As filed with the Securities and Exchange Commission on August 27, 2024

Registration No. 333-281690

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1

to

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Tectonic Therapeutic, Inc.

(Exact name of registrant as specified in its charter)

2019 Equity Incentive Plan

2024 Equity Incentive Plan

2024 Employee Stock Purchase Plan

(Full titles of the plans)

Daniel Lochner

Chief Financial Officer

490 Arsenal Way

Suite 210

Watertown, MA 02472

(339) 666-3320

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Marc A. Recht

Courtney T. Thorne

Katherine Denby

Cooley LLP

500 Boylston Street, 14^th Floor

Boston, MA 02116

(617) 937-2300

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

EXPLANATORY NOTE

This Post-Effective Amendment No. 1 (the “Amendment”), which relates to the Registration Statement filed on Form S-8, File No. 333-281690 (the “Original Registration Statement”) filed with the Securities and Exchange Commission on August 21, 2024 by Tectonic Therapeutic, Inc., a Delaware corporation (the “Registrant”), is being filed solely to file a Consent of Ernst & Young LLP, independent registered public accounting firm of AVROBIO, Inc. attached as Exhibit 23.2 hereto. Except as described herein, this Amendment does not update, amend or modify any other information, statement or disclosure contained in the Original Registration Statement, and all other portions of the Original Registration Statement, as previously filed, remain unchanged. No additional securities are to be registered, and registration fees were paid upon filing of the Original Registration Statement.

1

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Post Effective Amendment No. 1 to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Watertown, Commonwealth of Massachusetts, on August 27, 2024.

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement on Form S-8 has been signed by the following persons in the capacities and on the dates indicated.

2

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in this Registration Statement on Form S-8/A of our report dated April 12, 2024 relating to the financial statements of Tectonic Therapeutic, Inc. appearing in the Current Report on Form 8-K filed on June 20, 2024 for the year ended December 31, 2023.

Exhibit 23.2

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in Amendment No. 1 to the Registration Statement (Form S-8 No. 333-281690) pertaining to the 2019 Equity Incentive Plan, 2024 Equity Incentive Plan, and 2024 Employee Stock Purchase Plan of Tectonic Therapeutic, Inc. of our report dated March 14, 2024, with respect to the consolidated financial statements of AVROBIO, Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2023, filed with the Securities and Exchange Commission.