The 2020 Equity Incentive Plan (the “2020 Plan”) was approved by the board of directors on September 24, 2020. The 2020 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights to the Company’s officers, employees, directors and consultants. The number of shares of common stock initially reserved for issuance under the 2020 Plan was 4,406,374, which shall be increased, upon approval by the board of directors, on January 1, 2021 and each January 1 thereafter, in an amount equal to the least of (i) 4,406,374 shares of common stock, (ii) five percent (5%) of the outstanding common stock on the immediately preceding December 31, or (iii) such number of common stock determined by the board of directors no later than the immediately preceding December 31. For 2022, the board’s compensation committee, as the 2020 Plan administrator, exercised its discretion under clause (iii) to increase the number of shares of common stock reserved for issuance under the 2020 Plan by a lesser amount of 1,363,084 shares, effective as of January 1, 2022. For 2023, the board’s compensation committee, as the 2020 Plan administrator, exercised its discretion under clause (iii) to increase the number of shares of common stock reserved for issuance under the 2020 Plan by a lesser amount of 1,830,853 shares, effective as of January 1, 2023. As of December 31, 2022, there were 4,618,292 shares available for issuance under the 2020 Plan.

On September 9, 2022, the Company granted 374,899 Restricted Stock Units (RSUs) to employees pursuant to an employee retention program approved by the Board's compensation committee. The RSU’s have graded vesting on an annual basis for two years of continuous service, as per the 2020 Plan.

The table below summarizes the annual grant activity under the 2020 Plan as of December 31, 2022:


	Shares Available for Grant
Balances, December 31, 2021		4,951,680
Shares reserved for issuance		1,363,084
Options granted		(1,419,197	)
RSU’s granted		(374,899	)
Options forfeited / cancelled		97,624
Balances December 31, 2022		4,618,292

The 2020 Employee Stock Purchase Plan (the “2020 ESPP”) was approved by the board of directors on September 24, 2020. A total of 400,752 shares of common stock were initially reserved for issuance under this plan, which shall be increased, upon approval by the board of directors, on January 1, 2021 and each January 1 thereafter, to the lesser of (i) 801,504 shares of common stock, (ii) 1% of the outstanding shares of common stock on the last day of the immediately preceding fiscal year, or (iii) an amount determined by the board of directors or any of its committees no later than the last day of the immediately preceding fiscal year. For 2022, the board waived the annual increase to the shares reserved under the 2020 ESPP. For 2023, the 2020 ESPP reserved shares were increased under clause (iii) by 457,713 shares, effective as of January 1, 2023. On May 20, 2022, employees exercised their right to purchase 18,454 shares under the 2020 ESPP. On November 21, 2022, employees exercised their right to purchase 30,385 shares under the 2020 ESPP. As of December 31, 2022, 95,905 shares are issued or outstanding, and there were 705,559 shares available for issuance, under the 2020 ESPP.

In 2013, the Company adopted the 2013 Stock Plan (the “2013 Plan”). On September 24, 2020, this plan was replaced by the 2020 Plan, and future issuances of incentive instruments will be governed by that plan. Subject to the provisions of the 2020 Plan, the Company had the option to either forfeit or repurchase remaining shares under the 2013 Equity Incentive Plan on or after the registration date. The Company chose to forfeit the remaining shares.

The following table presents RSU activity under the 2020 Plan as of December 31, 2022:


	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2021		—	$	—
Granted		374,899		13.6
Unvested shares at December 31, 2022		374,899	$	13.6

As of December 31, 2022, there was $4,317 of unrecognized compensation cost related to RSUs that are expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 1.7 years.

The following table summarizes option activity for the year ended December 31, 2022:


	Options Outstanding
						Weighted- Average
				Weighted		Remaining		Aggregate
	Number			Average		Contractual		Intrinsic
	of			Exercise		Life		Value
	Options			Price		(in years)		(in 000s)
Balances, December 31, 2021		4,246,007		$	8.22		6.86	$	68,506
Options granted		1,419,197		$	15.83
Options forfeited / cancelled		(97,624	)	$	20.04
Options exercised		(288,809	)	$	1.67
Balances December 31, 2022		5,278,771		$	10.40		6.82	$	17,244
At December 31, 2022
Vested and expected to vest		5,278,771		$	10.40		6.82	$	17,244
Exercisable		3,281,213		$	6.91		5.76	$	15,520

The weighted average grant date fair value of stock options granted during the year ended December 31, 2022 and 2021 was $10.92 and $20.03, respectively.

The aggregate intrinsic value of options vested and exercisable as of December 31, 2022 and 2021 is calculated based on the difference between the exercise price and the fair value of our common stock. The intrinsic value of options exercised in 2022 and 2021 was $3,764 and $18,534, respectively.

As of December 31, 2022, the total compensation cost related to nonvested service-based awards not yet recognized is $21,005. The weighted-average period over which the nonvested awards is expected to be recognized is 2.8 years.

The Company estimated the fair value of stock options using the Black-Scholes options valuation model. The fair value of employee stock options is being amortized on a straight-line basis over the requisite service period of the awards. The fair value of employee stock options was estimated using the following assumptions:


	Year Ended December 31,
	2022	2021	2020
Risk-free interest rate	1.48% - 4.34%	0.35% - 1.30%	0.31% - 1.51%
Expected life (in years)	5.50 - 6.44	5.50 - 6.44	4.92 - 6.40
Dividend yield	0%	0%	0%
Expected volatility	76.33% - 81.00%	76.50% - 79.90%	70.70% - 77.60%

The weighted average assumptions used to estimate the fair value of stock purchase rights under the 2020 ESPP are as follows:


	Year Ended December 31,
	2022	2021
Risk-free interest rate	3.44%	0.0004
Expected life (in years)	0.49	0.5
Dividend yield	0%	0%
Expected volatility	77.00%	77.83%

Expected Term: The Company uses the simplified method to calculate expected term described in the SEC’s Staff Accounting Bulletin No. 107, which takes into account vesting term and expiration date of the options.

Volatility: Volatility is based on an average of the historical volatilities of comparable publicly traded companies for the expected term.

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

Dividend Yield: The Company has never declared or paid any cash dividends and does not plan to pay cash dividends in the foreseeable future, and therefore, used an expected dividend yield of zero in the valuation model.

Stock-based compensation expense recorded under ASC 718 was allocated to research and development and general and administrative expense as follows:


	For the Years Ended December 31,
	2022		2021		2020
Research and development	$	3,466	$	1,440	$	836
General and administrative		6,729		3,900		1,097
Total stock-based compensation	$	10,195	$	5,340	$	1,933

Stock-based compensation expense by award type included within the condensed consolidated statements of operations is as follows:


	For the Years Ended December 31,
	2022		2021		2020
Stock options	$	9,174	$	4,938	$	1,933
Restricted stock units		790		—		—
Employee stock purchase plan		231		402		—
Total stock-based compensation	$	10,195	$	5,340	$	1,933