Equity Incentive Plans

We maintain two equity incentive plans: the 2009 Equity Incentive Plan (the 2009 Plan) and the 2015 Equity Incentive Plan (the 2015 Plan). In August 2015, our board of directors adopted, and in September 2015 our stockholders approved, the 2015 Plan, which became effective in connection with our initial public offering (IPO) and serves as the successor to the 2009 Plan. The 2015 Plan provides for grants of incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards, performance cash awards, and other forms of stock awards to our employees, directors and consultants.

The exercise price of stock options will generally not be less than 100% of the fair market value of our common stock on the date of grant, as determined by our board of directors. Our equity awards generally vest over a two to four year period and expire no later than ten years from the date of grant.

2015 Employee Stock Purchase Plan

In August 2015, our board of directors adopted, and our stockholders approved, the 2015 Employee Stock Purchase Plan (2015 ESPP), which became effective in connection with our IPO.

The 2015 ESPP allows eligible employees to purchase shares of our Class A common stock at a discount through payroll deductions of up to 30% of their eligible compensation, subject to a cap of 3,000 shares on any purchase date or $25,000 in any calendar year (as determined under applicable tax rules). The 2015 ESPP provides for 24 month offering periods beginning March 16th and September 16th of each year, and each offering period consists of four six-month purchase periods, subject to a reset provision. If the closing stock price on the offering date of a new offering falls below the closing stock price on the offering date of an ongoing offering, the ongoing offering would terminate immediately following the purchase of ESPP shares on the purchase date immediately preceding the new offering and participants in the terminated ongoing offering would automatically be enrolled in the new offering (ESPP reset), resulting in a modification. On each purchase date, eligible employees will purchase our Class A common stock at a price per share equal to 85% of the lesser of the fair market value of our Class A common stock on (1) the first trading day of the applicable offering period or (2) the purchase date. There was an ESPP reset in the three months ended April 30, 2017 that resulted in a total modification charge of $9.0 million, which is recognized over the new offering period ending March 15, 2019.

We recognized stock-based compensation expense related to our 2015 ESPP of $4.7 million and $11.6 million during the three months ended October 31, 2017 and 2018 and $12.6 million and $26.2 million during the nine months ended October 31, 2017 and 2018. As of October 31, 2018, there was $36.3 million of unrecognized stock-based compensation expense related to our 2015 ESPP, which is expected to be recognized over a weighted-average period of approximately 0.9 years.

Stock Options

A summary of stock option activity under our equity incentive plans and related information is as follows:



	Options Outstanding
	Number of Shares		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (In Years)	Aggregate Intrinsic Value (in thousands)
Balance as of January 31, 2018	46,359,949		$	7.75	6.3	$	574,224
Options exercised	(8,249,893	)	5.26
Options forfeited/canceled	(1,360,202	)	10.04
Balance as of October 31, 2018	36,749,854		$	8.22	5.6	$	439,185
Vested and exercisable as of October 31, 2018	26,221,996		$	6.38	5.2	$	361,783

The aggregate intrinsic value of options vested and exercisable as of October 31, 2018 is calculated based on the difference between the exercise price and the closing price of $20.18 of our Class A common stock on October 31, 2018.

As of October 31, 2018, total unrecognized employee compensation cost related to outstanding options was $40.2 million, which is expected to be recognized over a weighted-average period of approximately 1.9 years.

Restricted Stock Units

A summary of the restricted stock unit activity under our 2015 Plan and related information is as follows:



	Number of Restricted Stock Units Outstanding		Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value (in thousands)
Unvested balance as of January 31, 2018	17,682,646		$	12.60	$	356,117
Granted	11,098,371		22.49
Vested	(6,429,146	)	12.84
Forfeited	(1,719,729	)	15.57
Converted	(1,142,838	)	11.86
Unvested balance as of October 31, 2018	19,489,304		$	17.92	$	393,270

As of October 31, 2018, total unrecognized employee compensation cost related to unvested restricted stock units was $316.1 million, which is expected to be recognized over a weighted-average period of approximately 3.0 years.

In March 2017, we granted 750,000 performance stock units (net of 77,000 canceled units), at a target percentage of 100%, with both performance and service vesting conditions payable in common shares, from 0% to 150% of the target number granted, contingent upon the degree to which the performance condition is met. In March 2018, a total of 780,000 shares was earned based on the performance condition achieved and these shares are subject to service conditions through the vesting periods. Stock-based compensation expense for these performance stock units, recognized on an accelerated attribution method, was $1.3 million and $0.4 million for the three months ended October 31, 2017 and 2018, and $2.9 million and $1.9 million for the nine months ended October 31, 2017 and 2018.

In August 2017, we granted 464,744 performance stock units, at a target percentage of 100%, with both performance and service vesting conditions payable in common shares, from 0% to 150% of the target number granted, contingent upon the degree to which the performance condition is met. The grant date for these awards was subsequently established when the performance condition was determined in March 2018, and these awards were contemporaneously converted to restricted stock. See below for further discussion.

Restricted Stock

In March 2018, we converted certain restricted stock units and performance stock units that were previously granted into 1,375,210 shares of restricted stock for corporate tax benefit purposes. Of the 1,375,210 shares of restricted stock, 697,116 shares are performance restricted stock and 678,094 shares are subject to service vesting conditions only. The conversion did not change the fair value or vesting conditions and therefore no modification accounting was required.

During the nine months ended October 31, 2018, we issued 1,954,908 shares of performance restricted stock at the maximum performance percentage of 180%, with vesting contingent upon the degree to which the performance condition is met. The shares may be earned from 0% to 180%. Actual shares earned may be lower than the aggregate maximum number dependent on the degree to which the performance condition is met, and cannot be higher than the aggregate maximum number. Any portion of shares that are not earned will be canceled.

A summary of the restricted stock activity under our 2015 Plan and related information is as follows:



	Number of Restricted Stock Units Outstanding		Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value (in thousands)
Unvested balance as of January 31, 2018	—		$	—	$	—
Granted and converted	3,330,118		19.25
Vested	(116,186	)	12.84
Unvested balance as of October 31, 2018	3,213,932		$	19.49	$	64,857

All unvested restricted shares are subject to cancellation to the extent vesting conditions are not met. Stock-based compensation expense for performance restricted stock is recognized on an accelerated attribution method. In the three and nine months ended October 31, 2018, we recognized $7.5 million and $17.7 million in stock-based compensation expense relating to restricted stock. As of October 31, 2018, total unrecognized employee compensation cost related to unvested restricted stock was $26.3 million, which is expected to be recognized over a weighted-average period of approximately 2.4 years.

Stock-Based Compensation Expense

The following table summarizes the components of stock-based compensation expense recognized in the condensed consolidated statements of operations (in thousands):



	Three Months Ended October 31,				Nine Months Ended October 31,
	2017		2018		2017		2018
Cost of revenue—product	$	143	$	862	$	898	$	2,190
Cost of revenue—support subscription	2,422		3,327		6,441		8,940
Research and development	18,073		24,634		51,632		67,956
Sales and marketing	12,104		18,681		34,169		49,890
General and administrative	6,121		10,825		14,780		26,962
Total stock-based compensation expense	$	38,863	$	58,329	$	107,920	$	155,938

The tax benefit related to stock-based compensation expense for all periods presented was not material.