In July 2021, the Company’s board of directors adopted and the Company’s stockholders approved the Company’s 2021 Incentive Award Plan (the 2021 Plan), which became effective in connection with the IPO. Upon the adoption of the 2021 Plan, the Company ceased making equity grants under its 2018 Equity Incentive Plan (the 2018 Plan). Under the 2021 Plan, the Company may grant stock options, restricted stock, restricted stock units, stock appreciation rights, and other stock or cash-based awards to individuals who are then employees, officers, directors or non-entity consultants of the Company. A total of 15,150,000 shares of common stock were initially reserved for issuance under the 2021 Plan. In addition, the number of shares of common stock available for issuance under the 2021 Plan may be increased annually on the first day of each calendar year during the term of the 2021 Plan, beginning in 2022, by an amount equal to the lesser of (i) 5% of the shares of common stock outstanding on the final day of the immediately preceding calendar year or (ii) such smaller number of shares as determined by the Company’s board of directors or an authorized committee of the board of directors. As of March 31, 2023, there were 14,846,946 stock-based awards available for future grant under the 2021 Plan.

Subsequent to July 2021, no further awards will be granted under the 2018 Plan and all future stock-based awards will be granted under the 2021 Plan. To the extent outstanding options or restricted stock granted under the 2018 Plan are cancelled, forfeited, repurchased, or otherwise terminated without being exercised or becoming vested, and would otherwise have been returned to the share reserve under the 2018 Plan, the number of shares underlying such awards will be available for future grant under the 2021 Plan.

Options granted are exercisable at various dates as determined upon grant and will expire no more than ten years from their date of grant. Stock options generally vest over a four-year term. The exercise price of each option shall be determined by the Company’s board of directors based on the estimated fair value of the Company’s stock on the date of the option grant. The exercise price shall not be less than 100% of the fair market value of the Company’s common stock at the time the option is granted. For holders of more than 10% of the Company’s total combined voting power of all classes of stock, incentive stock options may not be granted at less than 110% of the fair market value of the Company’s common stock on the date of grant and for a term that exceeds five years. Early exercise is permitted for certain grants under the 2018 Plan.

A summary of the Company’s stock option activity under the 2021 Plan and 2018 Plan is as follows (in thousands, except share and per share data and years):


						Weighted-
				Weighted-		average remaining		Aggregate
				average		contractual		intrinsic
	Shares			exercise price		term (years)		value
Outstanding at December 31, 2022		17,393,396		$	5.84		8.20	$	18,295
Granted		9,025,337			4.00
Exercised		(199,344	)		0.92
Canceled		(327,118	)		5.48
Outstanding at March 31, 2023		25,892,271		$	5.24		8.61	$	8,752
Options exercisable at March 31, 2023		8,166,304		$	4.45		7.54	$	6,553

The weighted-average grant date fair value of options granted for the three months ended March 31, 2023 and 2022 was $2.94 and $8.36, respectively. As of March 31, 2023, the unrecognized compensation cost related to unvested stock option grants was $72.0 million and is expected to be recognized as expense over approximately 2.87 years. The intrinsic value of the options exercised for the three months ended March 31, 2023 and 2022 was $517,000 and $3.4 million, respectively.

Prior to the IPO, certain individuals were granted the ability to early exercise their stock options. The shares of common stock issued from the early exercise of unvested stock options are restricted and continue to vest in accordance with the original vesting schedule. The Company has the option to repurchase any unvested shares at the original purchase price upon any voluntary or involuntary termination. The shares purchased by the employees and non-employees pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be outstanding until those shares vest. The cash received in exchange for exercised and unvested shares related to stock options granted is recorded as a liability for the early exercise of stock options on the accompanying condensed consolidated balance sheets and will be transferred into common stock and additional paid-in capital as the shares vest. As of March 31, 2023 and December 31, 2022, there were 948,179 shares and 1,115,105 shares subject to repurchase by the Company, respectively. As of March 31, 2023 and December 31, 2022, the Company recorded $1.5 million and $1.7 million of liabilities associated with shares issued with repurchase rights, respectively, which is recorded in accrued expenses and other current liabilities.

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants were as follows:


	Three Months Ended March 31,
	2023	2022
Risk-free interest rate	3.46%-4.22%	1.46%-1.74%
Expected volatility	85.52%-85.81%	85.86%-85.99%
Expected term (in years)	6.02-6.07	5.99-6.08
Expected dividend yield	--%	--%

In July 2021, the Company’s board of directors adopted and the Company’s stockholders approved the Company's 2021 Employee Stock Purchase Plan (the ESPP), which became effective in connection with the IPO. The ESPP permits participants to contribute up to a specified percentage of their eligible compensation during a series of offering periods of 24 months, each comprised of four six-month purchase periods, to purchase the Company’s common stock. The purchase price of the shares will be 85% of the fair market value of the Company’s common stock on the first day of trading of the applicable offering period or on the applicable purchase date, whichever is lower. A total of 1,260,000 shares of common stock was initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP may be increased annually on the first day of each calendar year during the term of the ESPP, beginning in 2022, by an amount equal to the lesser of (i) 1% of the shares of common stock outstanding on the final day of the immediately preceding calendar year or (ii) such smaller number of shares as determined by the Company’s board of directors or an authorized committee of the board of directors. The Company recognized stock-based compensation expense related to the ESPP of $707,000 and $501,000 during the three months ended March 31, 2023 and 2022, respectively. As of March 31, 2023, the unrecognized compensation cost related to the ESPP was $2.2 million and is expected to be recognized as expense over approximately 1.24 years. As of March 31, 2023 and December 31, 2022, $418,000 and $74,000 has been withheld on behalf of employees for future purchase under the ESPP, respectively, and is included in accrued expenses and other current liabilities on the condensed consolidated balance sheets. No shares were issued and sold under the ESPP during the three months ended March 31, 2023 and 2022.

The allocation of stock-based compensation for all stock awards was as follows (in thousands):


	Three Months Ended March 31,
	2023		2022
Research and development	$	3,880	$	2,732
General and administrative		2,965		1,710
Total	$	6,845	$	4,442

Common stock reserved for future issuance consisted of the following as of March 31, 2023 and December 31, 2022:


	March 31,		December 31,
	2023		2022
Stock options issued and outstanding		25,892,271		17,393,396
Awards available for future grant		14,846,946		16,022,747
Shares available for purchase under the ESPP		2,469,614		965,131
Total		43,208,831		34,381,274