Dyne Therapeutics, Inc. Stock Compensation Disclosure

8. Stockholders' Equity

Common Stock

In November 2021, the Company entered into an Open Market Sale Agreement (the "Sales Agreement") with Jefferies LLC ("Jefferies") as the Company's sales agent. On March 5, 2024, the Company filed a universal shelf registration statement on Form S-3, (the “2024 Shelf Registration Statement”), and included a prospectus relating to the Sales Agreement. Under the 2024 Shelf Registration Statement, the Company may offer and sell debt securities, common stock, preferred stock, units and/or warrants from time to time at an indeterminate aggregate offering price in one or more offerings. In November 2024, the Company filed a prospectus supplement relating to the Sales Agreement, pursuant to which, in accordance with the Sales Agreement, the Company may offer and sell shares of its common stock having an aggregate offering price of up to $300.0 million in an “at-the-market” offering.



During the year ended December 31, 2025, the Company issued and sold an aggregate of 10,660,159 shares of common stock pursuant to the Sales Agreement for aggregate net proceeds of $140.6 million, after deducting commissions and offering expenses payable by the Company. The Company sold such shares at a weighted average price of $13.60 per share.

Atlas Venture and related affiliated entities were beneficial owners of approximately 5.5% of the Company's outstanding common stock as of December 31, 2025. The chairman of the Company's board of directors is a partner at Atlas Venture. On January 27, 2025, the Company issued and sold 1,111,111 shares of common stock through its at-the-market offering program that Atlas Venture and related affiliated entities purchased at a purchase price of $13.50 per share for aggregate gross proceeds of $15.0 million. The shares were purchased at the prevailing market price.

In July 2025, the Company completed a follow-on public offering, pursuant to which the Company issued

and sold 27,878,788 shares of the Company's common stock. The Company received net proceeds of $215.8 million, after deducting underwriting discounts and commissions and offering expenses paid by the Company.

In December 2025, the Company completed a follow-on public offering, pursuant to which the Company issued and sold 21,827,549 shares of the Company's common stock. The Company received net proceeds of $377.7 million, after deducting underwriting discounts and commissions and offering expenses paid by the Company.

2020 Stock Incentive Plan

In August 2020 the Company’s board of directors adopted and the Company’s stockholders approved the 2020 Stock Incentive Plan (the "2020 Plan"), which became effective on September 16, 2020. The 2020 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards to employees, directors, consultants and advisors of the Company. The 2020 Plan is administered by the Company’s board of directors or by a committee appointed by the board of directors. Upon the effectiveness of the 2020 Plan, the Company ceased granting awards under the 2018 Stock Incentive Plan. The number of shares initially reserved for issuance under the 2020 Plan was 4,884,233. The number of shares of common stock reserved for issuance under the 2020 Plan may automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021, and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the lower of (1) 5% of the shares of common stock outstanding on such date and (2) an amount determined by the Company’s board of directors. On January 1, 2026, 8,247,527 shares were added to the shares reserved for issuance under the 2020 Plan in the sixth of these annual increases.

As of December 31, 2025, 5,391,268 shares remained available for future issuance under the 2020 Plan.

2020 Employee Stock Purchase Plan

In August 2020 the Company’s board of directors adopted and the Company’s stockholders approved the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective September 16, 2020. The 2020 ESPP is administered by the Company’s board of directors or by a committee appointed by the board of directors. The 2020 ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 488,414 shares of common stock. The number of shares of common stock reserved for issuance under the 2020 ESPP may automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the lowest of (1) 1,953,656 shares of common stock, (2) 1% of the shares of common stock outstanding on such date, and (3) an amount determined by the board of directors.

As of December 31, 2025, no offering periods have commenced under the 2020 ESPP and 488,414 shares remained available for issuance.

2024 Inducement Stock Incentive Plan

In March 2024, the Company's board of directors adopted the 2024 Inducement Stock Incentive Plan (the "2024 Inducement Plan"). The 2024 Inducement Plan provides for the grant of nonstatutory stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards with respect to an aggregate of 900,000 shares of Common Stock (subject to adjustment as provided in the 2024 Inducement Plan). Awards under the 2024 Inducement Plan may only be granted to new employees who were not previously an employee or director of the Company or are commencing employment with the Company following a bona fide period of non-employment, in either case, as an inducement material to the individual’s entering into employment with the Company and in accordance with the requirements of Nasdaq Stock Market Rule 5635(c)(4). In February 2025, the Company's board of directors approved an additional 1,000,000 shares for issuance under the 2024 Inducement Plan. During the year ended December 31, 2025, the Company granted inducement equity awards to four new employees as a

material inducement to acceptance of their respective employment consisting of stock options to purchase up to an aggregate of 544,700 shares of the Company's common stock and restricted stock units with respect to an aggregate of 168,000 shares of the Company's common stock.

As of December 31, 2025, 440,447 shares remained available for future issuance under the 2024 Inducement Plan.

Stock option valuation

The fair value of stock option grants is estimated using the Black-Scholes option-pricing model for stock options with service-based vesting conditions. The fair value is determined based upon the quoted price of the Company’s common stock. The Company lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The fair value of market-based stock options is estimated using a Monte Carlo valuation method, incorporating various option pricing inputs.

Stock option activity

The intrinsic value of options exercised for the years ended December 31, 2025, 2024 and 2023 totaled $6.6 million, $90.3 million and $8.1 million, respectively. The weighted-average grant date fair value of the options granted during the years ended December 31, 2025, 2024 and 2023 was $7.24 per share, $19.22 per share and $7.28 per share, respectively. As of December 31, 2025, there was $64.9 million of

unrecognized compensation expense, which the Company expects to recognize over a weighted-average period of 2.7 years.

Effective January 2025, the Company entered into a consulting agreement with its former chief medical officer resulting in the modification of previously issued stock option awards. The modification resulted in $0.9 million of additional stock-based compensation expense, all of which was recognized during the three months ended March 31, 2025. The expense was recorded within research and development expenses on the condensed consolidated statements of operations and comprehensive loss. Based on the terms of the consulting agreement, options to purchase 58,659 shares of common stock were forfeited in January 2025.

In July 2025, the Company granted 591,685 stock options, vesting over a three-year term from the grant date and contingent upon the achievement of certain market conditions. The fair value of these market-based stock options was estimated using a Monte Carlo valuation method, incorporating various option pricing inputs. The estimated grant date fair value of $2.8 million will be recognized as expense over the three-year service period. $0.7 million was recognized as expense during the year ended December 31, 2025.



Restricted stock units

A restricted stock unit (“RSU”) represents the right to receive one share of common stock upon vesting of the RSU. The Company grants RSUs with service conditions that vest in four equal annual installments provided that the employee remains employed with the Company, RSUs with service conditions that vest in sixteen equal quarterly installments provided that the employee remains employed with the Company and RSUs with performance-based vesting conditions. As of December 31, 2025, there are no RSUs with performance-based vesting conditions outstanding. The fair value of each RSU is based on the closing price of the Company’s common stock on the date of grant. A summary of the Company’s RSU activity and related information for the year ended December 31, 2025 is as follows:

The fair value of RSUs vested during the years ended December 31, 2025, 2024 and 2023 totaled $17.6 million, $32.7 million and $5.6 million, respectively. The weighted average grant date fair value of RSUs granted during the year ended December 31, 2024 was $30.53. As of December 31, 2025, there was $45.0 million of unrecognized compensation costs related to unvested RSUs, which are expected to be recognized over a weighted-average period of 2.7 years.

Effective January 2025, the Company entered into a consulting agreement with its former chief medical officer resulting in the modification of previously issued RSU awards. The modification resulted in the recognition of $0.3 million of additional stock-based compensation expense, all of which was recognized during the three months ended March 31, 2025. The expense was recorded within research and development expenses on the condensed consolidated statements of operations and comprehensive loss. Based on the terms of the consulting agreement, 76,662 RSUs were forfeited in January 2025.