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Equity-Based Compensation (Tables)
6 Months Ended
Jun. 30, 2021
Share-based Payment Arrangement [Abstract]  
Equity-Based Compensation Expense Classification in Statement of Operations
Equity-based compensation expense is classified in the statements of operations as follows:
Three Months Ended
June 30,
Six Months Ended
June 30,
2021202020212020
Research and development expense$361 $203 $618 $360 
General and administrative expense403 341 663 625 
$764 $544 $1,281 $985 
Assumptions Used to Determine Fair Value of Common Stock Option Grants In addition to an assumption on the expected term of the option grants as discussed below, application of the Black-Scholes model requires additional inputs for which we have assumed the values described in the table below:
Six Months Ended
June 30,
20212020
Expected term
5.0 to 6.1 years
5.2 to 6.1 years
Risk-free interest rate
0.36% to 1.12%; weighted avg. 1.05%
0.41% to 1.68%; weighted avg. 0.67%
Expected volatility
81.7% to 83.6%; weighted avg. 82.6%
81.0% to 85.8%; weighted avg. 83.8%
Forfeiture rate%%
Expected dividend yield— %— %
The fair value of the underlying common stock and the exercise price for the common stock options granted during the six months ended June 30, 2021 and 2020 are summarized in the table below:
Common Stock Options Granted During Period Ended:Fair Value of Underlying Common StockExercise Price of Common Stock Option
Six months ended June 30, 2021
$1.54 to $2.57; weighted avg. $1.88
$1.54 to $2.57; weighted avg. $1.88
Six months ended June 30, 2020
$1.19 to $2.80:
weighted avg. $1.85
$1.19 to $2.80:
weighted avg. $1.85
Common Stock Option Activity
A summary of common stock option activity as of the periods indicated is as follows:
OptionsWeighted-Average Exercise PriceWeighted-Average Remaining Contractual Term (years)Aggregate Intrinsic Value (thousands)
Outstanding - December 31, 20207,227,296 $2.24 6.8$1,719 
Granted4,270,086 1.88 
Exercised(342,246)1.60 
Forfeited(95,702)2.27 
Outstanding - June 30, 202111,059,434 $2.12 7.8$1,019 
Exercisable - June 30, 20214,580,439 $2.29 5.5$832 
Vested and Expected to Vest -
June 30, 2021
10,559,034 $2.13 7.7$1,007 
Restricted Stock Unit Awards Activity
A summary of restricted stock unit activity of the periods indicated is as follows:
Restricted Stock UnitsWeighted-Average Grant Date Fair Value
Unvested balance - December 31, 2020— $— 
Granted286,000 1.90 
Unvested balance - June 30, 2021286,000 $1.90