The Company adopted a stock plan in 2006 (the "2006 Plan"), which provided for the granting of incentive stock options, non-qualified stock options, stock appreciation rights, deferred stock awards, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights. In October 2014, the 2006 Plan was terminated, and the Company adopted a new plan (the "2014 Plan"). No further grants or awards were subsequently made under the 2006 Plan. A total of 3,662 options were awarded from the 2006 Plan and as of December 31, 2023, 79 of these options remain outstanding and eligible for future exercise.

The 2014 Plan provides for the granting of incentive stock options, non-qualified stock options, stock appreciation rights, deferred stock awards, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights. In May 2018, the 2014 Plan was terminated, and the Company adopted a new 2018 Stock Option and Incentive Plan, which was amended in May 2020 (the "2018 Stock Plan"). A total of 16,896 options were awarded from the 2014 Plan and as of December 31, 2023, 14,065 of these options remain outstanding and eligible for future exercise. A total of 3,619 restricted stock awards were awarded from the 2014 Plan and as of December 31, 2023, all of these restricted stock awards have vested. No further stock awards may be issued from the 2014 Plan.

The 2018 Stock Plan initially reserved for issuance 32,500 shares of the Company's common stock for grants of incentive stock options, non-qualified stock options, stock grants and other stock-based awards. In accordance with the terms of the 2018 Stock Plan, beginning on the first day in January 2019, the Company's Board of Directors has annually approved the addition of shares to the 2018 Stock Plan in amounts equal to 5% of the outstanding shares of the Company's common stock on the day prior to the increase. Effective January 1, 2024 and January 1, 2023, Yield10's Board of Directors approved the addition of 601,621 and 247,210 shares, respectively. As of December 31, 2023, a total of 1,517,319 options and restricted stock awards have been issued from the 2018 Stock Plan, and as of that date, 1,324,777 options and restricted stock awards remain outstanding.

The Company recognized stock-based compensation expense, related to employee stock awards, including awards to non-employees and members of the Board of Directors, of $1,592 and $1,903 for the years ended December 31, 2023 and 2022, respectively. At December 31, 2023, there was approximately $2,091 of stock-based compensation expense related to unvested awards not yet recognized which is expected to be recognized over a weighted average period of 2.52 years.

Options granted under the 2006 Plan, 2014 Plan and 2018 Stock Plan generally vest ratably over periods of one to four years from the date of hire for new employees, the date of award for existing employees, or date of commencement of services with the Company for non-employees, and generally expire ten years from the date of issuance. The Company's policy is to issue new shares upon the exercise of stock options.


	Number of Shares	Weighted Average Exercise Price		Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Balance at December 31, 2021	722,765	$	19.22	8.79	$	—
Granted	260,285	3.72
Exercised	—	—
Forfeited	(1,859)	7.55
Expired	(1,443)	712.92
Balance at December 31, 2022	979,748	14.10		8.15	$	—
Granted	457,600	2.16
Exercised	—	—
Forfeited	(66,423)	6.35
Expired	(32,004)	75.42
Balance at December 31, 2023	1,338,921	$	8.94	7.46	$	—
Vested and expected to vest at December 31, 2023	1,338,921	$	8.94	7.46	$	—
Exercisable at December 31, 2023	664,919	$	14.15	6.81	$	—

The weighted average grant date fair value per share of options granted during fiscal years 2023 and 2022, was $1.63 and $3.31, respectively. No options were exercised during 2023 and 2022, and therefore the intrinsic value for exercised options during the two years was not applicable. The weighted average remaining contractual term for options outstanding as of December 31, 2023 was 7.46 years.

For the years ended December 31, 2023, and 2022, the Company determined the fair value of stock options using the Black-Scholes option-pricing model with the following assumptions for option grants, respectively:


	Year Ended December 31,
	2023	2022
Expected dividend yield	—	—
Risk-free rate	3.5% - 4.7%	1.6% - 4.3%
Expected option term (in years)	6.2 - 6.3	6.2 - 10.0
Volatility	119% - 123%	116% - 126%

The Company determined its volatility assumption based on actual market price fluctuations experienced during its trading history. The risk-free interest rate used for each grant is equal to the U.S. Treasury yield curve in effect at the time of grant for instruments with a term similar to the expected life of the related option. The expected term of the options is based upon evaluation of historical and expected future exercise behavior.

The stock price volatility and expected terms utilized in the calculation involve management's best estimates at that time, both of which impact the fair value of the option calculated under the Black-Scholes methodology and, ultimately, the expense that will be recognized over the life of the option. The accounting standard for stock-based compensation requires that the Company recognize compensation expense for only the portion of options that vest. The Company recognizes stock option forfeitures resulting from award terminations in the period in which the forfeiture occurs.

The Company records stock compensation expense for RSUs on a straight-line basis over their requisite service period, which approximates the vesting period, based on each RSU's award date market value. As RSUs vests, the Company

withholds a number of shares from its employees with an aggregate fair market value equal to the minimum tax withholding amount (unless the employee makes other arrangements for payment of the tax withholding) from the common stock issuable at the vest date. The Company then pays the minimum required income tax for the employees. During the years ended December 31, 2023 and December 31, 2022, the Company withheld vested shares with a fair value of $41 and $37, respectively, to pay for minimum tax withholding associated with RSU vesting.


	Number of RSUs	Weighted Average Remaining Contractual Life (years)
Outstanding at December 31, 2022	27,123
Awarded	—
Released	(27,123)
Forfeited	—
Outstanding at December 31, 2023	—	0.00

Weighted average remaining recognition period (years)	0.00

Subsequent to year-end, on February 15, 2024, the Company's Board of Directors awarded 600,000 RSUs to certain officers, senior staff and outside consultants. These RSUs will vest in 50% increments 6 and 12 months from the date the awards were granted.