Brian S. Posner

CIK: 0001372455

Transaction Breakdown

Open Market Buys (P)9 (56.3%)

High conviction signal

Open Market Sales (S)3 (18.8%)

Position reduction

Option Exercises (M)0 (0.0%)

Derivative conversions

Awards (A)4 (25.0%)

Compensation grants

Other (G, F, J, C, D, …)0 (0.0%)

Gifts, tax withholding, conversions, dispositions to the issuer and other codes

Companies & Roles (2)

DYN

Dyne Therapeutics, Inc.

Director

ACGL

ARCH CAPITAL GROUP LTD.

Director

Discretionary Trading P&L

Holdings

Transaction History (16 total)

DYN
Dyne Therapeutics, Inc.
Oct 2, 2026
Purchase(P)
Direct
2.5K shares at avg. $16.00$40K
DYN
Dyne Therapeutics, Inc.
Jun 8, 2026
Purchase(P)
Direct
2K shares at avg. $16.94$34K
DYN
Dyne Therapeutics, Inc.
Jun 5, 2026
Award(A)
Stock option (right to buy)
Direct
35.2K shares-
DYN
Dyne Therapeutics, Inc.
Jun 3, 2026
Purchase(P)
Direct
2.5K shares at avg. $17.48$44K
ACGL
ARCH CAPITAL GROUP LTD.
Jun 3, 2026
Sale(S)
Direct
3K shares at avg. $19.66$59K
DYN
Dyne Therapeutics, Inc.
May 26, 2026
Purchase(P)
Direct
2K shares at avg. $18.21$36K
DYN
Dyne Therapeutics, Inc.
May 20, 2026
Purchase(P)
Direct
2.5K shares at avg. $17.12$43K
ACGL
ARCH CAPITAL GROUP LTD.
May 11, 2026
Sale(S)
Direct
2K shares at avg. $17.14$34K
ACGL
ARCH CAPITAL GROUP LTD.
May 5, 2026
Award(A)
Direct
2.1K shares-
DYN
Dyne Therapeutics, Inc.
Mar 30, 2026
Purchase(P)
Direct
2K shares at avg. $17.08$34K
DYN
Dyne Therapeutics, Inc.
Mar 11, 2026
Purchase(P)
Direct
2K shares at avg. $19.35$39K
ACGL
ARCH CAPITAL GROUP LTD.
Mar 11, 2026
Sale(S)
Direct
3K shares at avg. $17.11$51K
DYN
Dyne Therapeutics, Inc.
Mar 6, 2026
Purchase(P)
Direct
3K shares at avg. $15.06$45K
DYN
Dyne Therapeutics, Inc.
Oct 1, 2025
Award(A)
Stock option (right to buy)
Direct
70K shares-
ACGL
ARCH CAPITAL GROUP LTD.
Aug 1, 2025
Purchase(P)
Direct
1K shares at avg. $17.34$17K
ACGL
ARCH CAPITAL GROUP LTD.
May 7, 2025
Award(A)
Direct
1.6K shares-

		Type	Shares	Price		Ownership
Oct 2, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	2,500	$16.00	$40,000	Direct
Jun 8, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	2,000	$16.94	$33,880	Direct
Jun 5, 2026	DYN Dyne Therapeutics, Inc.	Award(A) Stock option (right to buy)	35,152	-	-	Direct
Jun 3, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	2,500	$17.48	$43,700	Direct
Jun 3, 2026	ACGL ARCH CAPITAL GROUP LTD.	Sale(S)	3,000	$19.66	$58,980	Direct
May 26, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	2,000	$18.21	$36,420	Direct
May 20, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	2,500	$17.12	$42,800	Direct
May 11, 2026	ACGL ARCH CAPITAL GROUP LTD.	Sale(S)	2,000	$17.14	$34,283	Direct
May 5, 2026	ACGL ARCH CAPITAL GROUP LTD.	Award(A)	2,071	-	$0	Direct
Mar 30, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	2,000	$17.08	$34,160	Direct
Mar 11, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	2,000	$19.35	$38,700	Direct
Mar 11, 2026	ACGL ARCH CAPITAL GROUP LTD.	Sale(S)	3,000	$17.11	$51,345	Direct
Mar 6, 2026	DYN Dyne Therapeutics, Inc.	Purchase(P)	3,000	$15.06	$45,180	Direct
Oct 1, 2025	DYN Dyne Therapeutics, Inc.	Award(A) Stock option (right to buy)	70,000	-	-	Direct
Aug 1, 2025	ACGL ARCH CAPITAL GROUP LTD.	Purchase(P)	1,000	$17.34	$17,338	Direct
May 7, 2025	ACGL ARCH CAPITAL GROUP LTD.	Award(A)	1,564	-	-	Direct

1-16 of 16 transactions

About Posner Brian S

Posner Brian S (SEC CIK 0001372455) files insider reports with the SEC as Director of Dyne Therapeutics, Inc. (DYN) and Director of ARCH CAPITAL GROUP LTD. (ACGL).

Signal8 holds 16 ownership filings by Posner Brian S (1 Form 3, 15 Form 4), filed between May 9, 2025 and Oct 6, 2026. Those filings report 16 transactions, from May 7, 2025 to Oct 2, 2026. Signal8's Form 4 history starts in Sep 2024.

The business address on Posner Brian S's filings is in WALTHAM, MA.

Recent filings by Posner Brian S

Oct 2, 2026: Open-market purchase of DYN shares (Form 4, code P).
Jun 8, 2026: Open-market purchase of DYN shares (Form 4, code P).
Jun 5, 2026: Grant or award of DYN derivative securities (Form 4, code A).
Jun 3, 2026: Open-market purchase of DYN shares (Form 4, code P).
Jun 3, 2026: Open-market sale of ACGL shares (Form 4, code S).

Other insiders filing for Dyne Therapeutics, Inc. (DYN)

Kerr Douglas, Head of R&D and CMO
Friedl-Naderer Johanna, Chief Commercial Officer
Cox John, CEO & President
Rhodes Jason P, Director
Lucera Erick, Chief Financial Officer
Kersten Dirk, Director

How to read Form 4 transaction codes