Tectonic Therapeutic Inc. 美股招股说明书（2025-05-19版）

Tectonic Therapeutic, Inc. Up to 2,969,583 Shares of Common Stock This prospectus supplement supplements the prospectus dated April3, 2025 (the “Prospectus”), which forms a part of our registration statementon FormS-1(No.333-280909),as amended. This prospectus supplement is being filed to update and supplement the information in the Prospectus withcertain information contained in our Quarterly Report on Form8-K,filed with the Securities and Exchange Commission on May19, 2025 (the “Current The Prospectus and this prospectus supplement relate to the proposed offer and resale or other disposition from time to time by the sellingstockholders identified in this prospectus of up to an aggregate of 2,969,583 shares of common stock, par value $0.0001 per share (the “Common Our Common Stock is listed on the Nasdaq Global Market under the ticker symbol “TECX.” On May16, 2025, the last reported sales price of ourCommon Stock was $20.99 per share. This prospectus supplement should be read in conjunction with the Prospectus, including any amendments or supplements thereto, which is to bedelivered with this prospectus supplement. This prospectus supplement is qualified by reference to the Prospectus, including any amendments or This prospectus supplement is not complete without, and may not be delivered or utilized except in connection with, the Prospectus, including anyamendments or supplements thereto. Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described in the sectiontitled “Risk Factors” beginning on page 9 of the Prospectus, and under similar headings in any amendments or supplements to the Prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities, orpassed upon the accuracy or adequacy of this prospectus supplement or the Prospectus. Any representation to the contrary is a criminaloffense. Emerging growth company☐ Item 8.01Other Events. On May17, 2025, the Company issued a press release titled “Tectonic Therapeutic Presents Complete Results for Positive Phase 1b Clinical Trial ofTX45 in Patients with Group 2 Pulmonary Hypertension in HFpEF in Late-Breaking Presentation at ESC Heart Failure 2025.” A copy of the press Item 9.01Financial Statements and Exhibits.(d)Exhibits No.Description SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by theundersigned hereunto duly authorized. TECTONIC THERAPEUTIC, INC.