In June 2021, the Company adopted the 2021 Equity Incentive Plan ("2021 Plan"), which on the date of the underwriting agreement related to the Company's IPO became effective with an initial reserve of 26,662,087 shares, plus any shares subject to outstanding awards granted under the 2018 Equity Incentive Plan ("2018 Plan") that, on or after the effectiveness of the 2021 Plan, terminate or expire before exercise or settlement, are not issued because the award is settled in cash, are forfeited because of the failure to vest, or are reacquired or withheld (or not issued) to satisfy a tax withholding obligation or the purchase or exercise price. In addition, the number of shares reserved for issuance under the 2021 Plan will automatically increase on January 1 of each year for a period of ten years, beginning on January 1, 2022 and continuing through January 1, 2031, in an amount equal to (1) 5% of the total number of shares of the Company's common stock outstanding on December 31 of the immediately preceding year, or (2) a lesser number of shares determined by the Company's board of directors no later than December 31 of the immediately preceding year. Under the 2021 Plan, the Company may grant incentive stock options, non-statutory stock options, RSAs, restricted stock units, stock appreciation rights, performance awards and other stock-based awards. Terms of stock awards, including vesting requirements, are determined by the Company's board of directors or by a committee authorized by the Company's board of directors, subject to provisions of the 2021 Plan. The term of any stock option granted under the 2021 Plan cannot exceed ten years. Generally, awards granted by the Company vest over four years, but may be granted with different vesting terms. In conjunction with adopting the 2021 Plan, the Company discontinued the 2018 Plan with respect to new equity awards.

As of September 30, 2021, 24.9 million shares were available for future issuance pursuant to the 2021 Plan.

In June 2021, the Company adopted the 2021 Employee Stock Purchase Plan ("2021 ESPP"), which became effective immediately prior to the execution of the underwriting agreement related to the Company's IPO with an initial reserve of 2,470,000 shares. 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 will automatically increase on

January 1 of each year for a period of ten years, beginning on January 1, 2022 and continuing through January 1, 2031, by the lesser of (1) 1% of the total number of shares of the Company's common stock outstanding on December 31 of the immediately preceding year, and (2) 4,940,000 shares; provided, however, that the Company's board of directors may act to provide a lesser increase in number of shares. The Company may specify offerings with durations not more than 27 months and may specify shorter purchase periods within each offering. No shares have been issued under the 2021 ESPP as of September 30, 2021.

In 2018, the Company established the 2018 Plan under which it may grant incentive stock options, non-statutory stock options, RSAs, restricted stock units, stock appreciation rights and other stock-based awards. Terms of stock awards, including vesting requirements, were determined by the Company's board of directors or by a committee authorized by the Company's board of directors, subject to provisions of the 2018 Plan. The term of any stock option granted under the 2018 Plan cannot exceed ten years. Generally, awards granted by the Company vest over four years, but may have been granted with different vesting terms. Pursuant to the terms of the 2021 Plan, any shares subject to outstanding options originally granted under the 2018 Plan that terminate, expire or lapse for any reason without the delivery of shares to the holder thereof shall become available for issuance pursuant to awards granted under the 2021 Plan. While no shares are available for future issuance under the 2018 Plan, it continues to govern outstanding equity awards granted thereunder.

Stock-based compensation expense by classification included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development	$	2,673	$	1,965	$	12,615	$	9,033
General and administrative		10,369		7,783		28,408		11,257
Total stock-based compensation expense	$	13,042	$	9,748	$	41,023	$	20,290

Stock-based compensation expense for the nine months ended September 30, 2021 includes the impact of an award accelerated in connection with the Company's IPO resulting in stock-based compensation expense of $2.6 million.

At September 30, 2021, total stock-based compensation cost related to unvested awards not yet recognized was $122.5 million, which is expected to be recognized over a remaining weighted-average period of 2.46 years.

A summary of the Company’s RSAs activity was as follows:


	Number of Shares			Weighted-Average Value at Grant Date Per Share
Unvested shares as of December 31, 2020		7,562,503		$	0.0001
Vested		(3,968,751	)	$	0.0001
Forfeited		(18,750	)	$	0.0001
Unvested shares as of September 30, 2021		3,575,002		$	0.0001

A summary of the Company’s stock option activity was as follows:


	Number of Stock Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Options outstanding as of December 31, 2020		34,413,889		$	3.33
Granted		12,521,501		$	9.00
Exercised		(776,449	)	$	2.63
Canceled or forfeited		(2,597,874	)	$	4.00
Options outstanding as of September 30, 2021		43,561,067		$	4.93		7.97	$	432,916
Options exercisable as of September 30, 2021		24,397,665		$	3.29		7.17	$	280,840

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 weighted-average assumptions:


	Nine Months Ended September 30,
	2021	2020
Risk-free interest rate	0.79%	0.99%
Expected volatility	79%	75%
Expected term (in years)	6.10	6.25
Expected dividend yield	0%	0%

The weighted-average grant date fair value of options granted for the nine months ended September 30, 2021 and 2020 was $6.55 per share and $3.21 per share, respectively.