As of March 31, 2024, the Company had three stock-based employee compensation plans: the Amended and Restated Stock Incentive Plan (“Incentive Plan”), the Amended and Restated Inducement Equity Incentive Plan (“Inducement Plan”) and the Amended and Restated Employee Stock Purchase Plan (“ESPP”). The Incentive Plan was most recently amended and restated on April 22, 2024, subject to stockholder approval at the Company’s annual meeting of stockholders to be held on June 12, 2024. The Inducement Plan was most recently amended and restated by the Company’s Board of Directors on October 26, 2023. The ESPP was most recently amended and restated by the Company’s Board of Directors on July 7, 2023.


	Three Months Ended March 31,
	2024		2023
Incentive Plan	$	11,566	$	11,061
Inducement Plan	1,923		2,475
ESPP	163		471
Stock-based compensation expense	$	13,652	$	14,007


	Shares (in thousands)	Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2023	35,505	$	8.24
Granted	—	—
Exercised	(48)	3.27			$	103
Cancelled or Forfeited	(1,068)	9.60
Outstanding at March 31, 2024	34,389	$	8.20	6.61	$	6,951
Exercisable at March 31, 2024	20,922	$	7.88	5.30	$	6,951
Vested and expected to vest at March 31, 2024	31,784	$	8.13	6.49	$	6,951


	Shares (in thousands)	Weighted Average Grant Date Fair Value
Unvested at December 31, 2023	5,592	$	8.67
Granted	128	5.30
Vested	(96)	12.30
Forfeited	(313)	8.65
Unvested at March 31, 2024	5,311	$	8.52

For restricted stock unit awards granted under the Incentive Plan, the fair value of the awards is determined based on the market value of the Company’s shares on the grant date. The weighted average grant date fair value of these awards granted during the first three months of 2024 and 2023 was $5.30 and $10.32, respectively. The fair value of the restricted stock unit awards is amortized to expense over the vesting periods using a straight-line expense attribution method.

As of March 31, 2024, total unrecognized compensation cost related to unvested restricted stock unit awards granted under the Incentive Plan was $33,457, which is expected to be recognized over a weighted average period of 1.8 years.


	Shares (in thousands)	Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2023	5,527	$	8.77
Granted	92	5.25
Exercised	(128)	3.09			$	274
Cancelled or Forfeited	(300)	10.86
Outstanding at March 31, 2024	5,191	$	8.73	7.53	$	2,454
Exercisable at March 31, 2024	2,628	$	7.53	6.76	$	2,128
Vested and expected to vest at March 31, 2024	4,684	$	8.59	7.46	$	2,373


	Shares (in thousands)	Weighted Average Grant Date Fair Value
Unvested at December 31, 2023	915	$	9.90
Granted	63	5.25
Vested	(59)	11.96
Forfeited	(106)	10.41
Unvested at March 31, 2024	813	$	9.32

For restricted stock unit awards granted under the Inducement Plan, the fair value of the awards is determined based on the market value of the Company’s shares on the grant date. The weighted average grant date fair value of these awards granted during the first three months of 2024 and 2023 was $5.25 and $9.64, respectively. The fair value of the restricted stock unit awards is amortized to expense over the vesting periods using a straight-line expense attribution method.

As of March 31, 2024, total unrecognized compensation cost related to unvested restricted stock unit awards granted under the Inducement Plan was $5,588, which is expected to be recognized over a weighted average period of 1.7 years.

For stock option awards granted under the Incentive Plan and the Inducement Plan, the fair value is estimated on the date of grant using a Black-Scholes option pricing model and the assumptions noted below. The fair value of the stock option awards is amortized to expense over the vesting periods using a straight-line expense attribution method.

There were no stock option awards granted under the Incentive Plan during the three months ended March 31, 2024. The following table summarizes the key assumptions used by the Company to value the stock option awards granted under the Incentive Plan during the three months ended March 31, 2023:


	Three Months Ended March 31, 2023
Expected Life in Years	5.5
Expected Volatility	84.2		%
Expected Dividend Yield	0.0		%
Risk-Free Interest Rate	3.6		%
Weighted average grant date fair value per share	$	7.47

As of March 31, 2024, total unrecognized compensation cost related to unvested stock option awards granted under the Incentive Plan was $62,593, which is expected to be recognized over a weighted average period of 1.6 years.

The following table summarizes the key assumptions used by the Company to value the stock option awards granted under the Inducement Plan during the three months ended March 31, 2024 and 2023:


	Three Months Ended March 31,
	2024			2023
Expected Life in Years	5.8			5.5
Expected Volatility	82.8		%	84.2		%
Expected Dividend Yield	0.0		%	0.0		%
Risk-Free Interest Rate	4.1		%	3.7		%
Weighted average grant date fair value per share	$	3.77		$	6.85

As of March 31, 2024, total unrecognized compensation cost related to unvested stock option awards granted under the Inducement Plan was $12,326, which is expected to be recognized over a weighted average period of 1.4 years.