Dyne Therapeutics officer to sell 5,658 shares

An officer of Dyne Therapeutics has filed a Rule 144 notice for broker-assisted sales of company common stock, including shares underlying equity compensation awards.

Rhea-AI Filing Summary

Dyne Therapeutics, Inc. (DYN) has a notice under Rule 144 for planned sales of common stock held for the account of officer John Cox. A broker, Stifel Nicolaus & Company Inc., is named to sell 5,658 shares of common stock with an aggregate market value of $106,844.00, based on 186,746,431 shares outstanding. The notice also identifies 9,081 shares underlying Restricted Stock Units from issuer equity compensation as securities to be sold, and it lists prior sales by Cox over the past three months.

Key Figures

Shares planned for sale: 5,658 shares Aggregate market value of planned sale: $106,844.00 Shares outstanding: 186,746,431 shares +3 more

6 metrics

Shares planned for sale 5,658 shares Common stock to be sold through Stifel Nicolaus & Company Inc. under Rule 144

Aggregate market value of planned sale $106,844.00 Market value of the 5,658 shares of common stock covered by the notice

Shares outstanding 186,746,431 shares Common stock outstanding for Dyne Therapeutics, Inc. referenced in the Rule 144 notice

RSU-based shares to be sold 9,081 shares Shares underlying Restricted Stock Units from issuer equity compensation

Prior sale on June 16, 2026 2,683 shares for $49,191.00 Common stock sold by John Cox during the past three months

Prior sale on August 13, 2026 4,986 shares for $131,034.00 Common stock sold by John Cox during the past three months

Key Terms

Rule 144, Restricted Stock Units, Equity Compensation, attorney-in-fact

4 terms

Rule 144 regulatory

"See the definition of "person" in paragraph (a) of Rule 144."

Rule 144 is a U.S. securities regulation that sets conditions under which restricted or insider-held shares can be legally resold to the public, such as required holding periods, availability of public information, limits on how much can be sold at once, and certain filing requirements. For investors it matters because it determines when previously locked-up shares can enter the market — like a release valve that can increase supply, affect share price, and signal insider intent.

Restricted Stock Units financial

"Common Stock | 09/04/2026 | Restricted Stock Units | Issuer"

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.

Equity Compensation financial

"9081 | 09/04/2026 | Equity Compensation"

Equity compensation is pay given to employees, executives or contractors in the form of company ownership—such as stock, stock options or restricted shares—rather than just cash. It matters to investors because it can align workers' incentives with shareholders (like paying someone in slices of the same pie they help grow), but it also increases the number of shares outstanding and company expenses, affecting ownership percentages and earnings per share.

attorney-in-fact regulatory

"as a duly authorized representative of STIFEL, as attorney-in-fact for John Cox"

An attorney-in-fact is the person or entity given legal authority through a power of attorney to act on behalf of another for specific tasks, such as signing documents, voting shares, or handling transactions. For investors, this matters because it lets a trusted representative make timely decisions or complete paperwork when the owner cannot, much like handing keys to someone to run errands on your behalf—so checks on scope and limits of that authority are important.

FAQ

What does the Form 144 filing indicate for Dyne Therapeutics (DYN)?

The Form 144 filing indicates that an officer, John Cox, has notified of intended sales of 5,658 shares of Dyne Therapeutics common stock through broker Stifel Nicolaus & Company Inc., and identified 9,081 RSU-based shares as additional securities to be sold under Rule 144.

How many Dyne Therapeutics (DYN) shares are planned to be sold in this notice?

The notice covers a planned sale of 5,658 shares of Dyne Therapeutics common stock, with an aggregate market value of $106,844.00, as disclosed in the securities information section.

What prior sales by John Cox in Dyne Therapeutics (DYN) stock are reported?

The filing reports that John Cox sold 2,683 shares for $49,191.00 on June 16, 2026, and 4,986 shares for $131,034.00 on August 13, 2026, in Dyne Therapeutics common stock during the past three months.

What equity compensation-related securities are included for Dyne Therapeutics (DYN)?

The filing lists 9,081 shares of Dyne Therapeutics common stock underlying Restricted Stock Units, granted as equity compensation by the issuer, as securities to be sold with a date of acquisition reported as September 4, 2026.

How many Dyne Therapeutics (DYN) shares are stated as outstanding in the filing?

The Form 144 disclosure states that there are 186,746,431 shares of Dyne Therapeutics common stock outstanding, a figure used in the securities information section as part of the Rule 144 notice.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 09/08/2026 - 04:39 PM Accepted by SEC EDGAR 09/08/2026 - 04:39 PM Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001498428
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	(781) 786-8230
Name of Person for Whose Account the Securities are To Be Sold	Cox John
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	Officer

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 Stock	Stifel Nicolaus & Company Inc 501 N Broadway St. Louis MO 63102	5658	106844.00	186746431	09/08/2026	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 Stock	09/04/2026	Restricted Stock Units	Issuer			9081	09/04/2026	Equity Compensation

* 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
John Cox 1560 Trapelo Rd Waltham MA 02451	Common Stock	06/16/2026	2683	49191.00
John Cox 1560 Trapelo Rd Waltham MA 02451	Common Stock	08/13/2026	4986	131034.00

144: Remarks and Signature

Remarks
Date of Notice	09/08/2026
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	/s/ James Weimer, as a duly authorized representative of STIFEL, as attorney-in-fact for John Cox
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)