144 0001691005 XXXXXXXX LIVE 0001818794 Dyne Therapeutics, Inc. 001-39509 1560 Trapelo Road Waltham MA 02451 (781)-786-8230 Susanna High Chief Operating Officer Common Stock Stifel Financial Corporation

3 Bryant Park, 4th Floor 1095 Avenue of the Americas New York NY 10036

9939 73513 61375598 11/02/2023 NASDAQ Common Stock 09/10/2023 Restricted stock units granted pursuant to Issuer's 2020 Stock Incentive Plan, subject to vesting requirements Issuer N 3635 09/10/2023 N/A Common Stock 09/17/2023 Restricted stock units granted pursuant to Issuer's 2020 Stock Incentive Plan, subject to vesting requirements Issuer N 6304 09/17/2023 N/A N Susanna High

1560 Trapelo Road Waltham MA 02451

Common Stock 09/12/2023 1635 17020 Susanna High

1560 Trapelo Road Waltham MA 02451

Common Stock 09/18/2023 2672 25144 The sales reported in this Form 144 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on July 10, 2023. Securities sold during the past three months represent shares automatically sold by the Reporting Person to satisfy tax withholding obligations in connection with the vesting of restricted stock units granted to the Reporting Person on September 17, 2020, December 10, 2021 and December 9, 2022. 11/02/2023 07/10/2023 /s/ Richard Scalzo, Attorney-in-Fact