Prior to May 10, 2022, the Company granted RSUs to employees and directors under the 2014 Stock Incentive Plan (the “2014 Plan”). Following shareholder approval of the 2022 Stock Incentive Plan (the “2022 Plan” and, together with the 2014 Plan, the “Plans”) on May 10, 2022, the Company discontinued granting RSUs to employees and directors under the 2014 Plan and began granting them under the 2022 Plan. The Plans are administered by the Compensation Committee of the Company’s Board of Directors. The Plans are intended to attract and retain employees and directors, and to provide an incentive for these individuals to assist the Company to achieve long-range performance goals and enable these individuals to participate in the long-term growth of the Company.

The total stock-based compensation expense included in the Company’s condensed consolidated statements of operations and comprehensive income (loss) was as follows:


	Three Months Ended March 31,
	2024		2023
Cost of revenues	$	1	$	1
Research and development		2		1
Selling, general and administrative		12		16
Total stock-based compensation expense	$	15	$	18

At March 31, 2024, the total compensation expense related to unvested stock-based awards granted to employees and directors under the Plans that had not been recognized was $41. Stock-based awards include (i) time-based RSUs, (ii) performance-based RSUs based on the achievement of adjusted EBITDA targets (the “Adjusted EBITDA RSUs”), (iii) performance-based RSUs based on the Company’s total shareholder return relative to a group of peers over a three-year performance period (the “rTSR RSUs”) and (iv) employee stock purchase plan rights. The Company determines the fair value of time-based RSUs based on the closing market price of the Company’s common stock on the date of the award. The Company determines the original fair value of Adjusted EBITDA RSUs based upon the closing market price of the Company’s stock on the date of the award, and adjusts the fair value quarterly during the first year based upon actual and forecasted results against Adjusted EBITDA targets. The Company estimates the fair value of rTSR RSUs using the Monte Carlo simulation model, which requires the use of highly subjective and complex assumptions, including the price volatility of the underlying stock. The Company estimates the fair value of employee stock purchase plan rights using the Black-Scholes valuation method. Such values are recognized as expense on a straight-line basis for time-based awards and rTSR RSUs and using the accelerated graded vesting method for Adjusted EBITDA RSUs, all over the requisite service periods.

The following table presents the activity for RSUs under the Plans:


	Three Months Ended March 31, 2024
	Quantity			Weighted Average Grant Date Fair Value Per Share
RSUs – beginning of period		1.0		$	98.36
Granted		0.1		$	129.92
Vested or forfeited		(0.2	)	$	112.27
RSUs – end of period		0.9		$	99.09