Stock Incentive Plan—In January 2022, the Company’s board of directors adopted, and its stockholders approved the 2022 Stock Option and Incentive Plan, or 2022 Plan, which became effective on January 5, 2022, at which point no further grants would be made under the 2015 Stock Option and Restricted Stock Plan, or 2015 Plan. Under the 2022 Plan, the Company may grant incentive stock options, or ISOs, non-statutory stock options, stock appreciation rights, restricted stock units, restricted stock awards and other stock-based awards. As of December 31, 2022, there were 2,817,751 shares available for future issuance under the 2022 Plan. The options issued under the 2022 Plan expire 10 years following the date of grant. Stock options and restricted stock units typically vest over 4 years. We recognize the compensation cost of awards subject to service-based vesting conditions over the requisite service period, which is generally equal to the vesting period of the respective award.

Initially, subject to adjustment as provided in the 2022 Plan, the aggregate number of shares of the Company’s common stock available for issuance under the 2022 Plan is 7,650,000. The number of shares of the Company’s common stock reserved for issuance under the 2022 Plan will automatically increase on January 1 of each year commencing January 1, 2023, by 5% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors. The maximum current number of shares that may be issued pursuant to the exercise of ISOs under the 2022 Plan is 7,650,000.

The maximum number of shares of the Company’s common stock subject to awards granted under the 2022 Plan or otherwise during a single calendar year to any individual nonemployee director, taken together with any cash fees paid by the Company to such nonemployee director during the calendar year for serving on the Company’s board of directors, will not exceed $750,000 in total value, or, with respect to the calendar year in which a nonemployee director is first appointed or elected to the Company’s board of directors, $1,000,000.

All options and awards granted under the 2015 Plan consisted of the Company’s common stock. As of January 6, 2022, no additional stock awards have been or will be granted under the 2015 Plan. Although the 2015 Plan was terminated as to future awards in January 2022, it continues to govern the terms of options that remain outstanding under the 2015 Plan.

The Company estimates the fair value of stock option awards on the grant date using the Black-Scholes option pricing model with the following weighted-average assumptions:


	Year Ended December 31,
	2022			2021
Grant price	$	20.29		$	7.69
Risk-free interest rate		1.97	%		1.01	%
Expected term (in years)		6.07			5.73
Expected volatility		88.75	%		81.61	%
Dividend yield		0.00	%		0.00	%

The per share weighted average grant date fair value of stock options granted during the year ended December 31, 2022 and 2021 was $15.10 and $5.25, respectively.

A summary of option activity for the year ended December 31, 2022, is as follows:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2021		5,339,011		$	5.54		8.7	$	15,627
Granted		4,237,720		$	20.29
Exercised		(950,013	)	$	2.33
Cancelled or forfeited		(145,768	)	$	10.98
Outstanding at December 31, 2022		8,480,950		$	13.19		8.2	$	201,765
Exercisable at December 31, 2022		2,055,416		$	6.03		7.0	$	63,408
Unvested at December 31, 2022		6,425,534		$	15.47		8.6	$	138,357

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of options exercised during the years ended December 31, 2022 and 2021, was $14.2 million and $6.2 million, respectively.

The total fair value of stock options vested during the years ended December 31, 2022 and 2021 was $8.8 million and $1.3 million, respectively.

A summary of restricted stock unit activity for the year ended December 31, 2022, is as follows:


	Number of shares			Weighted Average Grant Date Fair Value
Nonvested as of December 31, 2021		—		$	—
Granted		752,613		$	19.98
Vested		—		$	—
Forfeited		(12,316	)	$	17.82
Nonvested as of December 31, 2022		740,297		$	20.02

Stock-Based Compensation Expense—The Company recorded stock-based compensation expense in the following expense categories of its statements of operations:


	Year Ended December 31,
	2022		2021
	(in thousands)
Research and development expenses	$	5,639	$	888
Selling, general and administrative expenses		16,075		2,248
Total stock-based compensation	$	21,714	$	3,136

The following table summarizes stock-based compensation by type of award:


	Year Ended December 31,
	2022		2021
	(in thousands)
Stock options	$	18,844	$	3,136
Restricted stock units		2,870		—
Total stock-based compensation expense	$	21,714	$	3,136

The following table summarizes unrecognized stock-based compensation expense as of December 31, 2022, by type of awards, and the weighted-average period over which that expense is expected to be recognized. The total unrecognized stock-based compensation expense will be adjusted for actual forfeitures as they occur.


	As of December 31, 2022
	Unrecognized Expense		Weighted-average Recognition Period
	(in thousands)		(in years)
Stock options	$	61,049		2.79
Restricted stock units	$	11,950		3.25