Sutro Biopharma Announces Inducement Grants Under Nasdaq Listing Rule 5635(c)(4)

Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), today announced that on December 15, 2025, the Compensation Committee of Sutro’s Board of Directors granted stock options to purchase 24,500 shares of Sutro common stock and 2,000 restricted stock units (RSUs) to new non-executive employees. The grants were made as an inducement material to the employees’ acceptance of employment with Sutro and were approved by the Compensation Committee of Sutro’s Board of Directors in accordance with Nasdaq Listing Rule 5635(c)(4).

The stock options and RSUs are subject to the terms and conditions of Sutro’s Amended and Restated 2021 Equity Inducement Plan. One-fourth of the total number of shares underlying the stock options will vest on the one-year anniversary of the employee’s hire date and monthly thereafter until fully vested on the fourth anniversary, subject to the employee’s continued service with Sutro on each such vesting date. One-fourth of the total number of shares subject to the RSUs will vest on the one-year anniversary of the employee’s hire date and annually thereafter until fully vested on the fourth anniversary, subject to the employee’s continued service with Sutro on each such vesting date.

About Sutro Biopharma

Sutro Biopharma, Inc. is advancing a next-generation antibody-drug conjugate (ADC) platform designed to deliver single- and dual-payload ADCs that enable meaningful breakthroughs for patients with cancer. By fully optimizing the antibody, linker, and payload, Sutro’s cell-free platform produces ADCs that are engineered to improve drug exposure, reduce side effects, and expand the range of treatable tumor types. With unique capabilities in dual-payload ADCs, Sutro aims to overcome treatment resistance and redefine what’s possible in cancer therapy. The Company’s pipeline of single- and dual-payload ADCs targets large oncology markets with limited treatment options and significant need for improved therapies. For more information, follow Sutro on social media @Sutrobio or visit www.sutrobio.com.

Investor Contact Emily White Sutro Biopharma (650) 823-7681 [email protected]

Media Contact Amy Bonanno Lyra Strategic Advisory [email protected]