The Company's 2015 Long-Term Incentive Plan ("2015 Stock Plan") and 2021 Incentive Award Plan (“2021 Stock Plan” and, together, “Stock Plans”) permit the grant of restricted stock units (“RSUs”), stock options, and other stock-based awards to employees, non-employee directors, and consultants.

The following table summarizes the Company’s stock option and restricted stock unit activity during the nine months ended September 30, 2023:


	Stock Options						RSUs
	Number of Shares (in millions)	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in millions)		Number of Shares (in millions)	Weighted-Average Grant-Date Fair Value
Outstanding at December 31, 2022	61	$	12.98				37	$	38.72
Granted	3	$	17.31				58	$	14.86
Exercised / Vested	(2)	$	4.45				(25)	$	24.66
Forfeited / Cancelled	—	$	—				(8)	$	33.82

Outstanding at September 30, 2023	62	$	13.42	6.2	$	692	62	$	22.61
Vested and expected to vest at September 30, 2023	62	$	13.42	6.2	$	692	62	$	22.61
Exercisable at September 30, 2023	30	$	5.35	5.1	$	574	—	$	—

The following table summarizes the Company’s stock-based compensation expense for the Stock Plans and 2021 Employee Stock Purchase Plan (“ESPP”) by line item in the Condensed Consolidated Statements of Operations (in millions):




	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2023		2022		2023
Cost of revenues	$	25	$	23	$	48	$	64
Research and development	133		133		386		289
Selling, general, and administrative	135		86		418		253
Total stock-based compensation expense	$	293	$	242	$	852	$	606

As of September 30, 2023, the Company’s unrecognized stock-based compensation expense for unvested awards was approximately $1,358 million, which is expected to be recognized over a weighted-average period of 5.5 years and 1.9 years for stock options and RSUs outstanding, respectively.