9. Stock-based compensation

2018 Equity incentive plan

The Company’s 2018 Equity Incentive Plan (the 2018 Plan) allows the Company to issue restricted stock awards and restricted stock units, and to grant incentive stock options or non-qualified stock options. Incentive stock options may be granted only to the Company’s employees including officers and members of the Board who are also employees. Restricted stock awards, restricted stock units and non-qualified stock options may be granted to employees, members of the Board, outside advisors, and consultants of the Company (the Participants). The Company is authorized to issue awards for 4,913,665 shares of Common Stock under the 2018 Plan. The Company has granted awards of common stock in the form of 4,279,693 shares as of December 31, 2021 with none remaining available for future grant. Following the Company’s IPO in October 2020, all remaining shares from the 2018 Plan will be available for issuance under the 2020 Plan (as defined below).

2020 Incentive award plan

The Company adopted the 2020 Incentive Award Plan (the 2020 Plan) effective October 15, 2020. The 2020 Plan provides for a variety of stock-based compensation awards, including stock options, stock appreciation rights, or SARs, restricted stock awards, restricted stock unit awards, performance bonus awards, performance stock unit awards, dividend equivalents, or other stock or cash based awards. The Company has granted 3,867,000 shares subject to awards as of December 31, 2021 with 2,637,000 remaining available for future grant.

Following the effectiveness of the 2020 Plan, the Company will not make any further grants under the 2018 Plan. However, the 2018 Plan will continue to govern the terms and conditions of the outstanding awards granted under this plan. Shares of common stock subject to awards granted under the 2018 Plan that are forfeited or lapse unexercised and which following the effective date of the 2020 Plan are not issued under the 2018 Plan will be available for issuance under the 2020 Plan.

2020 Employee stock purchase plan

The Company adopted the 2020 Employee Stock Purchase Plan (the 2020 ESPP) effective on October 15, 2020. The 2020 ESPP enables eligible employees of the Company to purchase shares of common stock at a discount

to fair market value. The Company has initially reserved for issuance 368,901 shares of common stock pursuant to the 2020 ESPP. As of December 31, 2021, 45,610 grants of awards under this plan have been made.

During the year ended December 31, 2021, the Company's 2020 ESPP compensation expense was $0.9 million. The first purchase in connection with our employee stock purchase plan was in 2021, therefore there was no expense in 2020. The assumptions that the Company used to determine the grant-date fair value of shares granted to participants were as follows, disclosed on a grant date basis:

Stock options

The exercise price for incentive stock options is at least 100% of the fair market value on the date of grant for stockholders owning less than 10% of the voting power of all classes of stock, or at least 110% of the fair market value for stockholders owning more than 10% of the voting power of all classes of stock. Options generally expire in 10 years and vest over periods determined by the Board, generally 48 months. Certain stock options referred to as “early exercise stock options” permit the holders to exercise the option in whole or in part prior to the full vesting of the option in exchange for unvested shares of Restricted Stock with respect to any unvested portion of the option so exercised.

During the years ended December 31, 2021 and December 31, 2020, the Company’s stock option compensation expense was approximately $12.2 million and $2.6 million, respectively, and there was no recognized tax benefit in either year. As of December 31, 2021, the unamortized expense balance was $33.6 million, to be amortized over a weighted-average period of 2.56 years.

The weighted-average grant date fair value of stock options granted was $13.76 per share during the year ended December 31, 2021. The weighted-average grant date fair value of stock options granted was $7.50 per share during the year ended December 31, 2020.

During the year ended December 31, 2021 the Company did not issue shares for unvested stock options, and in the year ended December 31, 2020, the Company issued 371,939 shares of Common Stock upon the exercise of unvested stock options or purchases for unvested restricted stock awards. As of December 31, 2021 and 2020, there were 163,855 and 396,522 shares of Common Stock, respectively, held by employees subject to repurchase at an aggregate price of $0.3 million and $0.6 million, respectively. A corresponding liability was recorded and included in accrued expenses on the consolidated balance sheet as of December 31, 2021 and 2020.

Restricted stock awards

The Company may grant restricted stock purchase awards to the Participants to purchase restricted stock under the Company’s Plan, which are subject to vesting conditions. The purchase prices of the restricted stock are determined by the Board. The Company has a right to repurchase the shares if the Participant’s service period is not fulfilled or upon termination of service at the original per share issuance price. The right of repurchase lapses over a service period which is typically four years with 25% vesting on the first anniversary of the vesting commencement date and 1/48 each month thereafter.

Before the adoption of the Company’s Plan, the Company granted 502,964 restricted stock awards to employees and founders. These restricted stock awards have similar characteristics to the restricted stock awards granted under the Company’s Plan, other than the right of repurchase, which typically lapses over three years with 33% vesting on the first anniversary of the vesting commencement date and 1/36 each month thereafter.

During the years ended December 31, 2021 and December 31, 2020, the Company recorded a total stock-based compensation expense of $357,000 and $361,000, respectively, related to the restricted stock awards. As of December 31, 2021, unrecognized stock-based compensation costs related to outstanding unvested restricted stock awards that are expected to vest were approximately $95,000, expected to be recognized over a weighted-average period of 0.3 years.