Dyne CMO sells 5,035 shares to cover taxes

Dyne Therapeutics’ chief medical officer reported automatic, non-discretionary share sales to cover tax withholding on RSU vesting under Rule 10b5-1–style binding contracts.

Rhea-AI Filing Summary

Dyne Therapeutics, Inc. (DYN) reported that Chief Medical Officer Douglas Kerr sold a total of 5,035 shares of common stock in two transactions on September 4 and 8, 2026. The sales were automatically executed to satisfy tax withholding obligations triggered by vesting of restricted stock units.

The automatic sales occurred under restricted stock unit agreements constituting a “binding contract” consistent with the affirmative defense under Rule 10b5-1 and are described as non-discretionary. Following these transactions, Kerr continues to hold 125,126 unvested RSUs.

Insider Trade Summary 10b5-1

Net Seller: 5,035 shares

Net Sell 2 txns

Insider Kerr Douglas

Role Chief Medical Officer

Sold 5,035 shs ($116K)

Type	Security	Shares	Price	Value
Sale	Common Stock F3, F4, F5	1,290	$18.88	$24K
Sale	Common Stock F1, F2	3,745	$24.35	$91K

Holdings After Transaction: Common Stock — 162,564 shares (Direct)

Footnotes (5)

1. F1. 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 September 3, 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. F2. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $24.27 to $24.50, 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.
3. F3. 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.
4. F4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $18.77 to $18.92, 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.
5. F5. Includes 125,126 unvested RSUs.

Key Figures

Shares sold September 4, 2026: 3,745 shares Weighted average sale price September 4, 2026: $24.35 per share Shares sold September 8, 2026: 1,290 shares +3 more

6 metrics

Shares sold September 4, 2026 3,745 shares Common stock automatically sold to satisfy tax withholding on RSU vesting

Weighted average sale price September 4, 2026 $24.35 per share Multiple transactions within a range of $24.27 to $24.50

Shares sold September 8, 2026 1,290 shares Common stock automatically sold to satisfy tax withholding on RSU vesting

Weighted average sale price September 8, 2026 $18.88 per share Multiple transactions within a range of $18.77 to $18.92

Total shares sold 5,035 shares Aggregate of both automatic tax-withholding sales reported

Unvested RSUs held 125,126 RSUs Unvested restricted stock units remaining after the reported transactions

Key Terms

restricted stock units, Rule 10b5-1, weighted average price, tax withholding obligations

4 terms

restricted stock units financial

"in connection with the vesting of restricted stock units granted to the Reporting Person"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

Rule 10b5-1 regulatory

"constituting a "binding contract" consistent with the affirmative defense to liability under Rule 10b5-1"

Rule 10b5-1 is a regulation that allows company insiders to buy or sell their shares at predetermined times, even if they have access to non-public information. It acts like setting a schedule in advance for transactions, helping prevent accusations of unfair trading. This rule provides a way for insiders to plan trades transparently, giving investors confidence that these transactions are not based on hidden information.

weighted average price financial

"The price reported in Column 4 is a weighted average price."

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

tax withholding obligations financial

"sold by the Reporting Person to satisfy tax withholding obligations in connection with the vesting"

FAQ

What insider transactions did Dyne Therapeutics (DYN) disclose for Douglas Kerr?

The company disclosed that Chief Medical Officer Douglas Kerr sold 5,035 shares of Dyne Therapeutics common stock in two transactions on September 4 and 8, 2026, with both sales executed to satisfy tax withholding obligations related to vesting restricted stock units.

At what prices were the Dyne Therapeutics (DYN) shares sold by Douglas Kerr?

Kerr sold 3,745 shares at a weighted average price of $24.35 per share on September 4, 2026, and 1,290 shares at a weighted average price of $18.88 per share on September 8, 2026, in multiple trades within the stated price ranges.

Why did Douglas Kerr sell Dyne Therapeutics (DYN) shares in these transactions?

The sales represent shares automatically sold to satisfy tax withholding obligations arising from the vesting of restricted stock units granted on September 3, 2024 and December 4, 2024. The filing states these sales do not represent discretionary trades by Kerr.

Were Douglas Kerr’s Dyne Therapeutics (DYN) share sales under Rule 10b5-1 arrangements?

Yes. The RSU agreements are described as a “binding contract” consistent with the affirmative defense to liability under Rule 10b5-1, and the Form 4 indicates the transactions were made under an affirmative Rule 10b5-1 framework.

What Dyne Therapeutics (DYN) equity does Douglas Kerr continue to hold after these transactions?

After the reported sales, Kerr’s holdings include 125,126 unvested restricted stock units (RSUs). This figure is disclosed in a footnote describing his remaining RSU position; the Form 4 does not state his total number of common shares held.

How were the Dyne Therapeutics (DYN) sale prices for Douglas Kerr’s transactions determined?

For each date, the reported sale price is a weighted average price. On September 4, 2026, trades occurred between $24.27 and $24.50. On September 8, 2026, trades occurred between $18.77 and $18.92. Full breakdowns are available on request to the issuer or SEC staff.

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Available on EDGAR 09/08/2026 - 04:15 PM Accepted by SEC EDGAR 09/08/2026 - 04:14 PM Learn about SEC filing dates

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^*

Kerr Douglas

(Last) (First) (Middle)

C/O DYNE THERAPEUTICS, INC.

1560 TRAPELO ROAD

(Street)

WALTHAM MASSACHUSETTS 02451

(City) (State) (Zip)

UNITED STATES

(Country)

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

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

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Medical Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/04/2026

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

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

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

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	09/04/2026		S(1)		3,745	D	$24.35(2)	163,854	D
Common Stock	09/08/2026		S(3)		1,290	D	$18.88(4)	162,564(5)	D

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 September 3, 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 price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $24.27 to $24.50, 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.

3. 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.

4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $18.77 to $18.92, 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.

5. Includes 125,126 unvested RSUs.

	/s/ Ron Caponigro, Attorney-in-Fact	09/08/2026
	** 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.
* Form 4: SEC 1474 (03-26)