In February 2021, the Company adopted the 2021 Incentive Award Plan, which became effective on the completion of the Company’s IPO. The 2021 Incentive Award Plan provides for a variety of stock-based compensation awards, including stock options, restricted stock awards (RSAs), and restricted stock units (RSUs). In conjunction with adopting the 2021 Incentive Award Plan, the Company discontinued the 2018 Equity Incentive Plan with respect to new equity awards. The number of shares of the Company’s common stock reserved for issuance is subject to automatically increase by 5% of all shares outstanding at the beginning of each calendar year.

In February 2021, the Company adopted the 2021 Employee Stock Purchase Plan (2021 ESPP), which became effective on the completion of the Company’s IPO. 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 are able to 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 or on the purchase date. The number of shares of the Company’s common stock reserved for issuance under the 2021 ESPP is subject to automatically increase by 1% of all shares outstanding at the beginning of each calendar year. The Company may specify offerings with durations of not more than 27 months and may specify shorter purchase periods within each offering.

In October 2018, the Company adopted the 2018 Equity Incentive Plan (2018 Plan), under which it may grant incentive stock options, non-statutory stock options, RSAs, RSUs, and other stock-based awards to any person, including officers, directors, and consultants. Terms of stock agreements, including vesting requirements, are determined by the Company’s board of directors, or by a committee appointed by the board of directors, subject to the provisions of the 2018 Plan. The 2018 Plan terminated as of the adoption of the 2021 Incentive Award Plan.

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
	(in thousands)
Research and development	$	4,072	$	980	$	9,888	$	2,555
General and administrative		1,878		186		5,161		482
Total stock-based compensation expense	$	5,950	$	1,166	$	15,049	$	3,037

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, 2021 are as follows:

	Stock Options		RSAs		RSUs
Unrecognized stock-based compensation expense (in thousands)	$	79,637	$	2,166	$	887
Weighted-average period costs expected to be recognized (years)		2.8		1.1		1.5

	Stock Options (in thousands)			Weighted- Average Exercise Price per Share		Weighted-Average Remaining Contractual Life (years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2020		15,677		$	4.52
Granted		3,398			23.26
Exercised		(1,121	)		1.99
Forfeited/Cancelled		(671	)		5.05
Outstanding as of September 30, 2021		17,283		$	8.34		8.9	$	244,590
Exercisable as of September 30, 2021		2,874		$	2.05		8.2	$	58,832

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	2021			2020
Risk free interest rate	0.46% - 1.15%			0.36% - 1.51%
Expected volatility		70	%		70	%
Expected term (years)	5.50 - 6.40			6.25 - 6.75
Expected dividend		0	%		0	%

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

	Nine Months Ended September 30,
	2021		2020
Weighted average grant date fair value per share for options granted	$	14.64	$	0.54
Aggregate intrinsic value of stock options exercised (in thousands)	$	22,187	$	205

	RSAs (in thousands)			Weighted-Average Grant Date Fair Value per Share
Unvested shares as of December 31, 2020		10,079		$	0.33
Vested		(4,273	)		0.25
Forfeited		(15	)		0.73
Unvested shares as of September 30, 2021		5,791		$	0.39

The fair value of vested RSAs for the three months ended September 30, 2021 and 2020 was $0.4 million and $0.2 million, respectively, and $1.1 million and $0.6 million for the nine months ended September 30, 2021 and 2020, respectively. As of December 31, 2020, there were 0.3 million RSUs unvested. During the nine months ended September 30, 2021 there were 0.1 million granted, 0.2 million vested. As of September 30, 2021, there are 0.2 million RSUs unvested.