Equity Incentive Plan

6 Months Ended

Jun. 30, 2025

9. Equity Incentive Plan

Option Plan Activity

The following table summarizes the stock option activity for the six months ended June 30, 2025:


	Shares (in thousands)			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)
Outstanding at December 31, 2024		26,082		$	4.46		7.80
Granted		6,061		$	1.85
Exercised		(278	)	$	1.47
Expired and forfeited		(2,168	)	$	10.31
Outstanding at June 30, 2025		29,697		$	3.53		7.90

We estimated the fair value of each option grant on the grant date using the Black-Scholes option pricing model and for market-based stock option grants using the Monte Carlo simulation model. The following are the weighted-average assumptions:


	For the Six Months Ended
	June 30,
	2025			2024
Risk-free interest rate		4.3	%		4.2	%
Dividend yield		0.0	%		0.0	%
Volatility		80.1	%		74.9	%
Expected life (years)	6 to 10			6 to 10

The following table summarizes the restricted stock unit activity ("RSUs") for the six months ended June 30, 2025:


	Shares (in thousands)			Weighted-Average Grant Date Fair Value
Outstanding at December 31, 2024		1,981		$	2.35
Granted		2,807		$	1.84
Released		(458	)	$	2.06
Expired and forfeited		(197	)	$	2.58
Outstanding at June 30, 2025		4,133		$	1.97

The fair value of RSUs is estimated based on the closing market price of our common stock on the date of the grant. RSUs generally vest quarterly over a four-year period.

We estimated the fair value of each purchase right granted under our 1997 Employee Stock Purchase Plan, as amended, at the beginning of each new offering period using the Black-Scholes option pricing model. The following are the weighted average assumptions:


	For the Six Months Ended
	June 30,
	2025			2024
Risk-free interest rate		4.2	%		5.4	%
Dividend yield		0.0	%		0.0	%
Volatility		79.1	%		83.6	%
Expected life (months)		6			6

Stock-Based Compensation

The following table summarizes stock-based compensation expense related to stock-based payment awards granted pursuant to all of our equity compensation arrangements (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2025		2024		2025		2024
Research and development	$	276	$	553	$	521	$	1,254
General and administrative		1,825		2,060		3,396		3,938
Sales and marketing		696		1,957		1,391		2,753
Total stock-based compensation expense	$	2,797	$	4,570	$	5,308	$	7,945

As of June 30, 2025, there was $26.8 million of total unrecognized compensation cost related to non-vested, stock-based payment awards granted under all of our equity compensation plans and all non-plan option grants. Total unrecognized compensation cost will be adjusted for future changes in estimated forfeitures. We expect to recognize this compensation cost over a weighted-average period of three years.