SNDX · Syndax Pharmaceuticals Inc

This option is fully vested.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person. Following the sales reported in this Form 4, the Reporting Person has a total of 1,564,551 options to purchase shares of common stock that are vested and immediately exercisable and a total of 813,949 options to purchase shares of common stock that have not yet vested.

The sale prices ranged from $24.00 to $24.43

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person. Following the sales reported in this Form 4, the Reporting Person has a total of 16,537 options to purchase shares of common stock that are vested and immediately exercisable and a total of 289,413 options to purchase shares of common stock that have not yet vested.

These transactions were executed in multiple trades at prices ranging from $18.00 to $18.32. The price reported above reflects the weighted-average sale price of all transactions executed on that date.

The shares sold in this transaction were fully vested.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person. Following the sales reported in this Form 4, the Reporting Person has a total of 16,537 options to purchase shares of common stock that are vested and immediately exercisable and a total of 289,413 options to purchase shares of common stock that have not yet vested.

These transactions were executed in multiple trades at prices ranging from $17.31 to $18.10. The price reported above reflects the weighted-average sale price of all transactions executed on that date.

The shares sold in this transaction were fully vested.

Represents the number of shares required to be sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.

Represents the number of shares required to be sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.

Represents the number of shares required to be sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.

Represents the number of shares required to be sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.

Represents the number of shares required to be sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.

Represents the number of shares required to be sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.

1/48th of the shares subject to the option shall vest monthly over a four-year period.

Award of Restricted Stock Units that vests one year from the date of grant. The shares underlying such Restricted Stock Units will not be delivered to the Reporting Person and may not be transferred or sold until the earlier of a separation from service, death, disability or change in control.

Award of Restricted Stock Units that vests one year from the date of grant. The shares underlying such Restricted Stock Units will not be delivered to the Reporting Person and may not be transferred or sold until the earlier of a separation from service, death, disability or change in control.

Award of RSUs, representing the right to receive one share of Common Stock for each RSU. The number of shares of Common Stock acquired upon vesting of the RSUs is contingent upon the achievement of pre-established performance metrics, as approved by the Company's Compensation Committee, subject to the Reporting Person's continued service as an employee, consultant, director or officer of the Company.

Award of Restricted Stock Units that vests one year from the date of grant. The shares underlying such Restricted Stock Units will not be delivered to the Reporting Person and may not be transferred or sold until the earlier of a separation from service, death, disability or change in control.

1/48th of the shares subject to the option shall vest monthly over a four-year period.

Award of restricted stock units ("RSUs"), representing the right to receive one share of Common Stock for each RSU. One third (1/3rd) of the shares of Common Stock subject to such RSU shall vest annually on the anniversary of the Vesting Commencement Date, during the Reporting Person's continued service as an employee, consultant, director or officer of the Company over the three (3) years following the date of grant, until all of the shares subject to such RSU are fully vested.

Award of restricted stock units ("RSUs"), representing the right to receive one share of Common Stock for each RSU. One third (1/3rd) of the shares of Common Stock subject to such RSU shall vest annually on the anniversary of the Vesting Commencement Date, during the Reporting Person's continued service as an employee, consultant, director or officer of the Company over the three (3) years following the date of grant, until all of the shares subject to such RSU are fully vested.

Award of Restricted Stock Units that vests one year from the date of grant. The shares underlying such Restricted Stock Units will not be delivered to the Reporting Person and may not be transferred or sold until the earlier of a separation from service, death, disability or change in control.

1/48th of the shares subject to the option shall vest monthly over a four-year period.

Award of Restricted Stock Units that vests one year from the date of grant. The shares underlying such Restricted Stock Units will not be delivered to the Reporting Person and may not be transferred or sold until the earlier of a separation from service, death, disability or change in control.

Award of Restricted Stock Units that vests one year from the date of grant. The shares underlying such Restricted Stock Units will not be delivered to the Reporting Person and may not be transferred or sold until the earlier of a separation from service, death, disability or change in control.

Award of RSUs, representing the right to receive one share of Common Stock for each RSU. The number of shares of Common Stock acquired upon vesting of the RSUs is contingent upon the achievement of pre-established performance metrics, as approved by the Company's Compensation Committee, subject to the Reporting Person's continued service as an employee, consultant, director or officer of the Company.

Award of restricted stock units ("RSUs"), representing the right to receive one share of Common Stock for each RSU. One third (1/3rd) of the shares of Common Stock subject to such RSU shall vest annually on the anniversary of the Vesting Commencement Date, during the Reporting Person's continued service as an employee, consultant, director or officer of the Company over the three (3) years following the date of grant, until all of the shares subject to such RSU are fully vested.

Award of RSUs, representing the right to receive one share of Common Stock for each RSU. The number of shares of Common Stock acquired upon vesting of the RSUs is contingent upon the achievement of pre-established performance metrics, as approved by the Company's Compensation Committee, subject to the Reporting Person's continued service as an employee, consultant, director or officer of the Company.

The Reporting Person is voluntarily filing this Form 4 to report the acquisition of 1,219 shares by the Reporting Person on 1/30/2026 pursuant to the Issuer's Employee Stock Purchase Plan.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person solely covering equity grants with expiration dates prior to September 10, 2025. Following the sales reported in this Form 4, the Reporting Person has a total of 1,319,634 options to purchase shares of common stock that are vested and immediately exercisable and a total of 651,241 options to purchase shares of common stock that have not yet vested.

The sale prices ranged from $16.21 to $17.06.

This option is fully vested.

This option is fully vested.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person solely covering equity grants with expiration dates prior to August 21, 2025. Following the sales reported in this Form 4, the Reporting Person has a total of 135,000 options to purchase shares of common stock that are vested and immediately exercisable and no unvested options to purchase shares of common stock.

The sale prices ranged from $15.61 to $16.00.

This option is fully vested.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person solely covering equity grants with expiration dates prior to August 21, 2025. Following the sales reported in this Form 4, the Reporting Person has a total of 135,000 options to purchase shares of common stock that are vested and immediately exercisable and no unvested options to purchase shares of common stock.

The sale prices ranged from $14.88 to $15.91.

This option is fully vested.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person solely covering equity grants with expiration dates prior to August 21, 2025. Following the sales reported in this Form 4, the Reporting Person has a total of 135,000 options to purchase shares of common stock that are vested and immediately exercisable and no unvested options to purchase shares of common stock.

The sale prices ranged from $13.30 to $14.80.

This option is fully vested.

The Reporting Person is voluntarily filing this Form 4 to report the acquisition of 1,226 shares by the Reporting Person on 07/31/2025 pursuant to the Issuer's Employee Stock Purchase Plan.

Represents the number of shares sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.

Represents the number of shares sold by the reporting person to cover tax withholding obligations in connection with the vesting of restricted stock units.