The Company maintains three equity compensation plans; the 2020 Stock Plan, or the 2020 Plan, the 2022 Stock Option Incentive Plan, or the 2022 Plan, and the 2022 Employee Stock Purchase Plan, or the ESPP. As of the Company's IPO in May 2022, the Company's board of directors determined that no further awards would be made from the 2020 plan. The number of shares of common stock that may be issued under the 2022 Plan is subject to increase by the number of shares under any outstanding stock options forfeited and not exercised under the 2020 Plan. Additionally, the number of shares reserved for issuance under the 2022 Plan automatically increases on the first day of each fiscal year in an amount equal to the lower of (1) 5% of the shares of common stock outstanding on such date and (2) an amount determined by the Company’s board of directors. The 2022 Plan allows the board of directors to grant incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, unrestricted stock awards, cash-based awards, and dividend equivalent rights to the Company’s officers, employees, directors and other key persons. As of December 31, 2023, 1,091,187 shares remained available for grant under the 2022 Plan and 216,306 shares remained available for grant under the ESPP.

In determining the fair value of the stock options granted, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment.

Expected Term—The Company’s expected term represents the period that the Company’s stock-based awards are expected to be outstanding. For stock options with service-based vesting periods, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options.

Expected Volatility—The Company has historically been a private company and lacks significant company-specific historical and implied volatility information. The expected volatility is estimated based the average historical volatilities for comparable publicly traded biotechnology companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on their similar size, stage in the life cycle and area of specialty. The Company will continue to apply this process until enough historical information regarding the volatility of its own stock price becomes available.

Risk-Free Interest Rate—The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of option.

Expected Dividend Yield—The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

The fair value of stock options was estimated using the following weighted average assumptions:


	Year Ended December 31,
	2023			2022
Risk-free interest rate %		4.19	%		2.95	%
Expected volatility %		65.13	%		71.68	%
Expected term (in years)	6.05			6.08
Expected dividend yield		—			—

Stock option activity under the 2020 Plan and 2022 Plan, are as follows:


	Stock Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (In Years)		Aggregate Intrinsic Value (In Thousands)
Outstanding as of December 31, 2022		3,341,834		$	9.52		8.7	$	12,877
Granted		1,421,936			13.70		—		—
Exercised		(100,351	)		2.12		—		—
Canceled/Forfeited		(430,216	)		12.13		—		—
Outstanding as of December 31, 2023		4,233,203		$	10.83		8.4	$	2,147
Vested and exercisable as of December 31, 2023		1,477,013		$	8.87		7.9	$	1,427
Vested and expected to vest as of December 31, 2023		4,233,203		$	10.83		8.4	$	2,147

The aggregate intrinsic value of stock options is calculated as the difference between the exercise prices of the stock options and the fair value of the Company's common stock for those stock options that had exercises prices lower than the fair value of the Company's common stock. The total intrinsic value of the stock options exercised during the years ended December 31, 2023 and 2022 was $1.4 million and $0.9 million, respectively. The intrinsic value is the difference between the estimated fair value of the Company’s common stock at the time of exercise and the exercise price of the stock option. During the years ended December 31, 2023 and 2022, the total proceeds to the Company from stock option exercises was $0.2 million and $0.2 million, respectively.

The weighted-average grant date fair value of stock options granted during the years ended December 31, 2023 and 2022 was $8.56 and $7.66 per share, respectively.

Stock-based compensation expense recognized for stock option grants included in the accompanying consolidated statements of operations and comprehensive loss is as follows (in thousands):


	Year Ended December 31,
	2023		2022
Research and development	$	2,966	$	1,695
General and administrative		4,082		3,068
Total stock-based compensation expense	$	7,048	$	4,763

The Company had 4,233,203 vested and unvested stock options outstanding as of December 31, 2023. As of December 31, 2023, total unrecognized compensation expense related to stock options was $20.2 million. This amount is expected to be recognized over a weighted average period of approximately 2.49 years.