Tectonic Therapeutic, Inc.

FOR THE 2025 ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON JUNE 6, 2025

We have sent you this Proxy Statement and the enclosed Proxy Card because the Board of Directors (the “Board”) of Tectonic Therapeutic, Inc. (referred to herein as the “Company”, “Tectonic”, “we”, “us” or “our”) is soliciting your proxy to vote at our 2025 Annual Meeting of Stockholders (the “Annual Meeting”) to be held virtually on June 6, 2025, at 8:00 a.m. Eastern Time, by visiting www.virtualshareholdermeeting.com/TECX2025.

In addition to solicitations by mail, our directors, officers and regular employees, without additional remuneration, may solicit proxies by telephone, e-mail and personal interviews. We have also retained Broadridge Financial Solutions, Inc. (“Broadridge”) to solicit proxies on our behalf as well. All costs of solicitation of proxies will be borne by us. Brokers, custodians and fiduciaries will be requested to forward proxy soliciting material to the owners of stock held in their names, and we will reimburse them for their reasonableout-of-pocket expenses incurred in connection with the distribution of proxy materials.

The only outstanding voting securities of Tectonic are shares of common stock, $0.0001 par value per share (the “Common Stock”), of which there were 18,671,229 shares outstanding as of April 14, 2025 (the “Record Date”). The holders of a majority of the shares of common stock issued and outstanding and entitled to vote, present in person or represented by proxy, are required to hold the Annual Meeting.

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