The Company had 5.3 million shares available for grant as of September 30, 2023 under the 2021 Equity Incentive Award Plan.

A summary of the Company’s stock option activity and related information are as follows (shares in thousands):


	Nine Months Ended
	September 30, 2023

	Number of Shares	Weighted-Average Exercise Price
Outstanding, beginning of period	5,353	$	6.93
Granted	398	36.83
Exercised	(323)	4.67
Forfeited	(14)	11.01
Outstanding, end of period	5,414	9.26
Vested and expected to vest	5,414	9.26
Exercisable	3,961	6.50

As of September 30, 2023 and December 31, 2022, the aggregate pre-tax intrinsic value of options outstanding and exercisable was $106.8 million and $126.3 million, respectively, and the aggregate pre-tax intrinsic value of options outstanding were $130.0 million and $185.3 million, respectively. The aggregate pre-tax intrinsic value of options exercised was $8.9 million and $27.9 million during the nine months ended September 30, 2023 and 2022, respectively.

As of September 30, 2023, there was a total of $12.4 million of unrecognized stock-based compensation expense related to stock options.

The fair value of the options granted to employees or directors was estimated as of the grant date using the Black-Scholes model assuming the weighted-average assumptions listed in the following table:


	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022

Expected life (years)	0.0			0.0			6.0			5.9
Expected volatility	—		%	—		%	57		%	55		%
Risk-free interest rate	—		%	—		%	4.0		%	2.5		%
Expected dividend rate	—		%	—		%	—		%	—		%
Weighted-average fair value	$	—		$	—		$	21.02		$	19.15

A summary of the Company’s restricted stock unit or RSU activity and related information are as follows (shares in thousands):


	Nine Months Ended
	September 30, 2023

	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding, beginning of period	742	$	36.35
Awarded	1,031	36.54

Forfeited	(86)	35.00
Vested	(169)	35.87
Outstanding, end of period	1,518	36.61

As of September 30, 2023, there was a total of $47.5 million of unrecognized stock-based compensation expense related to RSUs.

As of September 30, 2023, there was approximately $1.2 million of unrecognized cost related to the Company’s Employee Stock Purchase Plan, or ESPP. This cost is expected to be recognized over a weighted average period of 0.4 years. As of September 30, 2023, a total of 1.1 million shares were available for issuance under the ESPP.

The fair value of the awards granted under the ESPP for the nine months ended September 30, 2023 to employees was estimated as of the grant date using the Black-Scholes model assuming the weighted-average assumptions listed in the following table:


	Nine Months Ended September 30,
	2023

Expected life (years)	0.8
Expected volatility	55		%
Risk-free interest rate	5.0		%
Expected dividend rate	—		%
Weighted-average fair value	$	11.28


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022

Cost of sales	$	660	337		$	1,730	712
Research and development	1,375		678		3,506		1,531
Sales, general and administrative	3,922		2,210		10,509		5,209
Stock-based compensation capitalized in inventory	(631)		—		(1,592)		—
Total stock-based compensation	$	5,326	$	3,225	$	14,153	$	7,452