In September 2023, the Company adopted the 2023 Equity Incentive Plan (the 2023 Plan) that became effective in connection with the Company’s IPO. The 2023 Plan provides for the grant of stock options, restricted stock awards, restricted stock unit awards, and other stock-based awards to employees, directors, and non-employee service providers of the Company.

Awards granted under the 2023 Plan expire no later than ten years from the date of grant. The price of stock options shall not be less than 100% of the estimated fair value on the date of grant and typically vest over a four-year period although may be granted with different vesting terms. The 2023 Plan initially reserved 16,373,061 shares of common stock for the issuance of future awards and provides for an automatic annual increase in the number of shares of common stock reserved for future issuance under the 2023 Plan.

In September 2023, the Company adopted the 2023 Employee Share Purchase Plan (the 2023 ESPP) that became effective in connection with the Company’s IPO. The 2023 ESPP initially reserved 1,526,984 shares of common stock for the issuance of future awards and provides for an automatic annual increase in the number of shares of common stock reserved for future issuance under the 2023 ESPP.

In January 2020, the Company adopted the 2020 Equity Incentive Plan (the 2020 Plan) that provides for the grant of stock options, restricted stock awards, restricted stock unit awards, and other stock-based awards to employees, directors, and non-employee service providers of the Company. The 2020 Plan was suspended in connection with the Company’s IPO and no further grants will be made under the 2020 Plan. The 2020 Plan continues to govern the terms and conditions of outstanding awards granted under the 2020 Plan.

Upon the closing of the BlackThorn acquisition in September 2020, the Company assumed BlackThorn’s 2015 Equity Incentive Plan (the 2015 Plan, and collectively with the 2020 Plan and 2023 Plan, the Plans), pursuant to which outstanding stock options previously granted under the 2015 Plan converted into stock options to purchase common stock of the Company, which remain subject to the terms and conditions of the 2015 Plan. The 2015 Plan was suspended in connection with the closing of the acquisition of BlackThorn in September 2020.

Stock Option Activity


	Outstanding Stock Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
	(in thousands, except per share amounts and years)
Outstanding as of December 31, 2023		13,783		$	6.39		8.7	$	146,966
Granted		2,841			17.43
Exercised		(525	)		3.51
Canceled and forfeited		(884	)		5.93
Expired		(85	)		3.37
Outstanding as of March 31, 2024		15,130		$	8.60		8.8	$	90,736
Vested as of March 31, 2024		3,667		$	4.43		7.6	$	34,256
Exercisable as of March 31, 2024		3,659		$	4.44		7.6	$	34,145

The stock option activity table above excludes options granted to purchase 446,068 shares of common stock that were originally granted with market conditions to one of the Company’s executives.

The Company’s Plans allow for the grant of restricted common stock and restricted stock units to certain employees, executives, non-employee scientific advisors, and third-party service providers. The restrictions lapse over time primarily according to service-based vesting conditions of each award. In the event of a voluntary or involuntary termination of the holder’s continuous provision of services to the Company, any unvested portion of the restricted stock award is automatically forfeited.

The following table summarizes the Company’s restricted stock activity:


	Shares of Restricted Common Stock			Weighted- Average Grant Date Fair Value Per Share		Shares of Restricted Stock Units			Weighted- Average Grant Date Fair Value Per Share
	(in thousands, except per share amounts)
Outstanding and unvested as of December 31, 2023		840		$	6.11		353		$	17.00
Granted		—		—			1,165			18.07
Vested		(190	)		0.26	—			—
Forfeited and canceled		—		—			(10	)		18.07
Outstanding and unvested as of March 31, 2024		650		$	7.81		1,508		$	17.83

The restricted stock activity table above excludes 254,896 shares of restricted common stock issued to certain of the Company’s scientific advisors which vest based on the achievement of certain performance conditions to be separately defined and approved by the Company’s board of directors. As the performance conditions had not been determined as of March 31, 2024, the criteria for establishing a grant date, and accordingly a measurement date, were not met as of that date.

In June 2021, the Company granted stock options to purchase 446,068 shares of its common stock to one of its executive officers with an exercise price of $2.52 per share that contained both market and service conditions (the Market Award). Subject to the holder’s continued service, the Market Award provided for vesting in four equal tranches once the Company’s stock price exceeded certain thresholds. The original grant-date fair value of the Market Award of $0.9 million was determined using a Monte Carlo simulation model using an expected volatility of 100.0% and risk-free rate of 1.6%.

In January 2022, the Company amended the terms of the Market Award such that the award would vest in three modified tranches. One tranche of 223,034 stock options was based on a performance condition and two tranches of 111,517 stock options each were based on revised Company stock price thresholds and/or vesting schedules, subject to the holder’s continued service. The modification resulting in a performance-based tranche was determined to be a probable-to-improbable modification and the modification resulting in two revised market-based tranches were determined to be probable-to-probable modifications. The modification resulted in $0.3 million in total incremental expense.

In June 2023, the Company amended the terms such that vesting schedule for the two tranches of 111,517 stock options each that were based on the Company stock price thresholds would instead vest monthly over 3 years, subject to the holder’s continued service. The modification of the two market-based tranches were deemed to be probable-to-probable modifications. The modification resulted in $0.1 million in total incremental expense.

The unrecognized original grant-date fair value, together with incremental expense, is recognized as compensation for each tranche over the requisite service period. For the three months ended March 31, 2024 stock-based compensation related to the tranches was $0.1 million, including expense related to the performance-based tranche for which the condition was met upon completion of the Company's IPO. For the three months ended March 31, 2023, stock-based compensation related to the market-based tranches was not material and no expense was recognized for the performance-based tranche as the performance condition was not probable of being met.

In 2020, the Company approved grants of 700,965 stock options and 892,136 shares of restricted common stock to certain of the Company’s scientific advisors, which vest based on the achievement of performance conditions to be determined and continued service to the Company.

As of March 31, 2024, the Company’s board of directors established performance conditions for 401,462 stock options, such that the criteria for establishing a grant date, and accordingly a measurement date, were met for these performance stock options and the remaining 299,503 stock options with performance conditions to be established were cancelled in July 2023 because certain of the Company’s scientific advisors were terminated. Further, as of March 31, 2024, the performance conditions for 382,344 shares of

restricted common stock were established, 254,896 shares of restricted common stock with performance conditions to be established were cancelled in July 2023 because the consulting agreements with certain of the Company’s scientific advisors were terminated, and the performance conditions for the remaining 254,896 shares of restricted common stock have yet to be established.

The following table summarizes total stock-based compensation included in the Company’s condensed consolidated statements of operations and comprehensive loss:


	Three Months Ended March 31,
	2024		2023
	(in thousands)
Research and development	$	2,812	$	1,403
General and administrative		4,561		792
Total stock-based compensation	$	7,373	$	2,195

As of March 31, 2024, there was $89.7 million and $28.2 million of unrecognized stock-based compensation related to stock options and restricted stock outstanding, respectively, including stock options and restricted common stock for which achievement of milestones was not probable, which were expected to be recognized over a weighted-average remaining service period of 2.6 years and 3.4 years, respectively.