Dyne Therapeutics (DYN) CEO discloses 2,662-share sale for RSU taxes

Rhea-AI Filing Summary

Dyne Therapeutics CEO and President, who is also a director, reported selling 2,662 shares of Common Stock on December 5, 2025 at a weighted average price of $20.72. The shares were automatically sold to satisfy tax withholding obligations tied to restricted stock units granted on December 4, 2024, under a restricted stock unit agreement that constitutes a binding contract consistent with the affirmative defense to liability under Rule 10b5-1, so the sale did not represent a discretionary trade.

After this transaction, the insider beneficially owns 196,877 shares directly, including 108,976 unvested RSUs, and 18,000 shares held in each of four trusts for the benefit of the reporting person’s children. The report notes that 2,662 shares were matchable under Section 16(b) with a prior purchase of 100,000 shares on July 14, 2025, and the reporting person has paid the issuer $31,111.88, representing the profit deemed realized on that short-swing transaction.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Cox John

(Last) (First) (Middle)

C/O DYNE THERAPEUTICS, INC.

1560 TRAPELO ROAD

(Street)

WALTHAM MA 02451

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Dyne Therapeutics, Inc. [ DYN ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	CEO & President

3. Date of Earliest Transaction (Month/Day/Year)
12/05/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	12/05/2025		S(1)(2)		2,662	D	$20.72(3)	196,877(4)	D
Common Stock								18,000	I	By Trust #1(5)
Common Stock								18,000	I	By Trust #2(5)
Common Stock								18,000	I	By Trust #3(5)
Common Stock								18,000	I	By Trust #4(5)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Represents 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 December 4, 2024. The automatic sale of the Reporting Person's shares is provided for in a restricted stock unit agreement constituting a "binding contract" consistent with the affirmative defense to liability under Rule 10b5-1 and the sale does not represent a discretionary trade by the Reporting Person.

2. The Reporting Person's sale of shares of Common Stock reported herein was matchable under Section 16(b) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), to the extent of 2,662 shares, with the Reporting Person's purchase of 100,000 shares on July 14, 2025. The Reporting Person has paid to the Issuer an aggregate amount of $31,111.88, representing the amount of the profit deemed realized in connection with the short-swing transaction under Section 16(b) of the Exchange Act.

3. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $20.58 to $20.96, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote of this Form 4.

4. Includes 108,976 unvested RSUs.

5. These shares are held in a trust for the benefit of a child of the Reporting Person.

	/s/ Ron Caponigro, Attorney-in-Fact	12/05/2025
	** Signature of Reporting Person	Date
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FAQ

What insider transaction did Dyne Therapeutics (DYN) report for its CEO?

The CEO and President reported selling 2,662 shares of Common Stock on December 5, 2025, as shown in Table I of the report.

Why were 2,662 Dyne Therapeutics shares sold by the CEO?

The 2,662 shares were automatically sold to satisfy tax withholding obligations in connection with the vesting of restricted stock units granted on December 4, 2024.

At what price were the Dyne Therapeutics shares sold?

The sale had a weighted average price of $20.72, with individual trades executed between $20.58 and $20.96, inclusive.

How many Dyne Therapeutics shares does the CEO own after the sale?

After the transaction, the insider beneficially owns 196,877 shares directly, including 108,976 unvested RSUs, and 18,000 shares in each of four trusts for the benefit of the reporting person’s children.

What Section 16(b) short-swing profit is mentioned in this report?

The sale of 2,662 shares was matchable under Section 16(b) with a prior purchase of 100,000 shares on July 14, 2025, and the reporting person has paid the issuer $31,111.88, representing the profit deemed realized on that short-swing transaction.

Was the CEO’s sale made under a Rule 10b5-1 plan or binding contract?

Yes. The shares were sold under a restricted stock unit agreement that constitutes a binding contract consistent with the affirmative defense to liability under Rule 10b5-1, and the sale does not represent a discretionary trade.