In February 2021, the Company adopted the 2021 Incentive Award Plan (2021 Plan) and the 2021 Employee Stock Purchase Plan (2021 ESPP), both of which became effective on the completion of the Company’s IPO. The 2021 Plan provides for a variety of stock-based compensation awards, including stock options, restricted stock awards (RSAs), and restricted stock units (RSUs). The 2021 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their earnings, subject to plan limitations. Unless otherwise determined by the Company’s board of directors, employees may purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first date of an offering period or on the purchase date. As of September 30, 2022, 12.6 million shares and 3.6 million shares were available for future issuance under the 2021 Plan and the 2021 ESPP, respectively.

Stock-based compensation expense is recognized in the statements of operations as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
	(in thousands)
Research and development	$	7,437	$	4,072	$	20,557	$	9,888
General and administrative		2,643		1,878		7,189		5,161
Total stock-based compensation expense	$	10,080	$	5,950	$	27,746	$	15,049

Unrecognized stock-based compensation costs related to unvested awards and the weighted-average period over which the costs are expected to be recognized as of September 30, 2022 are as follows:

	Stock Options		RSAs		RSUs
Unrecognized stock-based compensation expense (in thousands)	$	92,582	$	860	$	5,317
Weighted-average period costs expected to be recognized (in years)		2.8		1.0		2.5

	Stock Options (in thousands)			Weighted-Average Exercise Price per Share		Weighted-Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2021		17,337		$	8.96		8.7	$	141,718
Granted		11,375			6.15
Exercised		(983	)		2.16
Forfeited/Cancelled		(2,187	)		8.53
Outstanding as of September 30, 2022		25,542		$	8.00		8.6	$	24,279
Exercisable as of September 30, 2022		6,604		$	6.90		7.8	$	13,114

The fair value of stock options granted to employees, directors, and consultants was estimated on the date of grant using the Black-Scholes option pricing model using the following assumptions:

	Nine Months Ended September 30,
Assumptions	2022	2021
Risk free interest rate	1.56% - 3.94%	0.46% - 1.15%
Expected volatility	70%	70%
Expected term (years)	5.50 - 6.25	5.50 - 6.40
Expected dividend	0%	0%

The following table summarizes additional information related to stock option activity:

	Nine Months Ended September 30,
	2022		2021
Weighted average grant date fair value per share for options granted	$	3.96	$	14.64
Aggregate intrinsic value of stock options exercised (in thousands)	$	5,854	$	22,187

	RSAs (in thousands)			RSAs Weighted-Average Grant Date Fair Value per Share		RSUs (in thousands)			RSUs Weighted-Average Grant Date Fair Value per Share
Unvested shares as of December 31, 2021		4,365		$	0.43		141		$	9.43
Granted		-			-		983			6.33
Vested		(3,530	)		0.28		(59	)		8.56
Forfeited		(29	)		-		(88	)		4.66
Unvested shares as of September 30, 2022		806		$	1.13		977		$	6.82

The fair value of RSAs vested during the nine months ended September 30, 2022 and 2021 was $1.0 million and $1.1 million, respectively. The fair value of RSUs vested during the nine months ended September 30, 2022 and 2021 was $0.4 million and $0.3 million, respectively.