Item 2.03. Creation of a Direct Financial Obligation or an Obligation under an Off-BalanceSheet Arrangement of a Registrant.

On December 8, 2025 (the "Amendment Closing Date"), Dyne Therapeutics, Inc. (the "Company") entered into the First Amendment (the "First Amendment") to Loan and Security Agreement with Hercules Capital, Inc. ("Hercules"), in its capacity as administrative agent and collateral agent (the "Agent"), and certain other financial institutions party thereto as lenders (collectively, the "Lenders").

The First Amendment amended certain of the tranche sizes and funding milestone requirements under the Loan and Security Agreement, dated as of June 27, 2025 (the "Initial Loan Agreement" and, such Initial Loan Agreement as amended by the First Amendment, the "Loan Agreement"), by and among the Company, Hercules and the Lenders and permitted the Company to borrow, as of the Amendment Closing Date, a second term loan tranche in an aggregate principal amount of $50.0 million. Following entry into the First Amendment and the borrowing of the second term loan tranche, the Company has two additional term loan tranches it may borrow pursuant to the Loan Agreement, totaling up to $75.0 million, which are available subject to the achievement of specified clinical, regulatory and commercial milestones, and a final term loan tranche of up to $50.0 million, which is available subject to approval by the Lenders' investment committee in their discretion.

All unpaid principal and accrued and unpaid interest with respect to the amounts outstanding under the Loan Agreement are due and payable in full on July 1, 2030 (the "Maturity Date"). The outstanding principal balance bears interest at a floating interest rate per annum equal to the Wall Street Journal prime rate, subject to a floor of 7.50%, plus 2.45%. Accrued interest on the amounts outstanding under the Loan Agreement is payable monthly. The Company may make payments of interest only until July 1, 2028, which interest-only period may be extended until the Maturity Date upon the achievement of specified clinical, regulatory and commercial milestones. At the end of the interest-only period, the Company is required to begin repayment of the outstanding principal amounts in equal monthly installments (or, in a single installment, if the interest-only period has been extended to the Maturity Date). As collateral for the obligations under the Loan Agreement, the Company has granted to the Agent, for the benefit of the Lenders, a first-priority security interest in substantially all of its property, inclusive of intellectual property, subject to customary permitted liens and other exceptions set forth in the Loan Agreement.

The material terms of the Initial Loan Agreement were described in Item 1.01 of the Company's Current Report on Form 8-Kfiled with the Securities and Exchange Commission on June 30, 2025 (the "Initial Loan Agreement Form 8-K")and those terms are incorporated by reference into this Item 2.03. Such description of the Initial Loan Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Initial Loan Agreement that was filed as Exhibit 10.1 to the Initial Loan Agreement Form 8-K.