The Company’s Board of Directors and stockholders adopted and approved the Company’s 2021 Equity Incentive Plan (the “2021 Plan”) in May 2021. The 2021 Plan replaced the Company’s 2016 Equity Incentive Plan adopted in September 2016 (the “2016 Plan”); however, awards outstanding under the 2016 Plan will continue to be governed by their existing terms. The number of shares of the Company’s common stock that were initially available for issuance under the 2021 Plan equaled the sum of 7,500,000 shares plus 832,980 shares that were then available for issuance under the 2016 Plan. The 2021 Plan provides for the following types of awards: incentive and nonqualified stock options, stock appreciation rights, restricted shares and restricted stock units.

The number of shares of common stock reserved for issuance under the 2021 Plan are increased automatically on the first business day of each fiscal year, commencing in 2022 and ending in 2031, by a number equal to the lesser of: (i) 5% of the shares of common stock outstanding on the last business day of the prior fiscal year; or (ii) the number of shares determined by the Company’s Board of Directors. In general, to the extent that any awards under the 2021 Plan are forfeited, terminated, expired or lapsed without the issuance of shares, or if the Company reacquires the shares subject to awards granted under the 2021 Plan, those shares will again become available for issuance under the 2021 Plan, as will shares applied to pay the exercise or purchase price of an award or to satisfy tax withholding obligations related to an award.

Stock-based awards are governed by agreements between the Company and the recipients. Incentive stock options and nonqualified stock options may be granted under the 2021 Plan (and previously the 2016 Plan) at an exercise price of not less than 100% of the fair market value of the Company’s common stock on the date of grant. The grant date is the date the terms of the award are formally approved by the Company’s Board of Directors or its designee.

The following table summarizes stock option activity under the stock incentive plans since December 31, 2021:


		Number of Options			Weighted-Average Exercise Price (per Share)		Weighted-Average Remaining Contract Term (in Years)

Outstanding at December 31, 2021			5,322,314		$	6.75
Exercisable at December 31, 2021			3,296,183			3.03
	Granted		4,754,555			6.94
	Exercised		(228,043	)		0.45
	Canceled or forfeited		(514,455	)		20.42
Outstanding at June 30, 2022			9,334,371			6.80		8.84
Exercisable at June 30, 2022			3,599,146			4.12		7.76

The 2016 Plan allows for the early exercise of awards to plan participants subject to the right of repurchase by the Company at the lower of the original exercise price or fair market value for unvested awards. At June 30, 2022 and December 31, 2021, the Company has a liability for the cash received from the early exercise of stock options in the amount of $0.7 million and $1.7 million, respectively. The Company reduces the liability as the underlying shares vest in accordance with the vesting terms of the awards or when the Company repurchases unvested awards.

As of June 30, 2022 and December 31, 2021, there were 845,429 and 2,198,933, respectively, of early exercised stock options that remain subject to the Company’s repurchase right.

In May 2021, the Company’s Board of Directors approved the 2021 Employee Stock Purchase Plan (the “ESPP”). A total of 730,000 shares of common stock was initially reserved for issuance under the ESPP. The price at which common stock is purchased by employees under the ESPP is equal to 85% of the fair market value of the common stock on the first day of the offering period or purchase date, whichever is lower.

During the six months ended June 30, 2022, 174,019 shares of common stock were issued under the ESPP.

The classification of stock-based compensation expense is summarized as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	1,012	$	581	$	1,921	$	806
Selling, general and administrative		2,593		1,760		5,250		2,631
Total stock-based compensation expense	$	3,605	$	2,341	$	7,171	$	3,437

As of June 30, 2022, total unrecognized stock-based compensation expense was $33.0 million and is expected to be recognized over the weighted-average period of approximately 2.8 years.

The following table shows the weighted-average assumptions used to compute the fair value of the awards granted to employees and nonemployees using the Black-Scholes option pricing model during the periods below:


	Six Months Ended June 30,
Assumption	2022	2021
Expected volatility	57.27%	78.68%
Expected term (years)	5.3−6.1	5.5−6.1
Expected dividend yield	0.00%	0.00%
Risk-free interest rate	1.86%	0.90%
Forfeiture rate	0.00%	0.00%

Common stock reserved for future issuance consisted of the following as of June 30, 2022:


Stock options issued and outstanding under all Plans			9,334,371
Authorized for future grants under the 2021 Plan			7,261,233
Authorized for future grants under the ESPP			1,220,972
Total as of June 30, 2022			17,816,576