As of June 30, 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 and approved by the Company’s stockholders 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 June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Incentive Plan	$	10,934	$	10,236	$	22,500	$	21,297
Inducement Plan	2,084		2,245		4,007		4,720
ESPP	155		360		318		831
Stock-based compensation expense	$	13,173	$	12,841	$	26,825	$	26,848


	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	461	6.30
Exercised	(108)	3.25			$	257
Cancelled or Forfeited	(2,029)	9.67
Outstanding at June 30, 2024	33,829	$	8.14	6.39	$	13,242
Exercisable at June 30, 2024	20,789	$	7.86	5.11	$	13,242
Vested and expected to vest at June 30, 2024	31,313	$	8.07	6.28	$	13,242


	Shares (in thousands)	Weighted Average Grant Date Fair Value
Unvested at December 31, 2023	5,592	$	8.67
Granted	259	5.80
Vested	(256)	9.74
Forfeited	(446)	8.80
Unvested at June 30, 2024	5,149	$	8.46

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 six months of 2024 and 2023 was $5.80 and $9.18, 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 June 30, 2024, total unrecognized compensation cost related to unvested restricted stock unit awards granted under the Incentive Plan was $29,926, which is expected to be recognized over a weighted average period of 1.6 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	293	5.40
Exercised	(148)	3.14			$	320
Cancelled or Forfeited	(488)	10.78
Outstanding at June 30, 2024	5,184	$	8.55	7.35	$	4,589
Exercisable at June 30, 2024	2,753	$	7.22	6.50	$	3,968
Vested and expected to vest at June 30, 2024	4,708	$	8.38	7.26	$	4,460


	Shares (in thousands)	Weighted Average Grant Date Fair Value
Unvested at December 31, 2023	915	$	9.90
Granted	164	5.36
Vested	(99)	10.36
Forfeited	(143)	9.92
Unvested at June 30, 2024	837	$	8.95

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 six months of 2024 and 2023 was $5.36 and $8.84, 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 June 30, 2024, total unrecognized compensation cost related to unvested restricted stock unit awards granted under the Inducement Plan was $5,314, 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.

The following table summarizes the key assumptions used by the Company to value the stock option awards granted under the Incentive Plan during the six months ended June 30, 2024 and 2023:


	Six Months Ended June 30,
	2024			2023
Expected Life in Years	5.8			5.5
Expected Volatility	83.7		%	84.3		%
Expected Dividend Yield	0.0		%	0.0		%
Risk-Free Interest Rate	4.3		%	3.9		%
Weighted average grant date fair value per share	$	4.56		$	6.40

As of June 30, 2024, total unrecognized compensation cost related to unvested stock option awards granted under the Incentive Plan was $54,665, which is expected to be recognized over a weighted average period of 1.4 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 six months ended June 30, 2024 and 2023:


	Six Months Ended June 30,
	2024			2023
Expected Life in Years	5.8			5.5
Expected Volatility	83.3		%	84.3		%
Expected Dividend Yield	0.0		%	0.0		%
Risk-Free Interest Rate	4.4		%	3.8		%
Weighted average grant date fair value per share	$	3.90		$	6.38

As of June 30, 2024, total unrecognized compensation cost related to unvested stock option awards granted under the Inducement Plan was $11,075, which is expected to be recognized over a weighted average period of 1.4 years.