On February 24, 2023, the Company adopted the IDEAYA Biosciences, Inc. 2023 Employment Inducement Award Plan (the “2023 Inducement Plan”), pursuant to which the Company reserved 1,000,000 shares of its common stock to be used

exclusively for grants of awards to individuals who were not previously employees or directors of the Company as an inducement material to the individual’s entry into employment with the Company within the meaning of Rule 5635(c)(4) of the Nasdaq Listing Rules. The 2023 Inducement Plan was approved by the Company’s board of directors without stockholder approval in accordance with such rule. Options granted under the 2023 Inducement Plan have a term of 10 years and generally vest over a 4-year period with 1-year cliff vesting.

As of December 31, 2023, the number of shares available for issuance under the 2023 Inducement Plan was 524,300.

In May 2019, the Company’s board of directors adopted and the Company’s stockholders approved the 2019 Incentive Award Plan (the “2019 Plan”), under which the Company may grant cash and equity-based incentive awards to the Company’s employees, consultants and directors. Following the effectiveness of the 2019 Plan, the Company will not make any further grants under the 2015 Equity Incentive Plan (the “2015 Plan”). However, the 2015 Plan continues to govern the terms and conditions of the outstanding awards granted under it. Shares of common stock subject to awards granted under the 2015 Plan that are forfeited or lapse unexercised and which following the effective date of the 2019 Plan are not issued under the 2015 Plan will be available for issuance under the 2019 Plan.

Options granted under the 2019 Plan may be either incentive stock options (“ISOs”) or nonqualified stock options (“NSOs”). ISOs may be granted only to Company employees (including officers and directors who are also employees). NSOs may be granted to Company employees and consultants.

The 2019 Plan is subject to an annual increase on the first day of each year beginning in 2020 and ending in 2029, equal to the lesser of 4% of the shares outstanding on the last day of the immediately preceding fiscal year, and such small number of shares as determined by the Company's board of directors. Options granted under the 2019 Plan have a term of 10 years (or five years if granted to a 10% stockholder) and generally vest over a 4-year period with 1-year cliff vesting.

As of December 31, 2023, the number of shares available for issuance under the 2019 Plan was 964,622.

In 2015, the Company established its 2015 Plan which provides for the granting of stock options to employees and consultants of the Company. Options granted under the 2015 Plan may be either ISOs or NSOs.

In May 2019, the Company’s board of directors adopted and the Company’s stockholders approved the 2019 Employee Stock Purchase Plan (the “ESPP”). The ESPP provides eligible employees with the opportunity to acquire an ownership interest in the Company through periodic payroll deductions up to 15% of eligible compensation. The offering period is determined by the Company in its discretion but may not exceed 27 months. The per-share purchase price on the applicable exercise date for an offering period is equal to the lesser of 85% of the fair market value of the common stock at either the first business day or last business day of the offering period, provided that no more than 4,000 shares of common stock may be purchased by any one employee during each offering period.

The ESPP is intended to constitute an “employee stock purchase plan” under Section 423(b) of the Internal Revenue Code of 1986, as amended. A total of 195,000 shares of common stock were initially reserved for issuance under the ESPP, subject to an annual increase on January 1 of each year, beginning on January 1, 2020, equal to the lesser of 1% of the shares outstanding on the last day of the immediately preceding fiscal year and such number of shares as may be determined by the Company's board of directors, provided, however, that no more than 2,500,000 shares may be issued under the ESPP.

As of December 31, 2023, the number of shares available for issuance under the ESPP was 1,317,974. For the years ended December 31, 2023 and December 31, 2022, the Company recorded $0.6 million and $0.4 million, respectively, of compensation expense related to employee participation in the ESPP.

Total stock-based compensation expense recorded related to awards granted to employees and non-employees was as follows (in thousands):


	Year Ended December 31,
	2023		2022		2021
Research and development	$	10,826	$	6,050	$	3,492
General and administrative		7,663		5,579		4,745
Total stock-based compensation expense	$	18,489	$	11,629	$	8,237

Activity under the Company’s 2015 and 2019 Plans and 2023 Inducement Plan is set forth below:


	Outstanding Options
	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Balance, January 1, 2023		5,097,263		$	12.93		7.84	$	29.58
Options granted		2,694,871		$	18.95
Options exercised		(931,012	)	$	10.27
Options canceled		(591,147	)	$	16.93
Balance, December 31, 2023		6,269,975		$	15.53		7.82	$	128.49
Exercisable as of December 31, 2023		2,612,605		$	12.21		6.39	$	62.22
Vested and expected to vest as of December 31, 2023		6,269,975		$	15.53		7.82	$	128.49

The weighted-average grant-date fair value of options granted during the years ended December 31, 2023 and December 31, 2022 was $13.98 and $10.10 per share, respectively. The aggregate intrinsic value of options exercised for the years ended December 31, 2023 and December 31, 2022 was $16.9 million and $1.8 million, respectively. Intrinsic values are calculated as the difference between the exercise price of the underlying options and the fair value of the common stock on the date of exercise.

As of December 31, 2023 and December 31, 2022, the total unrecognized stock-based compensation expense for stock options was $41.1 million and $28.0 million, respectively, which is expected to be recognized over a weighted-average period of 2.59 years and 2.65 years, respectively.

The fair values of options were calculated using the assumptions set forth below:


	Year Ended December 31,
	2023	2022	2021
Expected term	6.1 years	6.1 years	5.5 - 6.1 years
Expected volatility	81.76% - 86.90%	86.76% - 89.88%	90.0% - 103.6%
Risk-free interest rate	3.56% - 4.83%	1.62% - 4.05%	0.6% - 1.4%
Dividend yield	0%	0%	0%

Expected term. The expected term represents the weighted-average period the stock options are expected to remain outstanding and is based on the options’ vesting terms, contractual terms and industry peers, as the Company does not have sufficient historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior.

Expected Volatility. The expected volatility is based on the Company's historical stock price volatility. The historical stock price volatility is calculated based on a period of time commensurate with the expected term assumption for each grant.

Risk-Free Interest Rate. The risk-free rate assumption is based on U.S. Treasury instruments whose term was consistent with the expected term of the Company’s stock options.

Expected Dividend Rate. The Company has not paid and does not anticipate paying any dividends in the near future. Accordingly, the Company has estimated the dividend yield to be zero.

The fair value of the Company’s common stock is determined based on its market price on the date of grant.