UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

SCHEDULE 14A INFORMATION

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SUTRO BIOPHARMA, INC.

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SUTRO BIOPHARMA SUTRO BIOPHARMA, INC. 111 OYSTER POINT BOULEVARD SOUTH SAN FRANCISCO, CALIFORNIA 94080 Your Vote Counts! SUTRO BIOPHARMA, INC. 2022 Annual Meeting Vote by June 05, 2022 11 :59 PM ET You invested in SUTRO BIOPHARMA, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the shareholder meeting to be held on June 06, 2022. Get informed before you vote View the Notice & Proxy Statement, Form 1 0-K online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 23, 2022. If you would like to request a copy of the material(s) for this and/or future shareholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. Smartphone users Point your camera here and vote without entering a control number Vote Virtually at the Meeting* June 06, 2022 8:00AM PDT Virtually at: www.virtualshareholdermeeting.com/STR02022 *Please check the meeting materials for any special requirements for meeting attendance.

Vote at www.ProxyVote.com THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming shareholder meeting. Please follow the instructions on the reverse side to vote these important matters. Board Voting Items Recommends 1. Election of Directors Nominees: 01) Michael Dybbs, Ph.D. 02) John G. Freund, M.D. 03) Heidi Hunter 04) Jon Wigginton, M.D. For 2. To ratify the appointment of Ernst & Young LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2022. For 3. To approve, on a non-binding, advisory basis, the compensation of our named executive officers. For 4. To determine, on a non-binding, advisory basis, the frequency of future non-binding, advisory votes on the compensation of the Company's named executive officers. 1 Year NOTE: Such other business as may properly come before the meeting or any adjournment thereof. Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click "Sign up for E-delivery".