IDYA · IDEAYA Biosciences, Inc.

The transaction reported herein was effected pursuant to the Reporting Person's Rule 10b5-1 trading plan, adopted on December 19, 2025.

This transaction was executed in multiple trades in prices ranging from $40.00 to $40.10, inclusive. The price reported in Column 4 above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide to the Securities and Exchange Commission staff, the Issuer, or a security holder of the Issuer, upon request, full information regarding the number of shares sold at each respective price within the range set forth in this footnote.

100% of the shares subject to the option is fully vested and exercisable.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

This transaction was executed in multiple trades in prices ranging from $32.743 to $33.1999, inclusive. The price reported in Column 4 above reflects the weighted average purchase price. The Reporting Person hereby undertakes to provide to the Securities and Exchange Commission staff, the Issuer, or a security holder of the Issuer, upon request, full information regarding the number of shares purchased at each respective price within the range set forth in this footnote.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2026 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2026 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2026 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2026 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2026 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2026 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2026 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

The shares were acquired under the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

The shares were acquired under the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

The shares were acquired under the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2025 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2025 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2025 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2025 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2025 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2025 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

The shares subject to the option are fully vested and exercisable.

The shares were acquired under the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

25% of the shares subject to the option vest on the first anniversary measured from September 18, 2024 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

25% of the shares subject to the option vest on the first anniversary measured from July 1, 2020 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.

The shares subject to the option are fully vested and exercisable.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

100% of the shares subject to the option shall vest in full on the earlier of (i) the first anniversary of the date of grant and (ii) immediately prior to the Annual Meeting following the date of grant, subject to the Reporting Person continuing in service on the Board through such vesting date.

25% of the shares subject to the option vest on the first anniversary measured from January 1, 2022 (the "Vesting Commencement Date"), and 1/48th of the total number of shares vest monthly thereafter, such that 100% of the shares subject to the option will be fully vested and exercisable on the fourth anniversary of the Vesting Commencement Date.