13.         Stock-based Compensation

Shares available to grant

On June 8, 2023, the Company held its 2023 Annual Meeting of Stockholders and ratified an amendment to the Company's Amended and Restated 2014 Equity Incentive Plan to increase the total number of shares of common stock authorized for issuance by 1,200 shares. As of June 30, 2023, the total number of shares authorized for grant under the Company's Amended and Restated 2014 Equity Incentive Plan was 3,724, of which 410 were available for future grants.

Stock Options

The following table summarizes information about the Company’s stock options outstanding as of June 30, 2023, and activity during the six months then ended:

As of June 30, 2023, total unrecognized compensation cost related to unvested stock options was $21. This amount is expected to be recognized as stock-based compensation expense in the Company’s condensed consolidated statements of operations and comprehensive loss over the remaining weighted average vesting period of 0.39 years.

There were no stock options awarded during the three and six months ended June 30, 2023 and 2022.

Restricted Stock Units

The Company issues time-based restricted stock units (“RSUs”) and performance-based restricted stock units ("PSUs") to employees and non-employee members of the Board. Each RSU and PSU represents the right to receive one share of the Company’s common stock upon vesting and subsequent settlement. PSUs vest upon achievement of performance targets based on the Company's annual operating plan.

The fair values of RSUs and PSUs are determined based on the closing price of the Company’s common stock on the date of grant.

Combined RSU and PSU activity for the six months ended June 30, 2023 is summarized below:

As of June 30, 2023, $2,174 of total unrecognized compensation expense related to unvested RSUs and PSUs was expected to be recognized over a weighted average period of 1.55 years.

Compensation Expense

Total stock-based compensation expense related to options, RSUs and PSUs granted to employees and non-employee members of the board of directors is included in the condensed consolidated statements of operations and comprehensive loss as follows:

401(k) Plan Share Match

During the six months ended June 30, 2023 and 2022, the Company issued 161 and 68 shares of common stock with a fair value of $249 and $176, to eligible employees’ deferral accounts for the 401(k) Plan matching contribution representing 50% of each eligible employee’s elected deferral (up to the statutory limit) for the years ended December 31, 2022 and 2021, respectively. 

The expense for the 401(k) plan share matching was $219 and $103 for the six months ended June 30, 2023 and 2022, respectively.