The Company had 4.5 million shares available for grant as of June 30, 2022 under the 2021 Equity Incentive Award Plan. The Company ceased making awards under the 2008 Stock Plan upon the effective date of the Company’s IPO.

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


	Six Months Ended
	June 30, 2022

	Number of Shares	Weighted Average Exercise Price
Outstanding, beginning of period	6,365	$	5.34
Granted	254	35.58
Exercised	(802)	3.57
Forfeited	(151)	7.09
Outstanding, end of period	5,666	6.90
Vested and expected to vest	5,666	6.90
Exercisable	2,933	4.63

As of June 30, 2022 and December 31, 2021, the aggregate pre-tax intrinsic value of options outstanding and exercisable was $82.3 million and $64.3 million, respectively, and the aggregate pre-tax intrinsic value options outstanding were $147.1 million and $125.7 million, respectively. The aggregate pre-tax intrinsic value of options exercised was $21.7 million and $3.4 million during the six months ended June 30, 2022 and 2021, respectively.

As of June 30, 2022, there was a total of $11.4 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 June 30,						Six Months Ended June 30,
	2022			2021			2022			2021

Expected life (years)	5.8			6.0			5.9			6.0
Expected volatility	56		%	52		%	55		%	49		%
Risk-free interest rate	2.9		%	1.1		%	2.5		%	1.1		%
Expected dividend rate	—		%	—		%	—		%	—		%
Weighted-average fair value	$	20.07		$	3.59		$	19.15		$	3.14

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


	Six Months Ended
	June 30, 2022

	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding, beginning of period	35	$	34.78
Awarded	538	34.14

Forfeited	(14)	31.76
Outstanding, end of period	559	34.22

As of June 30, 2022, there was a total of $17.8 million of unrecognized stock-based compensation expense related to RSUs.

As of June 30, 2022, there was approximately $0.7 million of unrecognized cost related to employee stock purchases under the Employee Stock Purchase Plan (“ESPP”). This cost is expected to be recognized over a weighted average period of 0.5 years. As of June 30, 2022, a total of 0.8 million shares were available for issuance under the ESPP.

The fair value of the awards granted under the ESPP for the six months ended June 30, 2022 to employees was estimated as of the grant date using the Black-Scholes model assuming the weighted-average assumptions listed in the following table:


	Six Months Ended June 30,
	2022

Expected life (years)	0.8
Expected volatility	57		%
Risk-free interest rate	1.8		%
Expected dividend rate	—		%
Weighted-average fair value	$	12.25


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021

Cost of sales	$	252	$	51	$	375	$	74
Research and development	553		155		853		307
Sales, general and administrative	1,871		519		3,000		994
Total stock-based compensation	$	2,676	$	725	$	4,228	$	1,375