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The Company and Basis of Presentation (Details) $ / shares in Units, $ in Thousands |  |  |  |  |  |  |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended | 127 Months Ended |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 15, 2025 USD ($) $ / shares shares | Nov. 29, 2024 shares | May 14, 2024 shares | Apr. 23, 2024 $ / shares shares | Mar. 20, 2024 USD ($) $ / shares shares | Mar. 18, 2024 shares | Dec. 11, 2023 shares | Jun. 22, 2023 | Sep. 30, 2025 USD ($) $ / shares shares | Jun. 30, 2024 shares | Mar. 31, 2024 shares | Sep. 30, 2025 USD ($) segment $ / shares shares | Dec. 31, 2024 USD ($) $ / shares shares | Sep. 30, 2025 USD ($) $ / shares shares | Jun. 30, 2025 shares | Mar. 31, 2025 shares | Feb. 28, 2025 USD ($) | Sep. 30, 2024 shares | Sep. 06, 2024 USD ($) | Apr. 25, 2024 shares | Apr. 24, 2024 shares | Dec. 31, 2023 shares
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of operating segments | segment |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |
Proceeds from raising capital | $ |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  |  |  |  |  |  |  |
Accumulated deficit | $ |  |  |  |  |  |  |  |  | $ 1,065,105 |  |  | $ 1,065,105 | $ 972,432 | 1,065,105 |  |  |  |  |  |  |  |
Marketable securities | $ |  |  |  |  |  |  |  |  | $ 486,200 |  |  | $ 486,200 |  | $ 486,200 |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exchange of Series A non-voting convertible preferred stock into common stock (in shares) |  |  |  |  |  |  |  |  |  | 3,640,000 |  |  |  |  |  |  |  |  |  |  |  |
Shares converted (in shares) |  |  |  |  |  |  |  |  |  | 10,198,000 |  |  |  |  |  |  |  |  |  |  |  |
Conversion Of Series B Non-Voting Convertible Preferred Stock | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares converted (in shares) |  |  | 10,198,320 |  |  |  |  |  |  |  |  | 10,198,320 |  |  |  |  |  |  |  |  |  |
At-The-Market Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, authorized amount | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500,000 |  |  |
Common Stock and Series B Non Voting Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Series B non-voting convertible preferred stock, par value (in dollars per share) | $ / shares |  |  |  |  | $ 0.0001 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion basis |  |  |  |  | 40 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Series B Non Voting Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion basis |  |  |  |  | 40 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of non-voting convertible preferred stock (in shares) |  |  |  |  | 121,625 | 271,625 | 150,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  | $ 0.0001 |  |  | $ 0.0001 | $ 0.0001 | $ 0.0001 |  |  |  |  |  |  |  |
Preferred stock, outstanding (in shares) |  |  |  |  |  |  |  |  | 16,667 |  |  | 16,667 | 16,667 | 16,667 |  |  |  |  |  |  |  |
Preferred stock, not automatically converted, outstanding (in shares) |  |  |  |  |  |  |  |  | 16,667 |  |  | 16,667 |  | 16,667 |  |  |  |  |  |  |  |
Series B Non Voting Convertible Preferred Stock | Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of non-voting convertible preferred stock (in shares) |  |  |  |  |  |  |  |  |  |  | 122,000 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, outstanding (in shares) |  |  |  |  |  |  |  |  | 17,000 | 17,000 | 0 | 17,000 | 17,000 | 17,000 | 17,000 | 17,000 |  | 17,000 |  |  |  | 0
Shares converted (in shares) |  |  |  |  |  |  |  |  |  | (255,000) |  |  |  |  |  |  |  |  |  |  |  |
Series B Non Voting Convertible Preferred Stock | Conversion Of Series B Non-Voting Convertible Preferred Stock | Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares converted (in shares) |  |  | 254,958 |  |  |  |  |  |  |  |  | 254,958 |  |  |  |  |  |  |  |  |  |
Series B Non Voting Convertible Preferred Stock | Private Placement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, price per share (in dollars per share) | $ / shares |  |  |  |  | $ 1,480 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, proceeds received | $ |  |  |  |  | $ 168,900 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Placement agent and other offering costs | $ |  |  |  |  | $ 11,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Series A Non Voting Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  | $ 0.0001 |  |  | $ 0.0001 | $ 0.0001 | $ 0.0001 |  |  |  |  |  |  |  |
Exchange of Series A non-voting convertible preferred stock into common stock (in shares) |  |  |  | 90,992 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, outstanding (in shares) |  |  |  |  |  |  |  |  | 346,045 |  |  | 346,045 | 346,045 | 346,045 |  |  |  |  |  | 346,045 | 346,045 |
Series A Non Voting Convertible Preferred Stock | Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exchange of Series A non-voting convertible preferred stock into common stock (in shares) |  |  |  |  |  |  |  |  |  | (91,000) |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, outstanding (in shares) |  |  |  |  |  |  |  |  | 346,000 | 346,000 | 437,000 | 346,000 | 346,000 | 346,000 | 346,000 | 346,000 |  | 346,000 |  |  |  | 437,000
Series A Non Voting Convertible Preferred Stock | Conversion Of Series A Non-Voting Convertible Preferred Stock | Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares converted (in shares) |  |  |  | 90,992 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exchange of Series A non-voting convertible preferred stock into common stock (in shares) |  |  |  | 3,639,680 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock | At-The-Market Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, proceeds received | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ 20,500 |  |  |  |  |  |  |  |  |
Sale of stock, authorized amount | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500,000 |  |  |  |  |
Sale of stock, aggregate offering price | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |  |  |
Number of shares of common stock sold (in shares) |  |  |  |  |  |  |  |  | 0 |  |  |  | 777,432 |  |  |  |  |  |  |  |  |
Sale of stock, remaining authorized amount | $ |  |  |  |  |  |  |  |  | $ 179,100 |  |  | $ 179,100 |  | $ 179,100 |  |  |  |  |  |  |  |
Common Stock | At-The-Market Offering | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, aggregate offering price | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 179,100 |  | $ 179,100 |  |  |
Common Stock | October 2025 Underwritten Offering | Subsequent Events |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, price per share (in dollars per share) | $ / shares | $ 18.50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, proceeds received | $ | $ 296,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Placement agent and other offering costs | $ | $ 19,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares of common stock sold (in shares) | 17,094,594 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock | Over-Allotment Option |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares of common stock sold (in shares) |  | 1,091,250 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock | Over-Allotment Option | Subsequent Events |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares of common stock sold (in shares) | 2,229,729 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Spyre Therapeutics, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset acquisition, stockholder payment period (in years) |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset acquisition, cash payment, threshold period (in years) |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset Acquisition | Series A Non Voting Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Company and Basis of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) | $ / shares |  |  |  | $ 0.0001 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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