During the three and six months ended June 30, 2023 and 2022, the Company granted the following stock options (in thousands):

The Company recognizes stock-based compensation expense for stock options granted to employees, directors and certain consultants. The Company estimates the fair value of stock options using the Black-Scholes option pricing model. The fair value of stock options granted is recognized as expense over the requisite service period on a straight-lined basis.

The following weighted-average assumptions were used for stock options granted during the three and six months ended June 30, 2023 and 2022:

The per-share weighted average grant-date fair value of stock options granted during the three and six months ended June 30, 2023 and 2022 was as follows:

	Three months ended June 30,				Six months ended June 30,
	2023		2022		2023		2022
Weighted average grant date fair value	$	1.64	$	9.97	$	2.99	$	23.68

Vesting of all stock option grants is subject to continuous service with the Company through such vesting dates. As of June 30, 2023, there were approximately 522,000 stock options outstanding.

During the six months ended June 30, 2022, the Company granted approximately 55,000 performance-based restricted stock units (“RSUs”), all of which were forfeited during 2022, as the applicable performance goals were not met. The Company did not grant any RSUs during the three months ended June 30, 2022 or during the three and six months ended June 30, 2023.

The Company recognizes the fair value of RSUs as expense on a straight-line basis over the requisite service period. For performance-based RSUs, the Company begins recognizing the expense once the achievement of the related performance goal is determined to be probable.

Outstanding RSUs are settled in an equal number of shares of common stock on the vesting date of the award. An RSU award is settled only to the extent vested. Vesting generally requires the continued employment or service by the award recipient through the respective vesting date. Because RSUs are settled in an equal number of shares of common stock without any offsetting payment by the recipient, the measurement of cost is based on the quoted market price of the stock at the measurement date, which is the grant date.

In lieu of paying cash to satisfy withholding taxes due upon the settlement of vested RSUs, at the Company’s discretion, an employee may elect to have shares of common stock withheld that would otherwise be issued at settlement, the value of which is equal to the amount of withholding taxes payable. During the three and six months ended June 30, 2023, less than 1,000 RSUs vested. During both the three and six months ended June 30, 2022, there were approximately 1,000 RSUs that vested. As of June 30, 2023, there were approximately 1,000 RSUs outstanding.

For the three and six months ended June 30, 2023 and 2022, the Company recognized stock-based compensation expense as follows (in thousands):