We issue incentive and non-qualified stock options, restricted stock units, and restricted stock awards to employees and non-employees with vesting requirements varying from six months to four years. We utilize the Black-Scholes valuation model for valuing stock option issuances and the grant date fair value for valuing restricted stock issuances.

Equity based compensation expense, including vesting of restricted stock units, totaled $6,933,718 and $10,309,535 for the years ended December 31, 2023 and 2022, respectively. Equity based compensation expense is recorded within personnel on the consolidated statements of operations and comprehensive income (loss).

We adopted the 2016 Employee Stock Option Plan on January 16, 2016. The number of awards authorized for issuance under the plan was 263,158. We had 61,292 and 77,529 options issued and outstanding under the plan as of December 31, 2023 and 2022, respectively. We had no restricted stock awards issued and outstanding as of December 31, 2023 and 2022. During the years ended December 31, 2023 and 2022, 16,768 and 69,968 options were exercised into 16,343 and 69,304 shares of common stock, respectively. The differences between options exercised and common stock issued are due to shares withheld to cover exercise costs.

We adopted the 2019 Equity Incentive Plan on June 25, 2019. The number of awards authorized for issuance under the plan was 684,211. We had 186,739 and 212,958 options issued and outstanding as of December 31, 2023 and 2022, respectively. We had no restricted stock units issued and outstanding as of December 31, 2023, and 5,280 restricted stock units issued and outstanding as of December 31, 2022. During the year ended December 31, 2023, no options were exercised. During the year ended December 31, 2022, 12,041 options were exercised into 10,420 shares of common stock. The differences between options exercised and common stock issued are due to shares withheld to cover exercise costs.

We adopted the 2021 Equity Incentive Plan on June 15, 2021. The number of awards originally authorized for issuance under the plan is 1,092,013. As of December 31, 2023 and 2022, we had 5,675 and 6,163 options issued and outstanding, respectively. We had 353,971 and 337,660 restricted stock units issued and outstanding as of December 31, 2023 and 2022, respectively. During the years ended December 31, 2023 and 2022, no options issued under this plan were exercised into shares of common stock.

The following tables summarize the options issued, outstanding, and exercisable under our equity based compensation plans as of December 31, 2023 and 2022:


	For the year ended December 31, 2023
	Number of Options*	Weighted Average Exercise Price*		Intrinsic Value		Weighted Average Remaining Life
Outstanding, beginning of year	296,650	$	59.28	$	686,035	6.14
Granted	—	—		—		—
Exercised	(16,343)	1.90		203,269		—
Canceled	(26,601)	72.85		—		—
Outstanding, end of year	253,706	62.01		1,146,614		5.85
Exercisable, end of year	232,041	56.42		1,139,545		5.72
Expected to vest, end of year	21,665	$	121.85	$	7,069	7.30


	For the year ended December 31, 2022
	Number of Options*	Weighted Average Exercise Price*		Intrinsic Value		Weighted Average Remaining Life
Outstanding, beginning of year	557,785	$	66.12	$	23,079,520	7.76
Granted	10,405	27.74		—		—
Exercised	(79,724)	6.08		2,383,405		—
Canceled	(191,816)	98.42		—		—
Outstanding, end of year	296,650	59.28		686,035		6.14
Exercisable, end of year	254,118	49.40		685,914		5.89
Expected to vest, end of year	42,532	$	117.80	$	121	7.61

The following table represents the assumptions used for estimating the fair values of stock options granted to our employees, contractors, and non-employees under the Black-Scholes valuation model. The risk-free interest rate is based on the U.S. Treasury yield curve in effect on the grant date:


	2023		2022
Risk-free interest rate	0.00%–0.00%		3.46%–3.91%
Expected volatility	0.00%–0.00%		115.75%–116.01%
Expected life (in years)	0.00		6.00
Weighted average estimated fair value of options granted	$	—	$	27.74

Restricted stock award and restricted stock unit transactions during the years ended December 31, 2023 and 2022 are summarized as follows:


	For the year ended December 31, 2023			For the year ended December 31, 2022
	Number of Shares*	Weighted Average Grant Date Fair Value*		Number of Shares*	Weighted Average Grant Date Fair Value*
Unvested shares, beginning of year	342,940	$	30.02	153,242	$	160.36
Granted	356,679	18.00		400,363	22.42
Vested	(293,878)	25.09		(36,537)	144.78
Forfeited or surrendered	(49,138)	35.35		(174,128)	104.12
Unvested shares, end of year	356,603	$	21.32	342,940	$	30.02

During the year ended December 31, 2023, employees and non-employees received restricted stock units totaling 354,047 and restricted stock awards totaling 2,632. Vesting of restricted stock units totaled 293,878. The shares underlying the restricted stock units granted in 2023 were assigned a weighted average fair value of $18.00 per share, for a total value of $6,420,222. The restricted stock issuances are scheduled to vest over a range of one to four years.

During the year ended December 31, 2022, employees and non-employees received restricted stock units totaling 400,363. Vesting of restricted stock units and restricted stock awards totaled 35,513 and 1,024, respectively. The shares underlying the restricted stock units granted in 2022 were assigned a weighted average fair value of $22.42 per share, for a total value of $8,976,136. The restricted stock issuances are scheduled to vest over a range of one to four years.

As of December 31, 2023, the total compensation cost related to non-vested awards not yet recognized is $7,508,560 and is expected to be recognized over the weighted average remaining recognition period of approximately 2.5 years.

As of December 31, 2022, the total compensation cost related to non-vested awards not yet recognized is $9,984,655 and is expected to be recognized over the weighted average remaining recognition period of approximately 2.0 years.