Material Agreement (Form 8-K)

On July 14, 2026, Q32 Bio Inc. (the "Company") entered into an underwriting agreement (the "Underwriting Agreement") with Morgan Stanley & Co. LLC, Jefferies LLC, Cantor Fitzgerald & Co. and Oppenheimer & Co. Inc., as representatives (the "Representatives") of the several underwriters named therein (the "Underwriters"), pursuant to which the Company agreed to issue and sell an aggregate of (i) 6,027,399 shares (the "Firm Shares") of its common stock, par value $0.0001 per share (the "Common Stock"), to the Underwriters at a price to the public of $18.25 per share and (ii) pre-funded warrants (the "Pre-Funded Warrants") to purchase up to 4,931,506 shares of Common Stock (such shares of Common Stock issuable upon exercise of the Pre-Funded Warrants, the "Pre-Funded Warrant Shares"), to the Underwriters at a public offering price of $18.2499 per Pre-Funded Warrant, which represents the per share public offering price less the $0.0001 per share exercise price for such Pre-Funded Warrant (the "Offering"). Pursuant to the Underwriting Agreement, the Company granted the underwriters a 30-day option to purchase up to an additional 1,643,835 shares of its Common Stock (the "Optional Shares," and together with the Firm Shares, the "Shares") at the public offering price, less underwriting discounts and commissions. All the Firm Shares and Pre-Funded Warrants in the Offering were sold by the Company.

The Offering is expected to close on July 16, 2026, subject to the satisfaction of customary closing conditions. The Company estimates that the net proceeds of this Offering, in each case after deducting underwriting discounts and commissions and estimated offering expenses, will be approximately $187.6 million, or $215.8 million if the Underwriters exercise in full their option to purchase the Optional Shares. The Company intends to use the net proceeds from the Offering for working capital purposes, including expenses related to research, clinical development and commercialization efforts including for supporting the advancement of bempikibart into future clinical trials.

Each Pre-Funded Warrant will be exercisable for one share of Common Stock at an exercise price of $0.0001 per share, or alternatively, at the election of each holder, shares of Common Stock will be issued through a cashless exercise, with the net number of shares of Common Stock determined according to the formula set forth in each Pre-Funded Warrant. The Pre-Funded Warrants are exercisable at any time after the date of issuance and will expire when exercised in full. A holder of a Pre-Funded Warrant may not exercise such Pre-Funded Warrant if the holder, together with its affiliates, would beneficially own more than 4.99% or 9.99%, as applicable, of the number of shares of Common Stock outstanding immediately after giving effect to such exercise (the "Ownership Limit"). Upon 61 days' prior notice from the holder to the Company, the holder may increase or decrease the Ownership Limit to any other percentage (not in excess of 19.99%).

The Company does not intend to list the Pre-Funded Warrants on the Nasdaq Capital Market, any other national securities exchange or any other nationally recognized trading system. The foregoing summary of the Pre-Funded Warrant does not purport to be complete and is qualified in its entirety by reference to the form of Pre-Funded Warrant, a copy of which is filed as Exhibit 4.1 to this Current Report on Form 8-K (the "Report") and incorporated herein by reference.

The Underwriting Agreement contains customary representations and warranties, conditions to closing, market standoff provisions, termination provisions and indemnification obligations, including for liabilities under the Securities Act of 1933, as amended. The representations, warranties and covenants contained in the Underwriting Agreement were made only for purposes of such agreement and as of specific dates, were solely for the benefit of the parties to such agreement, and may be subject to limitations agreed upon by such parties. The Underwriting Agreement is filed as Exhibit 1.1 to this Report and is incorporated herein by reference, and the foregoing description of the terms of the Underwriting Agreement does not purport to be complete and is qualified in its entirety by reference to such exhibit.

The Offering was made pursuant to a shelf registration statement on Form S-3 (File No. 333-297027) that was initially filed by the Company with the Securities and Exchange Commission (the "SEC") on June 25, 2026 and declared effective by the SEC on July 13, 2026 and a final prospectus supplement dated July 14, 2026.

A copy of the opinion of Goodwin Procter LLP, relating to the legality of the issuance and sale of the Shares, the Pre-Funded Warrants and the Pre-Funded Warrant Shares, is filed as Exhibit 5.1 to this Report.

This Report shall not constitute an offer to sell, or the solicitation of an offer to buy, the securities discussed herein, nor shall there be any sale of such securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.