Organization and Principal Activities	12 Months Ended
Dec. 31, 2025
Disclosure Text Block [Abstract]
Organization and Principal Activities	1. Organization and Principal Activities Description of Business Sutro Biopharma, Inc. (the “Company”), is an oncology company developing site-specific and novel-format antibody drug conjugates, or ADCs. The Company was incorporated on April 21, 2003 and is headquartered in South San Francisco, California. Underwritten Offerings In April 2024, the Company closed an underwritten offering with BofA Securities, Inc., pursuant to which the Company issued and sold 1,447,876 shares of its common stock at an offering price of $51.79 per share. The gross proceeds from these sales were approximately $75.0 million, before deducting fees and offering expenses. On February 9, 2026, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Leerink Partners LLC and TD Securities (USA) LLC, as representatives of the several underwriters named therein (the “Underwriters”), pursuant to which the Company agreed to issue and sell 7,868,383 shares of its common stock (the “Shares”) to the Underwriters (the “February 2026 Offering”). The Shares were sold at an offering price of $13.98 per share. The gross proceeds from the February 2026 Offering were approximately $110.0 million, before deducting underwriting discounts and commissions and estimated February 2026 Offering expenses. Restructuring Plans On March 13, 2025, the Company announced the completion of a strategic portfolio review (the "March 2025 Restructuring Plan") resulting in the prioritization of the Company's three wholly-owned preclinical programs in the Company's next-generation ADC pipeline, beginning with the Company's potentially best-in-class exatecan ADC targeting Tissue Factor, STRO-004. As a result of the reprioritization, the Company deprioritized additional investment into the development of luveltamab tazevibulin, or STRO-002, and luvelta-related activities, principally across clinical and manufacturing functions. The Company will continue to explore outlicensing opportunities for luvelta. In addition, given the Company’s significant progress in fully externalizing its cell-free manufacturing to scale, the Company exited its internal GMP manufacturing facility at the end of 2025. On September 29, 2025, the Company announced further organizational restructuring to prioritize the advancement of its three preclinical ADC programs and its research and development collaborations (the "September 2025 Restructuring Plan", and, together with the March 2025 Restructuring Plan, the “Restructuring Plans”). Taken together, the March 2025 Restructuring Plan and the September 2025 Restructuring Plan resulted in a reduction in the Company’s workforce by approximately two-thirds. See Note 11 for additional information on the effect of the Restructuring Plans on the financial statements. Liquidity The Company has incurred significant losses and has negative cash flows from operations. As of December 31, 2025, there was an accumulated deficit of $978.0 million. Management expects to continue to incur additional substantial losses in the foreseeable future as a result of the Company’s research and development and other operational activities. As of December 31, 2025, the Company had unrestricted cash, cash equivalents and marketable securities of $141.4 million which are available to fund future operations. The Company will need to raise additional capital to support the completion of its research and development activities and to support its operations. The Company believes that its unrestricted cash, cash equivalents, and marketable securities as of December 31, 2025, together with the proceeds from the February 2026 Offering, will enable the Company to maintain its operations for a period of at least 12 months following the filing date of these financial statements. Reverse Stock Split On December 2, 2025, the Company filed a Certificate of Amendment to its Restated Certificate of Incorporation with the Secretary of State of the State of Delaware to implement a 1-for-10 reverse stock split (the “Reverse Stock Split”) of the Company’s common stock. The Reverse Stock Split was reflected on the Nasdaq Global Market beginning with the opening of trading on December 3, 2025 and did not alter the par value of the Common Stock, change the number of authorized shares, or modify any voting rights or other terms of the Common Stock. No fractional shares were issued in connection with the Reverse Stock Split and stockholders who were affected by a fractional share were rounded up to the nearest full share. In addition, a proportionate adjustment was made to the per share exercise price and the number of shares issuable upon the exercise of all outstanding stock options to purchase shares of Common Stock and the number of shares reserved for issuance pursuant to the Company’s equity incentive and inducement plans, and employee stock purchase plan. All share amounts and per share amounts disclosed in this Annual Report on Form 10-K have been adjusted retroactively to reflect the Reverse Stock Split for all periods presented.

Organization and Principal Activities

12 Months Ended

Dec. 31, 2025

1. Organization and Principal Activities

Description of Business

Sutro Biopharma, Inc. (the “Company”), is an oncology company developing site-specific and novel-format antibody drug conjugates, or ADCs. The Company was incorporated on April 21, 2003 and is headquartered in South San Francisco, California.

Underwritten Offerings

In April 2024, the Company closed an underwritten offering with BofA Securities, Inc., pursuant to which the Company issued and sold 1,447,876 shares of its common stock at an offering price of $51.79 per share. The gross proceeds from these sales were approximately $75.0 million, before deducting fees and offering expenses.

On February 9, 2026, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Leerink Partners LLC and TD Securities (USA) LLC, as representatives of the several underwriters named therein (the “Underwriters”), pursuant to which the Company agreed to issue and sell 7,868,383 shares of its common stock (the “Shares”) to the Underwriters (the “February 2026 Offering”). The Shares were sold at an offering price of $13.98 per share. The gross proceeds from the February 2026 Offering were approximately $110.0 million, before deducting underwriting discounts and commissions and estimated February 2026 Offering expenses.

Restructuring Plans

On March 13, 2025, the Company announced the completion of a strategic portfolio review (the "March 2025 Restructuring Plan") resulting in the prioritization of the Company's three wholly-owned preclinical programs in the Company's next-generation ADC pipeline, beginning with the Company's potentially best-in-class exatecan ADC targeting Tissue Factor, STRO-004. As a result of the reprioritization, the Company deprioritized additional investment into the development of luveltamab tazevibulin, or STRO-002, and luvelta-related activities, principally across clinical and manufacturing functions. The Company will continue to explore outlicensing opportunities for luvelta. In addition, given the Company’s significant progress in fully externalizing its cell-free manufacturing to scale, the Company exited its internal GMP manufacturing facility at the end of 2025.

On September 29, 2025, the Company announced further organizational restructuring to prioritize the advancement of its three preclinical ADC programs and its research and development collaborations (the "September 2025 Restructuring Plan", and, together with the March 2025 Restructuring Plan, the “Restructuring Plans”).

Taken together, the March 2025 Restructuring Plan and the September 2025 Restructuring Plan resulted in a reduction in the Company’s workforce by approximately two-thirds. See Note 11 for additional information on the effect of the Restructuring Plans on the financial statements.

Liquidity

The Company has incurred significant losses and has negative cash flows from operations. As of December 31, 2025, there was an accumulated deficit of $978.0 million. Management expects to continue to incur additional substantial losses in the foreseeable future as a result of the Company’s research and development and other operational activities.

As of December 31, 2025, the Company had unrestricted cash, cash equivalents and marketable securities of $141.4 million which are available to fund future operations. The Company will need to raise additional capital to support the completion of its research and development activities and to support its operations.

The Company believes that its unrestricted cash, cash equivalents, and marketable securities as of December 31, 2025, together with the proceeds from the February 2026 Offering, will enable the Company to maintain its operations for a period of at least 12 months following the filing date of these financial statements.

Reverse Stock Split

On December 2, 2025, the Company filed a Certificate of Amendment to its Restated Certificate of Incorporation with the Secretary of State of the State of Delaware to implement a 1-for-10 reverse stock split (the “Reverse Stock Split”) of the Company’s common stock. The Reverse Stock Split was reflected on the Nasdaq Global Market beginning with the opening of trading on December 3, 2025 and did not alter the par value of the Common Stock, change the number of authorized shares, or modify any voting rights or other terms of the Common Stock. No fractional shares were issued in connection with the Reverse Stock Split and stockholders who were affected by a fractional share were rounded up to the nearest full share. In addition, a proportionate adjustment was made to the per share exercise price and the number of shares issuable upon the exercise of all outstanding stock options to purchase shares of Common Stock and the number of shares reserved for issuance pursuant to the Company’s equity incentive and inducement plans, and employee stock purchase plan. All share amounts and per share amounts disclosed in this Annual Report on Form 10-K have been adjusted retroactively to reflect the Reverse Stock Split for all periods presented.