In 2017, the Company’s board of directors adopted the 2017 Equity Incentive Plan (“2017 Plan”), which was approved by the Company’s stockholders. The 2017 Plan provides for the grant of incentive stock options to the Company’s employees and any parent and subsidiary corporations’ employees, and for the grant of nonstatutory stock options, stock appreciation rights, restricted stock, restricted stock units, performance units, performance shares, other cash-based awards and other stock-based awards to the Company’s employees, directors and consultants and the Company’s parent, subsidiary, and affiliate corporations’ employees and consultants. The 2017 Plan has 14,622,416 authorized shares of the Company’s Class A common stock reserved for issuance.

The following table summarizes the restricted stock units, or RSUs, awarded under the 2017 Plan for the period:

	Number of RSUs
Outstanding as of January 1, 2021		1,154,936
Granted		338,270
Vested		(359,773	)
Forfeited		(69,801	)
Outstanding as of September 30, 2021		1,063,632

The weighted average grant date fair value of the RSUs was $62.92 and the RSUs generally vest in four equal annual installments. Total compensation cost related to nonvested awards not yet recognized as of September 30, 2021, totaled $37.2 million, and is expected to be recognized over a weighted average period of 2.4 years.

The following table summarizes the stock option activity under the 2017 Plan for the period:

	Number of options			Weighted average exercise price per share		Weighted average remaining contractual term (years)		Aggregate intrinsic value (in millions)
Outstanding as of January 1, 2021		4,203,482		$	45.68		9.7
Granted		221,153		$	61.11
Exercised		(20,681	)	$	41.96
Forfeited		(182,471	)	$	47.08
Outstanding as of September 30, 2021		4,221,483		$	46.44		8.9
Exercisable as of September 30, 2021		21,792		$	31.85		8.2	$	0.8

The total intrinsic value of the 2017 Plan stock options exercised during the nine months ended September 30, 2021, was $0.6 million.

The Board of Directors adopted the 2021 Employee Stock Purchase Plan (“ESPP”) on February 16, 2021, which was subsequently approved by our stockholders and became effective on June 2, 2021. The maximum number of shares available for issuance under the ESPP is 3,200,000 shares of the Company’s Class A common stock.

The purchase price for each share of common stock purchased under the ESPP will be 85% of the lower of (a) the fair market value per share on the first day of the applicable offering period or (b) the fair market value per share on the applicable purchase date.

Each offering period will last a number of months determined by the plan administrator, up to a maximum of 27 months. The initial offering period began on July 15, 2021, and will end on January 14, 2022, and new offering periods are expected to begin on each January 15 and July 15 thereafter, unless modified by the plan administrator. The ESPP allows participants to purchase the Company’s common stock through payroll deductions, up to a maximum of 15% of their eligible compensation or $25,000, whichever is lower, and subject to limitations under Section 423 of the Internal Revenue Code. The plan administrator has limited participant contributions to $1,000 per month to prevent prejudicial advantages to higher compensated employees. Participants may withdraw from the ESPP and receive a refund of their accumulated payroll contributions at any time prior to a purchase date.

As of September 30, 2021, $2.1 million has been withheld on behalf of employees for a future purchase under the ESPP due to the timing of payroll deductions. There were no purchases related to the ESPP for the three or nine months ended September 30, 2021. The Company recognized $0.5 million of stock-based compensation expense related to the ESPP for the three and nine months ended September 30, 2021.

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Cost of revenue – maintenance and other services	$	1,411	$	684	$	3,791	$	1,602
Research and development		3,894		2,428		11,223		5,686
Sales and marketing		3,673		1,949		10,800		3,949
General and administrative		1,955		1,173		5,415		2,702
Total stock-based compensation expense	$	10,933	$	6,234	$	31,229	$	13,939