Material Event (Form 8-K)

As previously disclosed, on May 6, 2022, Cogent Biosciences, Inc. (the "Company") entered into a Sales Agreement with Guggenheim Securities, LLC ("Guggenheim Securities"), as amended by that certain Amendment No. 1 to Sales Agreement, dated November 7, 2025 (as amended, the "Sales Agreement"), pursuant to which the Company may offer and sell shares of the Company's common stock, par value $0.001 per share ("Common Stock"), at any time and from time to time through or to Guggenheim Securities, as sales agent or principal, at market prices by any method that is deemed to be an "at-the-market offering" as defined in Rule 415 under the Securities Act of 1933, as amended (the "Securities Act").

On August 10, 2026, the Company filed a prospectus supplement (the "Prospectus Supplement") pursuant to Rule 424(b) under the Securities Act with the U.S. Securities and Exchange Commission (the "SEC") relating to the offer and sale of up to $400,000,000 of shares of Common Stock (the "Shares") under the Sales Agreement. The Prospectus Supplement forms a part of the Company's automatic shelf registration statement on Form S-3ASR (File No. 333-291384), which was filed with the SEC on November 7, 2025 and became automatically effective upon filing.

Gibson, Dunn & Crutcher LLP, counsel to the Company, has issued a legal opinion relating to the Shares. A copy of such legal opinion, including the consent included therein, is attached as Exhibit 5.1 hereto.

The Shares are registered pursuant to the Registration Statement and the base prospectus contained therein, and offerings of the Shares will be made only by means of the Prospectus Supplement. This Current Report on Form 8-K shall not constitute an offer to sell or a solicitation of an offer to buy the Shares described herein, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities law of such state or jurisdiction.