A Form 4 filed on August 17, 2026 reports that John Cox, CEO and President of Dyne Therapeutics, Inc. (NASDAQ:DYN), disposed of 4,986 shares of common stock on August 13, 2026 to satisfy tax withholding obligations tied to vesting restricted stock units.

Key Highlights

  • Transaction date: 4,986 shares of common stock were disposed of on August 13, 2026 via transaction code "S."
  • Weighted average price: Shares were sold at a weighted average price of $26.28, within a range of $26.17 to $26.39, inclusive.
  • Tax withholding purpose: The sale was automatically executed to satisfy tax withholding obligations connected to restricted stock units granted on February 12, 2026.
  • Rule 10b5-1 plan: According to the filing, the sale was made pursuant to a "binding contract" consistent with the affirmative defense conditions of Rule 10b5-1(c) and "does not represent a discretionary trade by the Reporting Person."
  • Direct ownership following transaction: Cox directly beneficially owned 363,165 shares after the reported transaction, including 248,314 unvested RSUs.
  • Indirect holdings: An additional 72,000 shares are held indirectly across four trusts (18,000 shares each), each for the benefit of a child of the reporting person.

Details of John Cox's August 2026 Share Disposition at Dyne Therapeutics

According to the filing, John Cox, who serves as both CEO and President and as a Director of Dyne Therapeutics, Inc., disposed of 4,986 shares of common stock on August 13, 2026. The filing indicates the transaction was an automatic sale to cover tax withholding obligations arising from the vesting of restricted stock units originally granted on February 12, 2026. The filing states the sale was provided for in a restricted stock unit agreement constituting a "binding contract" under Rule 10b5-1.

The filing reports that the shares were sold in multiple transactions at prices ranging from $26.17 to $26.39, inclusive, with a weighted average price of $26.28. The filing further notes that Cox "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."

Following the reported transaction, Cox directly beneficially owned 363,165 shares, of which 248,314 are described as unvested RSUs. In addition, the filing reports 72,000 shares held indirectly through four separate trusts (18,000 shares each), each established for the benefit of a child of Cox. The Form 4 was signed by Dan Wilson as Attorney-in-Fact and filed on August 17, 2026.

What Was Disclosed

The filing discloses an automatic tax-withholding sale of 4,986 common shares by Dyne Therapeutics CEO John Cox on August 13, 2026, at a weighted average price of $26.28 per share, executed under a Rule 10b5-1 plan tied to RSU vesting.