Stock Based Compensation

3 Months Ended

Mar. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock Based Compensation

6. Stock Based Compensation

Stock-based Compensation Expenses

The following tables present the Company's stock-based compensation for stock-settled awards by type (i.e., stock options and restricted stock units (“RSUs”)) granted under the Company's incentive plans, and rights to purchase shares of common stock issued under the Company's Employee Stock Purchase Plan (“ESPP”) and financial statement lines included in the accompanying unaudited condensed consolidated statement of operations and comprehensive loss for the three months ended March 31:

	Three months ended March 31,
	2023		2022
	(in thousands)
Options	$	831	$	883
RSUs		1,066		511
ESPP	45			—
Total stock-based compensation expense	$	1,942	$	1,394
	Three months ended March 31,
	2023		2022
	(in thousands)
Cost of sales	$	148	$	101
Selling, general and administrative		1,562		978
Research and development		232		315
Total stock-based compensation expense	$	1,942	$	1,394

Compensation cost related to unvested stock options and RSUs will generally be amortized on a straight-line basis over the remaining average service period. The following table presents the unamortized compensation cost and weighted average service period of all unvested outstanding awards as of March 31, 2023.

	Unamortized Compensation Costs		Weighted Average Service Period
	(in thousands)		(years)
Options	$	4,978	2.1
RSUs		13,456	3.2
Total unamortized compensation cost	$	18,434

Plan Activities

The following table summarizes stock option activity under the Company's incentive plans:

	Number of Shares			Weighted Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life	Aggregate Intrinsic Value
						(in years)	(in thousands)
Options outstanding, December 31, 2022		2,756,368		$	2.83
Forfeited		(4,333	)	$	2.34
Expired		(3,541	)	$	2.34
Options outstanding, March 31, 2023		2,748,494		$	2.84	6.7	$	192
Options vested and exercisable, March 31, 2023		1,724,176		$	2.74	5.6	$	111
Vested and expected to vest after March 31, 2023		2,631,002		$	2.83	6.6	$	183

There were no options granted during the three months ended March 31, 2023. The weighted-average grant-date fair value of options granted during the three months ended March 31, 2022 was $5.72 per share.

The following table summarizes the non-vested stock options that were outstanding as of March 31, 2023 and December 31, 2022:

	Number of Shares		Weighted Average Grant Date Fair Value
Non-vested Options, December 31, 2022		1,118,088	$	6.23
Non-vested Options, March 31, 2023		1,024,318	$	6.13

The total fair value of shares vested during the three months ended March 31, 2023 and 2022 was $0.7 million in each period.

Certain stock option grants under the 2017 Stock Incentive Plan (the “2017 Plan”) allow the recipient to exercise the options prior to the options becoming fully vested. Under the 2017 Plan, the Company retains the right to repurchase shares of its common shares that have been issued upon early exercise of options at the original issue price. During the three months ended March 31, 2023, the

Company did not repurchase any shares. There was no material number of shares of common stock subject to repurchase as of March 31, 2023. Cash received for the early exercise of unvested stock options is initially recorded as a liability and released to equity over the vesting period. There were no early exercised stock options during the three months ended March, 2023. During the three months ended March 31, 2022, early exercised stock options vested were immaterial.

The following table summarizes RSU activity under the Company's incentive plans:

	Number of Shares			Weighted Average Grant Date Fair Value
RSUs outstanding, December 31, 2022		2,858,649		$	4.49
Granted		2,988,302		$	1.65
Vested		(216,253	)	$	5.67
Forfeited		(32,169	)	$	5.28
RSUs outstanding, March 31, 2023		5,598,529		$	2.93