The Board of Directors, at its sole discretion, shall determine the exercise price. Stock options expire 7 to 10 years from the date of grant. The stock options generally vest 25% upon the one-year anniversary of the service inception date and then ratably each month over the remaining 36 months. Upon termination of service, any unvested stock options are automatically returned to Company. Vested stock options that are not exercised within the specified period, according to the terms and conditions of the option plan, following the termination as an

employee, consultant, or service provider to the Company are surrendered back to the Company. Those stock options are added back to the pool and made available for future grants.

The Company’s 2019 Stock Option and Grant Plan (the 2019 Plan) provided for the Company to grant stock options and other stock-based awards to employees and non-employees to purchase the Company’s common stock. Total authorized options under the 2019 Stock Option and Grant Plan is 3,464,316. Upon the effectiveness of the 2020 Plan (as defined below), no further issuances will be made under the 2019 Plan.

On July 15, 2020, the Company’s Board of Directors approved an amendment to stock options outstanding under the 2019 Stock Option and Grant Plan to provide for immediate 100% vesting for all outstanding options under the plan upon the consummation of a Sale Event, as defined by the amendment.

The 2020 Stock Option and Incentive Plan (the 2020 Plan) was approved by the Company’s board of directors on July 15, 2020, and the Company’s stockholders on July 20, 2020 and became effective on July 22, 2020, the date immediately prior to the date on which the registration statement for the Company’s IPO became effective. The 2020 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights to the Company’s officers, employees, directors and consultants. The number of shares of common stock reserved for issuance as of December 31, 2023 under the 2020 Plan was 9,115,915 and will be increased each January 1 by 5% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s compensation committee of the board of directors. Accordingly, on January 1, 2024, the number of shares of common stock reserved and available for issuance under the 2020 Plan increased by 1,791,904. The 2020 Plan replaced the 2019 Plan, as the Company’s board of directors is not expected to make additional awards under the 2019 Plan following the completion of the IPO. However, the 2019 Plan will continue to govern outstanding equity awards granted thereunder.

The 2020 Employee Stock Purchase Plan (the 2020 ESPP) was approved by the Company’s board of directors on July 15, 2020, and the Company’s stockholders on July 20, 2020, and became effective on July 22, 2020, the date immediately prior to the date on which the registration statement for the Company’s IPO was declared effective. The number of shares of common stock reserved for issuance as of December 31, 2023 under the 2020 ESPP was 612,642. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1 thereafter by the lesser of 634,969 shares of common stock, 1% of the outstanding number of shares of common stock on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s compensation committee. There was no increase to the number of shares of common stock reserved and available for issuance under the 2020 ESPP on January 1, 2024. During the year ended December 31, 2023, 37,549 shares were issued at a weighted-average price of $10.91 under the 2020 ESPP. The purchase price of the stock is equal to 85% of the lesser of the market value of such shares at either first date of the offering period or the last date of the offering period. The estimated weighted-average fair value of the issued shares was $7.19 per share. The assumptions utilized to estimate the fair value are include in the assumption table below.

The following table summarizes stock option activity for the year ended December 31, 2023:


	Stock Options
	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (In thousands)
Outstanding as of December 31, 2022		6,401,987		$	18.50		7.1
Granted		2,324,597			15.25
Exercised		(184,937	)		3.92
Forfeited		(271,427	)		24.14
Outstanding as of December 31, 2023		8,270,220		$	17.73		6.5	$	16,299
Vested and expected to vest as of December 31, 2023		8,270,220		$	17.73		6.5	$	16,299
Exercisable at December 31, 2023		4,746,431		$	16.01		5.3	$	14,859

The following table summarizes stock-based compensation expense, and also the allocation within the consolidated statements of operations and comprehensive income (loss):


	Year Ended December 31,
(in thousands)	2023		2022		2021
Research and development	$	6,619	$	4,152	$	1,906
General and administrative		20,402		17,409		11,888
Total stock-based compensation expense	$	27,021	$	21,561	$	13,794

Of the $27.0 million of stock-based compensation expense recognized during the year ended December 31, 2023, $25.8 million related to stock options, $1.0 million related to restricted stock units, and $0.2 million related to ESPP awards.The weighted-average grant-date fair value of options awarded during the years ended December 31, 2023, 2022 and 2021 was $11.60 per share, $23.94 per share and $27.46 per share, respectively. The aggregate intrinsic value of stock options exercised during the years ended December 31, 2023, 2022 and 2021 was $2.2 million, $3.2 million and $11.0 million, respectively. The aggregate grant date fair value of stock options vested during the years ended December 31, 2023, 2022 and 2021 was $28.1 million, $20.4 million and $10.7 million, respectively. As of December 31, 2023, there was a total of $46.7 million of unrecognized employee compensation costs related to non-vested stock option awards expected to be recognized over a weighted average period of 2.7 years.

The Company estimates the fair value of stock-based compensation utilizing the Black-Scholes option pricing model, which is dependent upon several variables, such as expected term, volatility, risk-free interest rate, and expected dividends. Each of these inputs is subjective and generally requires significant judgment to determine.

The following table summarizes the range of key assumptions used to determine the fair value of stock options and ESPP awards granted during:


	Year Ended December 31,
	2023			2022			2021
Stock Options:
Risk-free interest rate	3.46% - 4.73%			1.37% - 4.23%			0.42% - 1.27%
Expected term (in years)	5.5 - 6			5.5 - 6				6
Expected volatility	82% - 96%			86% - 94%			92% - 100%
Expected dividend yield	0				0	%	0%
Estimated fair value of common stock	$9.76 - $21.15			$17.50 - $46.56			$20.54 - $46.68
ESPP Awards:
Risk-free interest rate	1.63% - 5.44%				1.63	%		-
Expected term (in years)	0.5				0.5			-
Expected volatility	77% - 95%				81	%		-
Expected dividend yield		0	%		0	%		-
Estimated fair value of common stock	$15.85 - $20.92			$17.30				-

The Company issued restricted stock units in 2023, which vest over a two-year period, and in 2022, which vest over a four-year period. The following table summarizes the Company's restricted stock unit activity:


	Shares			Weighted average grant date fair value
Unvested as of December 31, 2022		10,000		$	35.86
Issued		512,000			11.55
Vested		(4,375	)		35.86
Cancelled		—			—
Unvested as of December 31, 2023		517,625		$	11.81

The restricted stock units granted in 2023 cliff vest 100% on the second anniversary of the grant date. The restricted stock units granted in 2022 cliff vested 25% on the anniversary of the grant date. The remainder of these units will vest in quarterly increments over the remaining three years of the vesting period. 4,375 restricted stock units had vested as of December 31, 2023. As of December 31, 2023, there was $5.2 million of unrecognized stock-based compensation expense related to restricted stock units that are expected to vest. These costs are expected to be recognized over a weighted-average period of 1.6 years.