
	Year Ended December 31,
(In thousands)	2023		2022		2021
Research and development	$	97,273	$	92,161	$	68,415
Selling, general and administrative	124,407		138,488		97,302
Total	$	221,680	$	230,649	$	165,717


	Year Ended December 31,
(In thousands)	2023		2022		2021

Time-based restricted stock units	$	55,169	$	12,791	$	4,231
Performance-based restricted stock units	63,879		102,925		39,943
Time-based stock options	99,165		114,901		118,635
Other equity programs	7,652		4,057		6,235
Less: Stock-based compensation expense capitalized to inventory	(4,185)		(4,025)		(3,327)
Total	$	221,680	$	230,649	$	165,717

The following table summarizes our unrecognized stock-based compensation expense, net of estimated forfeitures, by type of awards, and the weighted-average period over which that expense is expected to be recognized:


	As of December 31, 2023
	Unrecognized Expense, Net of Estimated Forfeitures (in thousands)		Weighted-average Recognition Period (in years)
Type of award:
Time-based restricted stock units	$	125,118	2.14
Performance-based restricted stock units *	$	1,792	0.13
Time-based stock options	$	124,825	2.04
Other equity programs	$	3,306	0.55


	Number of Units (in thousands)	Weighted-average Grant Date Fair Value (per share)
Outstanding as of December 31, 2022	292	$	165.27
Awarded	922	$	188.78
Released	(126)	$	164.47
Cancelled	(63)	$	186.25
Outstanding as of December 31, 2023	1,025	$	185.24


	Number of Units (in thousands)	Weighted-average Grant Date Fair Value (per share)
Outstanding as of December 31, 2022	1,195	$	144.77
Awarded	439	$	190.01
Released	(472)	$	139.38
Cancelled	(129)	$	150.02
Outstanding as of December 31, 2023	1,033	$	165.82

The performance-based restricted stock units granted in 2023 and 2022 will vest upon the later of the one-year anniversary of the date of grant and the achievement of specific clinical development, regulatory, commercial and/or financial performance events, as approved by our people, culture and compensation committee.


	Number of Options (in thousands)	Weighted-average Exercise Price (per share)		Weighted-average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	7,868	$	120.59
Granted	412	$	192.68
Exercised	(1,068)	$	99.43
Cancelled	(252)	$	148.27
Outstanding as of December 31, 2023	6,960	$	127.11	5.96	$	451,402
Exercisable as of December 31, 2023	5,042	$	114.14	5.21	$	390,672
Vested or expected to vest as of December 31, 2023	6,803	$	126.23	5.90	$	447,000

The weighted-average fair value of stock options granted was $96.53, $80.65 and $82.59 per share for the years ended December 31, 2023, 2022 and 2021, respectively. The intrinsic value of stock options exercised was $107.0 million, $289.3 million and $247.8 million for the years ended December 31, 2023, 2022 and 2021, respectively. We satisfy stock option exercises with newly issued shares of our common stock.


	Number of Options (in thousands)	Weighted-average Exercise Price (per share)		Weighted-average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	556	$	97.28
Granted	—	$	—
Exercised	(94)	$	88.01
Cancelled	—	$	—
Outstanding as of December 31, 2023	462	$	99.16	3.04	$	42,632
Exercisable as of December 31, 2023	462	$	99.16	3.04	$	42,632

During the years ended December 31, 2023, 2022 and 2021, there were 0, 0 and 197,102 performance-based stock options that vested, respectively. The intrinsic value of performance-based stock options exercised was $9.7 million, $74.4 million and $40.2 million for the years ended December 31, 2023, 2022 and 2021, respectively. We satisfy performance-based stock option exercises with newly issued shares of our common stock.

The fair value of stock options, at date of grant, based on the following assumptions, was estimated using the Black-Scholes option-pricing model. Our expected stock-price volatility assumption is based on the historical volatility of our publicly traded stock. The expected life assumption is based on our historical data. The dividend yield assumption is based on the fact that we have never paid cash dividends and have no present intention to pay cash dividends. The risk-free interest rate used for each grant is equal to the zero coupon rate for instruments with a similar expected life.


	Year Ended December 31,
	2023	2022	2021
Risk-free interest rate	3.5 - 4.1%	1.3 - 4.2%	0.4 - 1.4%
Expected dividend yield	—	—	—
Expected option life	5.1 - 7.0 years	5.1 - 7.0 years	5.4 - 6.8 years
Expected volatility	49 - 60%	50 - 60%	58 - 63%

In May 2022, our stockholders approved the amendment and restatement of our 2018 Stock Incentive Plan, as amended, or the Amended and Restated 2018 Plan, which increased the number of shares authorized for issuance thereunder by 6,000,000 shares. The Amended and Restated 2018 Plan provides for the granting of stock options, restricted stock and restricted stock units (together, restricted stock awards), stock appreciation rights and other stock-based awards, and has a fungible share pool. Any award that is not a full value award is counted against the authorized share limits specified as one share for each share of common stock subject to the award, and all full value awards, defined as restricted stock awards or other stock-based awards, are counted as one and a half shares for each one share of common stock subject to such full value award.

As of December 31, 2023, an aggregate of 18,256,842 shares of common stock were reserved for issuance under our stock plans, including outstanding stock options to purchase 7,422,183 shares of common stock, 2,057,874 outstanding restricted stock units, 8,168,918 of common stock available for additional equity awards and 607,867 shares available for future grant under our Amended and Restated 2004 Employee Stock Purchase Plan, as amended, or the Amended and Restated ESPP. Each stock option shall expire within 10 years of issuance. Time-based stock options granted to employees generally vest as to 25% of the shares on the first anniversary of the grant date and 6.25% of the shares at the end of each successive three-month period thereafter until fully vested. Restricted stock units granted to employees generally vest over a three-year period, with one-third of the shares vesting on each of the three successive anniversaries of the grant date.

In 2004, we adopted the 2004 Employee Stock Purchase Plan and in 2017, our stockholders approved the Amended and Restated ESPP. In 2020, our stockholders approved an amendment to the Amended and Restated ESPP, to increase the number of shares authorized for issuance to 1,965,789 shares. Under the Amended and Restated ESPP, as amended, each offering

period is six months, at the end of which employees may purchase shares of common stock through payroll deductions made over the term of the offering. The per-share purchase price at the end of each offering period is equal to the lesser of 85% of the closing price of our common stock at the beginning or end of the offering period. We issued 108,905 and 119,285 shares during the years ended December 31, 2023 and 2022, respectively.

We estimate the fair value of shares to be issued under the Amended and Restated ESPP, as amended, using the Black-Scholes option-pricing model on the date of grant, or first day of the offering period, using the same methodology approach as the employee stock option grants. The following table summarizes the Black-Scholes valuation assumption inputs for stock purchase rights granted under the employee stock purchase plan:


	Year Ended December 31,
	2023	2022	2021
Risk-free interest rate	5.1% - 5.4%	1.4% - 4.5%	0.03% - 0.06%
Expected dividend yield	—	—	—
Expected option life	6 months	6 months	6 months
Expected volatility	34% - 39%	53% - 71%	41% - 46%

We have authorized up to 5,000,000 shares of preferred stock, $0.01 par value per share, for issuance. The preferred stock will have such rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, as shall be determined by our board of directors upon its issuance. As of December 31, 2023 and 2022, there were no shares of preferred stock outstanding.