In April 2021, the Company adopted the 2021 Employee Stock Purchase Plan (ESPP) and the 2021 Equity Incentive Plan (2021 EIP), each of which became effective in connection with the IPO. The Company has reserved 429,934 and 3,260,753 shares of Class A common stock for issuance under the ESPP and 2021 EIP, respectively.

The Company may not grant any additional awards under the 2017 Equity Incentive Plan (2017 EIP). The 2017 EIP will continue to govern outstanding equity awards granted thereunder. As of December 31, 2022, there were 945,108 shares available for issuance under the 2021 EIP.

Stock option activity under the 2017 EIP and 2021 EIP was as follows:


	NUMBER OF OPTIONS			WEIGHTED- AVERAGE EXERCISE PRICE PER SHARE		WEIGHTED- AVERAGE REMAINING CONTRACTUAL LIFE (YEARS)		AGGREGATE INTRINSIC VALUE (000s)
Outstanding as of December 31, 2021		2,924,521		$	5.62		9.11	$	61,712
Granted		1,319,802			18.98
Exercised		(405,140	)		4.42
Cancelled and forfeited		(17,396	)		17.52
Outstanding as of December 31, 2022		3,821,787			10.30		8.51		35,872
Options exercisable as of December 31, 2022		1,150,982			7.07		8.17		14,363
Vested and expected to vest as of December 31, 2022		3,821,787			10.30		8.51		35,872

The aggregate intrinsic value of stock options exercised during the year ended December 31, 2022 was $5.8 million. The weighted-average grant date fair value of options granted during the year ended twelve months ended December 31, 2022 and 2021, was $13.63 per share and $9.36 per share, respectively.

The ESPP enables eligible employees to purchase shares of the Company’s Class A common stock at the end of each offering period at a price equal to 85% of the fair market value of the shares on the first trading day or the last trading day of the offering period, whichever is lower. Eligible employees generally include all employees. Share purchases are funded through payroll deductions of at least 1% and up to 15% of an employee’s eligible compensation for each payroll period. The number of shares reserved for issuance under the ESPP increase automatically on the first day of each fiscal year, beginning on January 1, 2022, by a number equal to the lesser of 440,502 shares, 1% of the total number of shares of the Company’s capital stock (including all classes of the Company’s common stock) outstanding on the last day of the calendar month prior to the date of the increase, or such lower number of shares (including no shares) approved by the Company’s board of directors. As of December 31, 2022, 15,328 shares have been issued pursuant to the ESPP. The ESPP generally provides for six-month consecutive offering periods beginning on September 14, 2021. The ESPP is a compensatory plan as defined by the authoritative guidance for stock compensation. As such, stock-based compensation expense has been recorded for the twelve months ended December 31, 2022.

The following tables summarize the stock-based compensation expense for stock options, restricted stock awards, and restricted stock units granted to employees and nonemployees and for ESPP stock-based compensation that was recorded in the Company’s statements of operations and comprehensive loss for the twelve months ended December 31, 2022 and 2021 (in thousands).


	Year Ended December 31,
	2022		2021
Research and development	$	4,592	$	915
General and administrative		4,295		2,097
Total stock-based compensation expense	$	8,887	$	3,012


	Year Ended December 31,
	2022		2021
Employees	$	5,975	$	2,605
Nonemployees		2,912		407
Total stock-based compensation expense	$	8,887	$	3,012

As of December 31, 2022, the Company had $20.3 million of unrecognized stock-based compensation expense related to unvested stock options, which is expected to be recognized over a weighted-average period of approximately 2.5 years.

The fair value of stock options granted during the year ended December 31, 2022 and 2021 was estimated using the Black-Scholes option pricing model based on the following weighted average assumptions.


	Year Ended December 31,
	2022	2021
Expected term (in years)	5.5 – 6.1	5.5 – 6.1
Expected volatility	75.8% – 77.6%	75.4% – 76.8%
Risk-free rate	1.76% – 4.2%	0.6% – 1.3%
Dividend yield	—	—

The Company grants restricted stock units (RSU) pursuant to the 2021 EIP and satisfies such grants through the issuance of the Company’s Class A common stock. The following table shows RSU activity for the period ending December 31, 2022.


	NUMBER OF SHARES			WEIGHTED- AVERAGE GRANT DATE FAIR VALUE PER SHARE
Unvested balance at December 31, 2021		77,719		$	23.99
Granted		215,750			18.38
Vested		(77,719	)		23.99
Cancelled and forfeited		(11,750	)		18.60
Unvested balance at December 31, 2022		204,000			18.37

For the twelve months ended December 31, 2022, the Company recognized $2.3 million of stock-based compensation for RSUs.

As of December 31, 2022, the Company had $3.3 million of unrecognized stock-based compensation expense related to unvested RSUs, which is expected to be recognized over a weighted-average period of approximately 1.77 years.

In October 2020, in conjunction with the Company’s issuance of Series C redeemable convertible preferred stock (which subsequently converted into Class A and Class B common stock), the Company restricted 49,636 shares of fully issued and outstanding Class A common stock held by the Company’s Chief Executive Officer and founder. The restriction allowed the Company to repurchase shares that had not vested. The vesting term of restricted stock was one year. These restricted stock awards fully vested in October 2021. The grant date fair value of the restricted stock was $6.37 per share.

No stock-based compensation expense related to restricted stock awards was recognized in 2022.