Our share-based compensation consists of stock options, restricted stock units (“RSU”), and performance stock units (“PSU”), and is used to compensate certain employees and non-employee directors. We also offer an employee stock purchase plan to eligible employees.

As of March 31, 2025, there were 12.6 million stock options, RSUs, and PSUs outstanding and 6.6 million shares available for grant under approved equity compensation plans.

Total share-based compensation expense was $45.9 million and $38.0 million for the three months ended March 31, 2025, and 2024, respectively. As of March 31, 2025, there was $310.7 million of share-based compensation expense related to unvested share-based equity awards not yet recognized, which is expected to be recognized over a weighted average period of 2.2 years.

Performance-based stock option activity was as follows:


	Shares		Weighted Average Exercise Price (per share)		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2024		1,729,781	$	65.26		5.4	$	12.8
Granted		—		—		—		—
Exercised		—		—		—		—
Forfeited or expired		—		—		—		—
Outstanding at March 31, 2025		1,729,781	$	65.26		5.1	$	—
Exercisable at March 31, 2025		979,781	$	65.26		5.1	$	—

PSU activity was as follows:


	Shares
Outstanding at December 31, 2024		1,091,885
Granted		576,401
Vested and released		(451,070	)
Forfeited or canceled		(75,664	)
Outstanding at March 31, 2025		1,141,552
Releasable at March 31, 2025		—

Term-based stock option activity was as follows:


	Shares			Weighted Average Exercise Price (per share)			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2024		4,477,645		$	56.53			4.7	$	79.7
Granted		—			—			—		—
Exercised		(19,378	)		(41.64	)		—		—
Forfeited or expired		(3,375	)		(68.46	)		—		—
Outstanding at March 31, 2025		4,454,892		$	56.59			4.5	$	32.7
Exercisable at March 31, 2025		4,374,166		$	56.03			4.5	$	32.7

For most term-based stock options, we estimated an expected term of 7.0 years, based on the vesting period and contractual life.

RSU activity was as follows:


	Shares
Outstanding at December 31, 2024		4,110,131
Granted		2,493,697
Vested and released		(1,246,400	)
Forfeited or canceled		(70,901	)
Outstanding at March 31, 2025		5,286,527
Releasable at March 31, 2025		—

A total of 1.1 million shares of common stock were available for future issuances under the plan as of March 31, 2025.