The following table summarizes the Company’s stock awards granted for each of the periods indicated:


	For the Three Months Ended June 30,								For the Six Months Ended June 30,
	2022				2021				2022				2021
	Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value
Stock options		207,583	$	43.40		72,110	$	39.79		1,499,120	$	46.49		1,431,747	$	48.87
Restricted stock units*		147,075	$	72.99		37,240	$	75.30		859,510	$	78.78		726,607	$	86.53

*Included in 2022 RSUs are 38,500 shares with performance conditions which are related to regulatory approval of certain of the Company's product candidates. As of June 30, 2022, none of the performance conditions are probable of being achieved. If the performance milestones are achieved within the required time frame, the Company may recognize up to $3.1 million of stock-based compensation related to these grants. Stock options and the remaining RSUs granted during the periods presented in the table have only service-based criteria and vest over four years.

In June 2017, the Company granted its Chief Executive Officer 3,300,000 options with service and market conditions which were subject to a five-year cliff vesting schedule. On April 19, 2022 (the “Effective Date”), the Company entered into an agreement with its Chief Executive Officer to modify the vesting conditions of the options. Under the agreement, one-third of the options vested (the “Vested Tranche”) on the Effective Date with no required service or market conditions. Subject to the Chief Executive Officer's continued service through each applicable vesting date and the compound annual growth rate of the Company's common stock exceeding that of the Nasdaq Biotech Index in varying percentages, the remaining two-thirds of the options (the “Unvested Tranche”) shall vest in varying increments at any time between the Effective Date and June 26, 2025 (the “Measurement Period”) when (and if) the average of the closing price of the Company’s common stock during any consecutive 20 trading day period during the Measurement Period reaches certain pre-determined target stock prices. Additionally, the Chief Executive Officer is subject to a one-year post-exercise restriction to sell, transfer or dispose shares acquired upon the exercise of any options that vest after deduction of any shares withheld or sold to pay the applicable aggregate exercise price and/or withholding taxes.

To determine the incremental compensation cost of the modification, the fair value of the modified awards was compared to the fair value of the original awards measured immediately before its terms or conditions were modified. As the Vested Tranche became immediately vested on the Effective Date, the Vested Tranche does not have service or market conditions. As such, the post-modification fair value for the Vested Tranche is based on the Black-Scholes-Merton option-pricing model, while the pre-modification fair value is based on a lattice model with Monte Carlo simulations. The incremental compensation cost of $43.9 million was immediately recognized as stock-based compensation expense in the three months ended June 30, 2022.

The Unvested Tranche represents awards with market conditions only. Both the pre- and post-modification fair values for the Unvested Tranche are determined by a lattice model with Monte Carlo simulations. As a result of the modification, the Company is expected to recognize incremental compensation cost of $82.1 million associated with the Unvested Tranche. The incremental costs related to varying increments of the Unvested Tranche will be recognized as stock-based compensation expense over their respective derived service periods, an output from the Monte Carlo simulation, and will be fully recognized over approximately 1.3 years. For the three months ended June 30, 2022, the Company recorded $29.8 million of stock-based compensation expense related to the Unvested Tranche.

For the three months ended June 30, 2022 and 2021, total stock-based compensation expense was $102.9 million and $29.0 million, respectively. For the six months ended June 30, 2022 and 2021, total stock-based compensation expense was $132.1 million and $57.5 million, respectively. The following table summarizes stock-based compensation expense by function included within the unaudited condensed consolidated statements of operations and comprehensive loss:


		For the Three Months Ended June 30,				For the Six Months Ended June 30,
		2022		2021		2022		2021
	(in thousands)
Research and development		$	14,467	$	12,860	$	27,535	$	23,986
Selling, general and administrative			88,425		16,109		104,555		33,491
Total stock-based compensation expense		$	102,892	$	28,969	$	132,090	$	57,477

The following table summarizes stock-based compensation expense by grant type included within the unaudited condensed consolidated statements of operations and comprehensive loss:


		For the Three Months Ended June 30,				For the Six Months Ended June 30,
		2022		2021		2022		2021
	(in thousands)
Stock options		$	89,155	$	17,587	$	105,561	$	34,606
Restricted stock awards/units			12,378		10,573		23,743		20,504
Employee stock purchase plan			1,359		809		2,786		2,367
Total stock-based compensation expense		$	102,892	$	28,969	$	132,090	$	57,477