Material Event (Form 8-K)

On May 5, 2026, IDEAYA Biosciences, Inc. (the "Company") filed with the Securities and Exchange Commission (the "SEC") an automatic shelf registration statement on Form S-3ASR (Registration No. 333-295560) (the "New Registration Statement") to replace its existing automatic shelf registration statement on Form S-3 (Registration No. 333-272936) filed with the SEC on June 26, 2023 (the "Prior Registration Statement"), which was scheduled to expire on June 26, 2026 pursuant to Rule 415(a)(5) under the Securities Act of 1933, as amended (the "Securities Act"). Pursuant to Rule 415(a)(6) under the Securities Act, the Prior Registration Statement was deemed terminated as of the effective date of the New Registration Statement on May 5, 2026.

In connection with the filing of the New Registration Statement, on May 5, 2026, the Company filed with the SEC a prospectus supplement, dated May 5, 2026, to the New Registration Statement (the "ATM Prospectus Supplement") pursuant to the Open Market Sales Agreement (the "Sales Agreement"), dated as of January 19, 2024, with Jefferies LLC ("Jefferies"), under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock, par value $0.0001 per share (the "Common Stock"), having aggregate gross proceeds of up to $156.6 million, representing the remaining capacity available under the Sales Agreement, through Jefferies as its sales agent.

Prior to the termination of the Prior Registration Statement, the Company had offered and sold shares of its common stock having an aggregate gross sales price of $193,447,003.19 under the Sales Agreement and, therefore, shares of common stock having an aggregate offering price of up to $156,552,996.81 remain available for offer and sale pursuant to the Sales Agreement and the New Registration Statement.

Latham & Watkins LLP, counsel to the Company, has issued an opinion to the Company, dated May 5, 2026, relating to the validity of the shares of the Company's common stock that may be offered and sold pursuant to the ATM Prospectus Supplement, a copy of which is filed as Exhibit 5.1 to this Current Report.

This Current Report shall not constitute an offer to sell or the solicitation of an offer to buy any shares of Common Stock, nor shall there be any offer, solicitation or sale of such shares of Common Stock in any state or country in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or country.