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 220,251 and 2,213,773 shares of Class A common stock for future 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 September 30, 2021, there were 1,510,665 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)
Balance – December 31, 2020		1,855,507		$	2.99		9.79	$	8
Granted		1,188,064			8.98
Exercised		(145,805	)		3.77
Cancelled and forfeited		(3,095	)		9.38
Balance – September 30, 2021		2,894,671			5.43		9.35	$	34,521
Options exercisable – September 30, 2021		82,944			3.42		8.96	$	1,155
Vested and expected to vest –September 30, 2021		2,894,671		$	5.43		9.35	$	34,521

The aggregate intrinsic value of stock options exercised during the three and nine months ended September 30, 2021, was zero and $206, respectively. The weighted-average grant date fair value of options granted during the three and nine months ended September 30, 2021, was $9.94 and $6.66, respectively, per share.

The ESPP enables eligible employees to purchase shares of the Company's 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 September 30, 2021, no 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 three and nine months ended September 30, 2021.

The following tables summarize the stock-based compensation expense for stock options and restricted stock awards granted to employees and nonemployees that was recorded in the Company’s statements of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020.


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development	$	313	$	—	$	606	$	4
General and administrative		620		55		1,444		184
Total stock-based compensation expense	$	933	$	55	$	2,050	$	188


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Employees	$	776	$	53	$	1,878	$	182
Nonemployees		157		2		172		6
Total stock-based compensation expense	$	933	$	55	$	2,050	$	188

As of September 30, 2021, the Company had $10,348 of unrecognized stock-based compensation expense related to unvested stock options and restricted stock awards, which is expected to be recognized over a weighted-average period of approximately 3.15 years.

The fair value of stock options granted during the three and nine months ended September 30, 2021 and 2020 was estimated using the Black-Scholes option pricing model based on the following weighted average assumptions. There were no stock options granted during the three months ended September 30, 2020.


	Three Months Ended September 30,	Nine Months Ended September 30,
	2021	2021	2020
Expected term (in years)	6.1	5.5 – 6.1	5.5 – 6.1
Expected volatility	75.4% – 75.8%	75.4% – 76.6%	74.0% – 75.7%
Risk-free rate	0.9% – 1.0%	0.6% – 1.1%	0.4% – 1.7%
Dividend yield	—	—	—

In October 2020, in conjunction with the Series C redeemable convertible preferred stock issuance, 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 allows the Company to repurchase shares that have not vested. The vesting term of restricted stock is one year. The grant date fair value of the restricted shares was $6.37.

For the nine months ended September 30, 2021, the Company recognized $236 of stock-based compensation expense related to restricted stock awards that vested during the period.