144: Filer Information

Filer CIK

0001780068

Filer CCC

XXXXXXXX

Is this a LIVE or TEST Filing?

LIVE

TEST

Submission Contact Information

Name

Phone

E-Mail Address

144: Issuer Information

Name of Issuer

Dyne Therapeutics, Inc.

SEC File Number

001-39509

Address of Issuer

1560 Trapelo Road
Waltham
MASSACHUSETTS
02451

Phone

7817868230

Name of Person for Whose Account the Securities are To Be Sold

Atlas Venture Associates XI, LP

See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.

Relationship to Issuer

Shareholder

144: Securities Information

Title of the Class of Securities To Be Sold

Name and Address of the Broker

Number of Shares or Other Units To Be Sold

Aggregate Market Value

Number of Shares or Other Units Outstanding

Approximate Date of Sale

Name the Securities Exchange

Common

Merrill Lynch
555 California Street
18th Floor
San Francisco � CA � 94104

1413

28288.26

165027119

04/21/2026

Nasdaq

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class

Date you Acquired

Nature of Acquisition Transaction

Name of Person from Whom Acquired

Is this a Gift?

Date Donor Acquired

Amount of Securities Acquired

Date of Payment

Nature of Payment *

Common

04/26/2019

Private Placement

Issuer

1413

04/26/2019

Cash

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller

Title of Securities Sold

Date of Sale

Amount of Securities Sold

Gross Proceeds

Atlas Venture Fund XI, LP
300 Technology Sq
8th Floor
Cambridge � MA � 02139

Common

04/20/2026

142571

2859490.52

Atlas Venture Opportunity Fund II, L.P.
300 Technology Sq
8th Floor
Cambridge � MA � 02139

Common

04/20/2026

71722

1438499.97

Atlas Venture Opportunity Fund I, L.P.
300 Technology Sq
8th Floor
Cambridge � MA � 02139

Common

04/20/2026

56355

1130290.09

Atlas Venture Associates XI, L.P.
300 Technology Sq
8th Floor
Cambridge � MA � 02139

Common

04/20/2026

1401

28099.31

144: Remarks and Signature

Remarks

Date of Notice

04/21/2026

Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1

03/19/2026

ATTENTION:

The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.

Signature

Ommer Chohan

144: Filer Information

Submission Contact Information

144: Issuer Information

144: Securities Information

144: Securities To Be Sold

144: Securities Sold During The Past 3 Months

144: Remarks and Signature

ATTENTION:

ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)

SEC Form 144 filed by Dyne Therapeutics Inc.