[Form 4] Dyne Therapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Dyne Therapeutics insider sale tied to RSU vesting. John Cox, CEO & President and a director, reported on Form 4 an automatic sale of 2,640 shares of Dyne Therapeutics common stock on 09/05/2025 at a price of $13.41 per share to satisfy tax withholding obligations arising from the vesting of restricted stock units granted December 4, 2024. After the sale, the filing shows the Reporting Person beneficially owned 199,539 shares directly and has 72,000 shares held indirectly in four trusts for children.

The filing discloses the sale was pursuant to a binding RSU agreement consistent with a Rule 10b5-1 affirmative defense and that 2,640 shares were matchable under Section 16(b) to a 100,000-share purchase on 07/14/2025. The Reporting Person paid the issuer $11,565.07 representing the profit deemed realized under Section 16(b). The report was signed by an attorney-in-fact on 09/09/2025.

Positive

• Transaction used a binding RSU agreement consistent with a Rule 10b5-1 affirmative defense, improving compliance clarity
• Section 16(b) short-swing profit was paid to the issuer: $11,565.07, addressing potential disgorgement obligations
• Detailed holdings disclosed, including direct ownership of 199,539 shares and indirect trusts holding 72,000 shares

Negative

• 2,640 shares were matchable under Section 16(b) to a prior purchase, generating a short-swing profit
• Contains 118,057 unvested RSUs, indicating a substantial portion of equity subject to future vesting conditions

Insights

Securities Compliance Analyst

TL;DR: Transaction appears procedural and compliant; tax-withholding RSU sale used a binding plan and Section 16(b) short-swing obligation was settled.

The Form 4 indicates an automatic disposition of 2,640 shares to cover tax withholding on vested RSUs, documented as a binding agreement consistent with Rule 10b5-1. The filer identified a Section 16(b) match to a prior 100,000-share purchase and remitted $11,565.07 to the issuer for the deemed short-swing profit, which addresses potential disgorgement obligations. The filing includes clear disclosure of direct and indirect holdings, including 118,057 unvested RSUs and four trusts holding 18,000 shares each for beneficiaries.

Corporate Governance Specialist

TL;DR: Insider sale is routine for RSU tax settlement; governance disclosure is specific and timely.

The report shows the CEO both as an officer and director and discloses the nature of indirect ownership through trusts for beneficiaries. The automatic sale mechanism and explicit identification of the Rule 10b5-1 affirmative defense improve transparency. Payment to the company for the Section 16(b) profit demonstrates adherence to insider trading rules. No other material transfers, grants, or derivative transactions are reported in this filing.

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

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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)
09/05/2025

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	09/05/2025		S(1)(2)		2,640	D	$13.41	199,539(3)	D
Common Stock								18,000	I	By Trust #1(4)
Common Stock								18,000	I	By Trust #2(4)
Common Stock								18,000	I	By Trust #3(4)
Common Stock								18,000	I	By Trust #4(4)

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 2,640 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 $11,565.07, representing the amount of the profit deemed realized in connection with the short-swing transaction under Section 16(b) of the Exchange Act.

3. Includes 118,057 unvested RSUs.

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

	/s/ Ron Caponigro, Attorney-in-Fact	09/09/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What shares did John Cox sell according to the DYN Form 4?

The filing reports an automatic sale of 2,640 shares of Dyne Therapeutics common stock on 09/05/2025 at $13.41 per share to satisfy tax withholding on vested RSUs.

Was the sale part of a planned trading arrangement for DYN insider John Cox?

Yes. The sale was pursuant to a restricted stock unit agreement described as a binding contract consistent with the Rule 10b5-1 affirmative defense.

Did the filing report any Section 16(b) short-swing issue for DYN?

Yes. 2,640 shares were matchable to a 100,000-share purchase on 07/14/2025, and the Reporting Person paid $11,565.07 representing the deemed profit.

How many DYN shares does John Cox beneficially own after the transaction?

The filing reports 199,539 shares beneficially owned following the reported transaction(s), plus 72,000 shares held indirectly in four trusts.

Were any derivative transactions disclosed in this Form 4 for DYN?

No derivative securities transactions are disclosed in Table II of the filing; only non-derivative common stock transactions and holdings are reported.