 $ ( 3 ) $ 26,005 Marketable securities: Commercial paper $ 16,644 $ 2 $ ( 25 ) $ 16,621 Corporate bonds 3,738 — ( 6 ) 3,732 U.S. government securities 495 — — 495 Total marketable securities $ 20,877 $ 2 $ ( 31 ) $ 20,848
Schedule of Gross Unrealized Losses and Fair Value by Investment Category and Age	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 December 31, 2022, aggregated by major security type and length of time in a continuous unrealized loss position: December 31, 2022 Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized Commercial paper $ 17,699 $ ( 27 ) $ — $ — $ 17,699 $ ( 27 ) U.S. government securities 3,735 ( 1 ) — — 3,735 $ ( 1 ) Corporate bonds 3,732 ( 6 ) — — 3,732 ( 6 ) Total marketable securities $ 25,166 $ ( 34 ) $ — $ — $ 25,166 $ ( 34 )
Summary of 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, 2023 2022 Due in one year or less $ — $ 20,848 Due thereafter — — Total marketable securities $ — $ 20,848

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2023
Accrued Liabilities And Other Liabilities [Abstract]
Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): June 30, December 31, 2023 2022 Accrued financing fees for the PIPE $ 12,677 $ — Accrued compensation 7,240 4,589 Accrued contracted research and development costs 4,450 6,972 Accrued professional and consulting fees 3,674 946 Accrued other 386 330 Total accrued and other current liabilities $ 28,427 $ 12,837

Related Party Transactions (Tab

Related Party Transactions (Tables)	6 Months Ended
	Jun. 30, 2023
Related Party Transactions [Abstract]
Summary of Expenses Related to Paragon and Settled in Cash	The following is the summary of expenses related to Paragon and ultimately settled in cash (in millions): Three Months Ended Six Months Ended June 30, June 30, 2023 2022 2023 2022 Financial Statement Line Item Reimbursable costs under the Paragon Agreement $ 1.2 $ — $ 1.2 $ — Research and development
Summary of Related party Accounts Payable	The following is the summary of Related party accounts payable (in millions): June 30, December 31, 2023 2022 Reimbursable costs under the Paragon Agreement $ 20.5 $ — Parapyre Option Obligation liability 0.3 — Total related party accounts payable $ 20.8 $ —

Asset Acquisition (Tables)

Asset Acquisition (Tables)	6 Months Ended
	Jun. 30, 2023
Asset Acquisition [Line Items]
Schedule of Asset Acquisition Cost	The Asset Acquisition cost are shown on the following table (in millions): June 22, 2023 Consideration transferred in Series A Preferred Stock and common stock $ 110.0 Transaction costs incurred by Aeglea 3.2 Fair value of Parapyre Option Obligation assumed by Aeglea 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, 2023 Acquired in-process research and development $ 130.5 Cash acquired 3.0 Assumed liabilities ( 20.2 ) Total cost to acquire asset $ 113.3

Liabilities, Convertible Pref_2

Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity (Tables)	6 Months Ended
	Jun. 30, 2023
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Pre-funded Warrants for Common Stock Issued and Outstanding	As of June 30, 2023, the following pre-funded warrants for common stock were issued and outstanding: Issue Date Expiration Date Exercise Price Number of Warrants Outstanding February 8, 2019 None $ 0.0001 — April 30, 2020 None $ 0.0001 — May 20, 2022 None $ 0.0001 13,281,250 Total pre-funded warrants 13,281,250
Schedule of Company's Stock Awards Granted	The following table summarizes the Company’s stock awards granted under all plans for each of the periods indicated: Three Months Ended June 30, 2023 2022 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 63,417,415 $ 0.30 429,000 $ 0.96
Summary of Stock-Based Compensation Expense	Total stock-based compensation expense related to all plans was as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2023 2022 2023 2022 Research and development $ 394 $ 691 $ 1,171 $ 1,392 General and administrative 1,517 1,327 2,449 2,726 Total stock-based compensation expense $ 1,911 $ 2,018 $ 3,620 $ 4,118
Schedule of Estimated 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 2016 Plan, and the shares purchasable under the 2016 ESPP during the periods presented: Three Months Ended Six Months Ended June 30, June 30, 2023 2022 2023 2022 2016 Plan Expected term (in years) 6.03 5.98 6.03 6.01 Expected volatility 117 % 82 % 115 % 82 % Risk-free interest 3.98 % 2.96 % 3.99 % 2.07 % Dividend yield — — — — 2016 ESPP Expected term (in years) — — 0.49 0.49 Expected volatility — — 181 % 76 % Risk-free interest — — 4.99 % 1.09 % Dividend yield — — — —

Strategic License Agreements (T

Strategic License Agreements (Tables)	6 Months Ended
	Jun. 30, 2023
License And Collaboration Agreement [Abstract]
Summary of Changes in Contract Liabilities	The following table presents changes in the Company’s contract liabilities for the periods presented (in thousands): December 31, June 30, Six Months Ended June 30, 2023 2022 Additions Deductions 2023 Contract liabilities: Deferred revenue $ 2,696 $ 628 $ ( 53 ) $ 3,271

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2023
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 June 30, June 30, 2023 2022 2023 2022 Options to purchase common stock 16,363,183 8,566,549 13,937,881 8,113,849 Unvested restricted stock units — 181,500 9,519 186,243 Series A Preferred Stock (on an as-converted basis) 39,640,000 — 19,930,000 —

Restructuring Charges (Tables)

Restructuring Charges (Tables)	6 Months Ended
	Jun. 30, 2023
Restructuring and Related Activities [Abstract]
Summary of Accrued Restructuring Balance	The following table summarizes the changes in the Company's accrued restructuring balance (in thousands): Beginning Balance Ending Balance December 31, 2022 Charges Payments June 30, 2023 Severance liability $ — $ 6,448 $ ( 2,200 ) $ 4,248
Summary of Charges Related to the Restructuring Activities	A summary of the charges related to the restructuring activities as of June 30, 2023 is as follows (in thousands): Severance and related Stock compensation 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 - Additional Information (Details) $ / shares in Units, $ in Thousands			1 Months Ended	6 Months Ended
	Jun. 26, 2023 USD ($) shares	Jun. 22, 2023 $ / shares shares	Apr. 30, 2023 Employee	Jun. 30, 2023 USD ($) Segment $ / shares	Dec. 31, 2022 USD ($) $ / shares
Company and Basis of Presentation [Line Items]
Number of operating segments | Segment				1
Preferred stock, par value | $ / shares				$ 0.0001	$ 0.0001
Accumulated deficit | $				$ (661,127)	$ (425,624)
Cash and cash equivalents | $				$ 235,358	$ 34,863
Percentage of existing headcount reduction			83%
Number of employees retained | Employee			10
Asset Acquisition
Company and Basis of Presentation [Line Items]
Fixed exchange ratio		13.73622
Spyre 2023 Equity Incentive Plan | Asset Acquisition
Company and Basis of Presentation [Line Items]
Outstanding and unexercised stock options | shares		68,365
Series A Preferred Stock
Company and Basis of Presentation [Line Items]
Preferred stock, par value | $ / shares		$ 0.0001
Conversion basis		1,000
Series A Preferred Stock | Asset Acquisition
Company and Basis of Presentation [Line Items]
Asset acquisition consideration transferred equity interest issued, shares | shares		364,887
Preferred stock, par value | $ / shares		$ 0.0001
Conversion basis		1,000
Private Placement | Series A Preferred Stock
Company and Basis of Presentation [Line Items]
Number of shares | shares	721,452
Aggregate purchase price of shares | $	$ 210,000
Placement agent and other offering expenses | $	$ 12,700
Common Stock | Asset Acquisition
Company and Basis of Presentation [Line Items]
Asset acquisition consideration transferred equity interest issued, shares | shares		12,945,385

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Jun. 22, 2023	Dec. 31, 2022
Forward Contract Liability
Financial Assets:
Liabilities, fair value	$ 164,400	$ 106,200
Fair Value, Measurements, Recurring
Financial Assets:
Financial assets, fair value	18,861		$ 46,853
Liabilities, fair value	194,161
Fair Value, Measurements, Recurring | Corporate bonds
Financial Assets:
Financial assets, fair value			3,732
Fair Value, Measurements, Recurring | Commercial paper
Financial Assets:
Financial assets, fair value			23,641
Fair Value, Measurements, Recurring | Level 1
Financial Assets:
Financial assets, fair value	18,861		15,250
Fair Value, Measurements, Recurring | Level 2
Financial Assets:
Financial assets, fair value			31,603
Liabilities, fair value	164,661
Fair Value, Measurements, Recurring | Level 2 | Corporate bonds
Financial Assets:
Financial assets, fair value			3,732
Fair Value, Measurements, Recurring | Level 2 | Commercial paper
Financial Assets:
Financial assets, fair value			23,641
Fair Value, Measurements, Recurring | Level 3
Financial Assets:
Liabilities, fair value	29,500
Fair Value, Measurements, Recurring | Forward Contract Liability
Financial Assets:
Liabilities, fair value	164,382
Fair Value, Measurements, Recurring | Forward Contract Liability | Level 2
Financial Assets:
Liabilities, fair value	164,382
Fair Value, Measurements, Recurring | Parapyre Option Obligation
Financial Assets:
Liabilities, fair value	279
Fair Value, Measurements, Recurring | Parapyre Option Obligation | Level 2
Financial Assets:
Liabilities, fair value	279
Fair Value, Measurements, Recurring | CVR Liability
Financial Assets:
Liabilities, fair value	29,500
Fair Value, Measurements, Recurring | CVR Liability | Level 3
Financial Assets:
Liabilities, fair value	29,500
Fair Value, Measurements, Recurring | Money market funds
Financial Assets:
Financial assets, fair value	18,861		15,250
Fair Value, Measurements, Recurring | Money market funds | Level 1
Financial Assets:
Financial assets, fair value	$ 18,861		15,250
Fair Value, Measurements, Recurring | U.S. Government Securities
Financial Assets:
Financial assets, fair value			4,230
Fair Value, Measurements, Recurring | U.S. Government Securities | Level 2
Financial Assets:
Financial assets, fair value			$ 4,230

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)			3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 22, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in fair value of forward contract liability	$ 58,200,000		$ 58,170,000	$ 0	$ 58,170,000	$ 0
Stock-based compensation					3,620,000	$ 4,118,000
Financial liabilities outstanding measured at fair value								$ 0
Forward Contract Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of forward contract	$ 164,400,000	$ 106,200,000	164,400,000		164,400,000
Parapyre Option Obligation
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Pro-rated estimated fair value of options					300,000
Fair value of Parapyre Options assumed		$ 100,000			100,000
Stock-based compensation			$ 200,000		$ 200,000
Parapyre Option Obligation | Forecast
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of annual equity grant of options							1%
Series A Preferred Stock | Asset Acquisition
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Asset acquisition consideration transferred equity interest issued, shares		364,887

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Significant Inputs Used to Estimate the Fair Value (Details) - CVR Liability - Level 3	6 Months Ended
	Jun. 30, 2023
Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated cash flow dates	Jun. 22, 2026
Estimated probability of success	100%
Risk-adjusted discount rates	7.94%
Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated cash flow dates	Nov. 28, 2023
Estimated probability of success	27%
Risk-adjusted discount rates	7.37%

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Changes in CVR Liability (Details)	6 Months Ended
	Jun. 30, 2023 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance as of December 31, 2022	$ 0
CVR Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance as of December 31, 2022	0
Fair value at CVR issuance	29,500,000
Ending Balance as of June 30, 2023	$ 29,500,000

Cash Equivalents and Marketab_3

Cash Equivalents and Marketable Securities - Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	$ 18,861	$ 26,007
Cash equivalents,Gross Unrealized Gains	0	1
Cash equivalents, gross unrealized losses	0	(3)
Cash equivalents, estimated fair value	18,861	26,005
Marketable securities, amortized cost		20,877
Marketable securities, gross unrealized gains		2
Marketable securities, gross unrealized losses		(31)
Marketable securities, estimated fair value	0	20,848
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	18,861	15,250
Cash equivalents,Gross Unrealized Gains	0	0
Cash equivalents, gross unrealized losses	0	0
Cash equivalents, estimated fair value	$ 18,861	15,250
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost		7,021
Cash equivalents,Gross Unrealized Gains		1
Cash equivalents, gross unrealized losses		(2)
Cash equivalents, estimated fair value		7,020
Marketable securities, amortized cost		16,644
Marketable securities, gross unrealized gains		2
Marketable securities, gross unrealized losses		(25)
Marketable securities, estimated fair value		16,621
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost		3,738
Marketable securities, gross unrealized gains		0
Marketable securities, gross unrealized losses		(6)
Marketable securities, estimated fair value		3,732
U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost		3,736
Cash equivalents,Gross Unrealized Gains		0
Cash equivalents, gross unrealized losses		(1)
Cash equivalents, estimated fair value		3,735
Marketable securities, amortized cost		495
Marketable securities, gross unrealized gains		0
Marketable securities, gross unrealized losses		0
Marketable securities, estimated fair value		$ 495

Cash Equivalents and Marketab_4

Cash Equivalents and Marketable Securities - Schedule of Gross Unrealized Losses and Fair Value by Investment Category and Age (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 25,166
Less than 12 Months, Unrealized Losses	(34)
12 Months or Longer, Fair Value	0
12 Months or Longer, Unrealized Losses	0
Total, Fair Value	25,166
Total, Unrealized Losses	(34)
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	17,699
Less than 12 Months, Unrealized Losses	(27)
12 Months or Longer, Fair Value	0
12 Months or Longer, Unrealized Losses	0
Total, Fair Value	17,699
Total, Unrealized Losses	(27)
U.S. government securities
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	3,735
Less than 12 Months, Unrealized Losses	(1)
12 Months or Longer, Fair Value	0
12 Months or Longer, Unrealized Losses	0
Total, Fair Value	3,735
Total, Unrealized Losses	(1)
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	3,732
Less than 12 Months, Unrealized Losses	(6)
12 Months or Longer, Fair Value	0
12 Months or Longer, Unrealized Losses	0
Total, Fair Value	3,732
Total, Unrealized Losses	$ (6)

Cash Equivalents and Marketab_5

Cash Equivalents and Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
US Government Agencies Debt Securities
Cash Equivalents And Marketable Securities [Line Items]
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	100,000		100,000		100,000
U.S. Banking Institution
Cash Equivalents And Marketable Securities [Line Items]
Cash	215,600,000		215,600,000		$ 23,500,000
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 - Summary of Contractual Maturities of Marketable Securities at Estimated Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 0	$ 20,848
Due thereafter	0	0
Total marketable securities	$ 0	$ 20,848

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Accrued Liabilities And Other Liabilities [Abstract]
Accrued financing fees for the PIPE	$ 12,677	$ 0
Accrued compensation	7,240	4,589
Accrued contracted research and development costs	4,450	6,972
Accrued professional and consulting fees	3,674	946
Accrued other	386	330
Total accrued and other current liabilities	$ 28,427	$ 12,837

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jun. 22, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2023	Jul. 12, 2023
Related Party Transaction [Line Items]
Stock compensation expense				$ 3,620,000	$ 4,118,000
Parapyre Option Obligation
Related Party Transaction [Line Items]
Stock compensation expense		$ 200,000		200,000
Parapyre Option Obligation | Forecast
Related Party Transaction [Line Items]
Percentage of annual equity grant of options						1%
Paragon Agreement
Related Party Transaction [Line Items]
Related party expenses incurred prior to asset acquisition	$ 19,300,000
Related party expenses unpaid prior to asset acquisition	19,300,000
Research initiation fees	3,000,000
Reimbursable research costs	$ 16,300,000
Cash payments made to Paragon		$ 0	$ 0	$ 0	$ 0
Paragon
Related Party Transaction [Line Items]
Percentage of ownership		5%		5%
Paragon | SPY001 License Agreement | Maximum | Subsequent Event
Related Party Transaction [Line Items]
Contingent obligation based on milestones							$ 22,000,000
Fairmount Funds Management LLC
Related Party Transaction [Line Items]
Percentage of ownership		5%		5%
Percentage of ownership held in third party		5%		5%

Related Party Transactions - Su

Related Party Transactions - Summary of Expenses Related to Paragon and Settled in Cash (Details) - Paragon Agreement - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Related Party Transaction [Line Items]
Reimbursable costs	$ 1.2
Paragon | Research and Development
Related Party Transaction [Line Items]
Reimbursable costs		$ 1.2	$ 0	$ 1.2	$ 0

Related Party Transactions - _2

Related Party Transactions - Summary of Related party Accounts Payable (Details) - Parapyre - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Total related party accounts payable	$ 20.8	$ 0
Reimbursable costs under the Paragon Agreement
Related Party Transaction [Line Items]
Total related party accounts payable	20.5	0
Parapyre Option Obligation Liability
Related Party Transaction [Line Items]
Total related party accounts payable	$ 0.3	$ 0

Asset Acquisition - Additional

Asset Acquisition - Additional Information (Details) $ / shares in Units, $ in Millions	Jun. 22, 2023 USD ($) $ / shares shares
Asset Acquisition [Line Items]
Cost to acquire asset | $	$ 113.3
Asset Acquisition
Asset Acquisition [Line Items]
Asset acquisition consideration transferred issuable shares of common stock on an as-converted basis	364,887,000
Spyre 2023 Equity Incentive Plan | Asset Acquisition
Asset Acquisition [Line Items]
Outstanding and unexercised stock options	68,365
Series A Preferred Stock | Asset Acquisition
Asset Acquisition [Line Items]
Asset acquisition consideration transferred equity interest issued, shares	364,887
Shares issued, price per share | $ / shares	$ 291.08
Common Stock | Asset Acquisition
Asset Acquisition [Line Items]
Asset acquisition consideration transferred equity interest issued, shares	12,945,385
Shares issued, price per share | $ / shares	$ 0.29108

Asset Acquisition - Schedule of

Asset Acquisition - Schedule of Asset Acquisition Cost (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 22, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Asset Acquisition [Line Items]
Assumed liabilities	$ 20,200
Transaction costs incurred by Aeglea	3,200
Fair value of Parapyre Options assumed by Aeglea	100
Acquired in-process research and development	130,500	$ 130,486	$ 0	$ 130,486	$ 0
Cash acquired	(3,000)			$ (3,035)
Total cost to acquire asset	113,300
Series A Preferred Stock and common stock
Asset Acquisition [Line Items]
Consideration transferred	$ 110,000

Series A Non-Voting Convertib_2

Series A Non-Voting Convertible Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 07, 2023	Jun. 26, 2023	Jun. 22, 2023	Jun. 30, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Authorized issuance shares of Series A Preferred Stock				8,913,659	10,000,000
Preferred Stock, par value				$ 0.0001	$ 0.0001
Series A Preferred Stock
Class of Stock [Line Items]
Authorized issuance shares of Series A Preferred Stock			1,086,341
Preferred Stock, par value			$ 0.0001
Preferred stock issued and outstanding percentage			30%
Conversion basis			1,000
Preferred stock, redemption value				$ 325
Preferred stock, redemption per share				$ 0.4505
Series A Preferred Stock | Asset Acquisition | Subsequent Event
Class of Stock [Line Items]
Asset acquisition consideration transferred equity interest issued, shares	364,887
Series A Preferred Stock | Minimum
Class of Stock [Line Items]
Beneficially holders owned percentage			0%
Series A Preferred Stock | Maximum
Class of Stock [Line Items]
Beneficially holders owned percentage			19.99%
Series A Preferred Stock | Private Placement
Class of Stock [Line Items]
Number of shares		721,452
Gross proceeds of shares		$ 210
Net related proceeds		$ 197.3

Paragon Agreement - Additional

Paragon Agreement - Additional Information (Details) - USD ($)				3 Months Ended		6 Months Ended
	Jul. 12, 2023	Jun. 30, 2023	Jun. 22, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2023
Parapyre Option Obligation | Forecast
Related Party Transaction [Line Items]
Percentage of annual equity grant of options								1%
Paragon Agreement
Related Party Transaction [Line Items]
Reimbursable costs		$ 1,200,000
Reimbursable research costs			$ 16,300,000
Payments to Paragon				$ 0	$ 0	$ 0	$ 0
Related party expenses incurred prior to asset acquisition			19,300,000
Research initiation fees			3,000,000
Related party expenses unpaid prior to asset acquisition			19,300,000
Paragon
Related Party Transaction [Line Items]
Nonrefundable research initiation fee for one program paid in cash			800,000
Paragon | Paragon Agreement
Related Party Transaction [Line Items]
Reimbursable research costs			16,300,000
Research initiation fees			$ 3,000,000
Paragon | SPY001 License Agreement | Subsequent Events
Related Party Transaction [Line Items]
Nomination fee	$ 1,500,000
First milestone payment	2,500,000
Paragon | SPY001 License Agreement | Subsequent Events | Maximum
Related Party Transaction [Line Items]
Contingent obligation based on milestones	$ 22,000,000

Liabilities, Convertible Pref_3

Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity - Additional Information (Details) - USD ($)			1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 22, 2023	Jan. 01, 2023	May 31, 2022	Jul. 31, 2020	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Aug. 04, 2023	Jan. 01, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants to purchase shares			17,372,312
Offering price of warrant			$ 1.5999
Exercise price per warrant			$ 0.0001
Net proceeds from sale of common stock			$ 42,900,000
Placement agent fees and offering costs			$ 2,100,000
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%
Period after notice received by company maximum ownership percentage to be effective description							The revised Maximum Ownership Percentage would be effective 61 days after the notice is received by the Company.
Stock-based compensation expense					$ 1,911,000	$ 2,018,000	$ 3,620,000	$ 4,118,000
Options granted					63,417,415	429,000
Stock-based compensation							$ 3,620,000	$ 4,118,000
Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Pre-funded warrants exercised									7,031,250
2016 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual percentage of additional shares		4%
Additional number of shares available for issuance		2,614,013								1,974,205
Common stock available for future issuance					5,384,315		5,384,315
Expense on contingent awards					$ 0		$ 0
Stock options granted to certain members of board of directors, contingent on stockholder approval	68,000,955
2016 Equity Incentive Plan | Restricted Stock Units RSU
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, granted to employees				228,200
Stock-based compensation expense							$ 0
2016 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option to purchase an aggregate of common stock shares							44,816	64,743
Aggregate cash proceeds from sale of shares								$ 200,000
2018 Equity Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional number of shares available for grant	70,000,000
Vest period grant date	4 years
Exercise period grant date	10 years
Exercise price	$ 0.30
Options granted	63,417,415
Spyre 2023 Equity Incentive Plan | Asset Acquisition
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding and unexercised stock options	68,365
Parapyre Option Obligation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unamortized expense					1,300,000		$ 1,300,000
Annual percentage of additional shares	1%
Stock-based compensation					$ 200,000		200,000
Fair value of Parapyre Options assumed	$ 100,000						100,000
Pro-rated estimated fair value of options							$ 300,000
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum ownership percentage of common stock shares for outstanding warrants to be exercised							19.99%
Maximum | 2016 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate cash proceeds from sale of shares							$ 100,000
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued			10,752,688
Public offering price			$ 1.60

Liabilities, Convertible Pref_4

Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity - Summary of Pre-funded Warrants for Common Stock Issued and Outstanding (Details) - $ / shares	6 Months Ended
	Jun. 30, 2023	May 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise Price		$ 0.0001
Pre-funded Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Warrants Outstanding	13,281,250
Pre-funded Warrants | February 8, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issue Date	Feb. 08, 2019
Expiration Date	None
Exercise Price	$ 0.0001
Number of Warrants Outstanding	0
Pre-funded Warrants | April 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issue Date	Apr. 30, 2020
Expiration Date	None
Exercise Price	$ 0.0001
Number of Warrants Outstanding	0
Pre-funded Warrants | May 20, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issue Date	May 20, 2022
Expiration Date	None
Exercise Price	$ 0.0001
Number of Warrants Outstanding	13,281,250

Liabilities, Convertible Pref_5

Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity - Schedule of Company's Stock Awards Granted (Details) - $ / shares	3 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Grants	63,417,415	429,000
Weighted Average Grant Date Fair Value	$ 0.30	$ 0.96

Liabilities, Convertible Pref_6

Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,911	$ 2,018	$ 3,620	$ 4,118
Research and Development
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	394	691	1,171	1,392
General and Administrative
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,517	$ 1,327	$ 2,449	$ 2,726

Liabilities, Convertible Pref_7

Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity - Schedule of Estimate Fair Value of Stock Options Granted (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
2016 Equity Incentive Plan
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term (in years)	6 years 10 days	5 years 11 months 23 days	6 years 10 days	6 years 3 days
Expected volatility	117%	82%	115%	82%
Risk-free interest	3.98%	2.96%	3.99%	2.07%
Dividend yield	0%	0%	0%	0%
2016 Employee Stock Purchase Plan
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Expected term (in years)	0 years	0 years	5 months 26 days	5 months 26 days
Expected volatility	0%	0%	181%	76%
Risk-free interest	0%	0%	4.99%	1.09%
Dividend yield	0%	0%	0%	0%

Strategic License Agreements -

Strategic License Agreements - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended				6 Months Ended
	Jul. 31, 2021	Jun. 30, 2021	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2021	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Research And Development Arrangement Contract To Perform For Others [Line Items]
Revenue recognized			$ 688		$ 625		$ 886	$ 1,987
Current deferred revenue			930				930		$ 517
Contract liabilities			3,271				3,271		$ 2,696
Contract assets			0		0		0	0
Immedica Pharma AB
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research agreement date				2021-03
Non refundable payment received						$ 21,500
Percentage of payment for cost incurred in PIP trial						50%
Rate of revenue share						25%
Reimbursement	$ 3,000
Upfront payment						$ 21,500
Modified transaction price	25,100
Estimated amount incurred	$ 3,600
Allocation price net						12,000
Total deferred revenue			3,300		2,700		3,300	2,700
Current deferred revenue			900		300		900	300
Immedica Pharma AB | Peace Phase 3 Trial and Drug Supply
Research And Development Arrangement Contract To Perform For Others [Line Items]
Revenue recognized			$ 700				$ 900
Immedica Pharma AB | PEACE Trial and BLA Package
Research And Development Arrangement Contract To Perform For Others [Line Items]
Allocated amount of transaction price						9,600
Revenue recognized					$ 600			$ 2,000
Immedica Pharma AB | PIP Trial
Research And Development Arrangement Contract To Perform For Others [Line Items]
Allocated amount of transaction price						$ 3,500
Immedica Pharma AB | License Agreements
Research And Development Arrangement Contract To Perform For Others [Line Items]
Revenue recognized		$ 12,000
Immedica Pharma AB | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Percentage of payment for cost incurred in PIP trial						50%
Costs incurred in performing PIP the trial						$ 1,800

Strategic License Agreements _2

Strategic License Agreements - Summary of Changes in Contract Liabilities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2023 USD ($)
Change in Contract with Customer, Liability [Abstract]
Beginning Balance	$ 2,696
Additions	628
Deductions	(53)
Ending Balance	$ 3,271

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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
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	16,363,183	8,566,549	13,937,881	8,113,849
Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		181,500	9,519	186,243
Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	39,640,000		19,930,000

Restructuring Charges - Additio

Restructuring Charges - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Employee workforce, termination percentage	83%
Cash severance payments and other employee-related costs	$ 6.4
Cash payments for employee related restructuring charges	2.2
Non-cash stock-based compensation expense related to accelerated vesting of stock-based awards	1
Total consideration from disposal of long lived assets	$ 0.5
Lease abandonment effective date	Jun. 30, 2023
Impairment loss operating lease right-of-use asset	$ 0.9
Impairment on leasehold improvements	1.7
Research and Development
Restructuring Cost and Reserve [Line Items]
Loss on disposal of long-lived assets	0.7
General and Administrative
Restructuring Cost and Reserve [Line Items]
Loss on disposal of long-lived assets	$ 0.2

Restructuring Charges - Summary

Restructuring Charges - Summary of Accrued Restructuring Balance (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Payments	$ (2,200)
Severance Liability
Restructuring Cost and Reserve [Line Items]
Beginning Balance December 31, 2022	0
Charges	6,448
Payments	(2,200)
Ending Balance June 30, 2023	$ 4,248

Restructuring Charges - Summa_2

Restructuring Charges - Summary of Charges Related to the Restructuring Activities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Restructuring Cost and Reserve [Line Items]
Severance and related			$ 6,400
Stock compensation	$ 1,911	$ 2,018	3,620	$ 4,118
Loss on disposal of long lived assets			915
Lease asset impairment			900
Research and Development
Restructuring Cost and Reserve [Line Items]
Stock compensation	394	691	1,171	1,392
General and Administrative
Restructuring Cost and Reserve [Line Items]
Stock compensation	$ 1,517	$ 1,327	2,449	$ 2,726
Restructuring Activities
Restructuring Cost and Reserve [Line Items]
Severance and related			6,448
Stock compensation			993
Loss on disposal of long lived assets			931
Lease asset impairment			2,580
Total Restructuring Costs			10,952
Restructuring Activities | Research and Development
Restructuring Cost and Reserve [Line Items]
Severance and related			3,182
Stock compensation			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 and related			3,266
Stock compensation			870
Loss on disposal of long lived assets			182
Lease asset impairment			1,175
Total Restructuring Costs			$ 5,493

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Events - USD ($) $ in Millions	Aug. 07, 2023	Jul. 27, 2023
Subsequent Event [Line Items]
Proceeds from upfront cash		$ 15
Termination fee	$ 2
Maximum
Subsequent Event [Line Items]
Contingent milestone payment		$ 100