Note 7. Stock-Based Compensation

Total non-cash stock-based compensation expense recorded related to common stock awards, stock options, RSAs and PSAs for the three and six months ended June 30, 2026 and 2025 is as follows (in millions): 

The total stock-based compensation expense recorded in R&D and general and administrative expenses in the Company’s consolidated statements of operations for the three and six months ended June 30, 2026 and 2025 is as follows (in millions):

2020 Omnibus Incentive Plan

The Company maintains the 2020 Omnibus Incentive Plan (the 2020 Plan), under which eligible participants may be awarded various types of stock-based compensation, including stock options, restricted stock awards, and other stock-based and cash-based awards. As of June 30, 2026, there were 1,300,299 shares of common stock reserved and available for issuance under the 2020 Plan.

Restricted Stock Awards

The following summarizes the Company’s RSA activity (limited to RSAs with no performance-based conditions) for the six months ended June 30, 2026:

During the six months ended June 30, 2026, the Company granted 53,155 RSAs to the independent members of its Board of Directors (the Board) and 16,000 RSAs to an external consultant. These awards vest in four equal installments at the end of each calendar quarter of 2026. During the six months ended June 30, 2026, the Company also granted 44,833 RSAs to new employees. These awards vest in three equal installments on each of the first three anniversaries of the grant date.

The weighted-average grant-date fair value per share of RSAs granted for the six months ended June 30, 2026 and 2025 was $13.12 and $8.63, respectively. During the six months ended June 30, 2026, a total of 51,276 RSAs vested, with an aggregate fair value of $0.6 million, and the Company withheld 2,848 shares to satisfy tax obligations, resulting in 48,428 net shares issued. During the six months ended June 30, 2025, 122,283 RSAs with an aggregate fair value of $1.0 million vested, and the Company withheld 29,440 shares to satisfy tax obligations, resulting in 92,843 net shares issued.

During the three months ended June 30, 2026 and 2025, the Company recognized approximately $1.3 million and $0.4 million in total stock-based compensation expense from RSAs, respectively. During the six months ended June 30, 2026 and 2025, the Company recognized approximately $2.6 million and $1.7 million in total stock-based compensation expense from RSAs, respectively. The stock-based compensation expense recorded during the six months ended June 30, 2025 included approximately $0.5 million of stock-based compensation expense related to accelerated vesting in connection with a separation agreement with a former employee. As of June 30, 2026, total unrecognized compensation cost related to RSAs was $8.8 million, which is expected to be recognized over a remaining weighted-average vesting period of 2.04 years.

Performance-based Restricted Stock Awards

The following summarizes the Company’s PSA activity for the six months ended June 30, 2026:

The weighted-average grant-date fair value per share of PSAs granted for the six months ended June 30, 2026 and 2025 was $11.80 and $6.99, respectively. During the six months ended June 30, 2026, a total of 100,001 PSAs vested, with an aggregate fair value of $1.1 million, and the Company withheld 41,559 shares to satisfy tax obligations, resulting in 58,442 net shares issued.

For the three months ended June 30, 2026, the Company recognized an immaterial amount of stock-based compensation expense from PSAs. For the three months ended June 30, 2025, the Company recognized approximately $0.2 million in stock-based compensation expense from PSAs. For the six months ended June 30, 2026 and 2025, the Company recognized approximately $1.1 million and $0.2 million in stock-based compensation expense from PSAs, respectively. As of June 30, 2026, total unrecognized compensation cost related to PSAs was $4.1 million, which is expected to be recognized over a remaining weighted-average vesting period of 1.48 years.

As of June 30, 2026, the Company had 1,013,738 PSAs outstanding with three specific R&D fuel program milestones and one specific financial milestone (the Tranche-based PSAs). During the six months ended June 30, 2026, 167,512 shares of Tranche-based PSAs were granted to new employees. Each milestone applies only to a separate portion of the Tranche-based PSAs. Vesting of the Tranche-based PSAs occurs in unequal tranches depending on which milestone is certified and is subject to the grantee having completed at least twelve months of continuous service with the Company as of the milestone achievement date. The performance period for achieving these milestones extends from the grant date to December 31, 2028. As of June 30, 2026, management concluded that only one performance milestone was probable of achievement.

During the three-months ended June 30, 2026, management concluded a performance milestone previously deemed probable was no longer probable based on revised expectations during the quarter. As a result, the Company reversed $0.7 million of previously recorded stock-based compensation related to this performance milestone. During the three and six months ended June 30, 2026, the Company recognized net stock-based compensation expense of $(0.2) million and $0.6 million, respectively, related to the Tranche-based PSAs. These amounts include the reversal of $0.7 million of previously recognized stock-based compensation related to the performance milestone. No stock-based compensation expense related to the Tranche-based PSAs was recorded during the six months ended June 30, 2025.

As of June 30, 2026, the Company had 199,999 PSAs outstanding, which were granted in April 2025 (the April 2025 PSAs) with a performance condition requiring the successful insertion of the Company’s fuel material coupon samples into the Advanced Test Reactor at INL by December 31, 2026. This condition was satisfied in November 2025 and satisfaction was subsequently certified by the Compensation Committee. The April 2025 PSAs are also subject to the participant’s continuous service over a three-year period from the grant date. During the three months ended June 30, 2026 and 2025, the Company recognized $0.2 million and $0.2 million in stock-based compensation expense related to the April 2025 PSAs. During the six months ended June 30, 2026 and 2025, the Company recognized $0.5 million and $0.2 million in stock-based compensation expense related to the April 2025 PSAs.