As previously disclosed, on March 27, 2026, Q32 Bio Inc. (the "Company") entered into a Controlled Equity OfferingSM Sales Agreement (the "Sales Agreement") with Cantor Fitzgerald & Co. (the "Sales Agent"), with respect to an at-the-market offering program pursuant to which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock, par value $0.0001 per share (the "Common Stock"), through the Sales Agent. The Company previously filed a prospectus supplement with the Securities and Exchange Commission ("SEC") on March 27, 2026, relating to the offer and sale of shares of Common Stock having an aggregate offering price of up to $14,200,000 (the "Shares") pursuant to the Sales Agreement (the "Prior Prospectus Supplement"). As of the date hereof, the Company has sold an aggregate amount of $14,200,000 under the Prior Prospectus Supplement. Accordingly, the offering pursuant to the Prior Prospectus Supplement has been terminated and the Company will not make any further offer or saleof Shares pursuant to the Prior Prospectus Supplement.

On April 24, 2026, the Company filed an additional prospectus supplement relating to the offer and sale of shares of Common Stock having an aggregate offering price of up to $75,000,000 (the "Additional Shares") pursuant to the Sales Agreement. The Additional Shares to be offered and sold under the Sales Agreement, if any, will be offered and sold pursuant to the Company's shelf registration statement on Form S-3 (File No. 333-286491), which was filed with SEC on April 11, 2025 and declared effective by the SEC on April 21, 2025. Goodwin Procter LLP, counsel to the Company, has issued a legal opinion relating to the Additional Shares. A copy of such legal opinion, including the consent included therein, is attached as Exhibit 5.1 hereto.