We maintain two equity incentive plans: the 2009 Equity Incentive Plan (the 2009 Plan) and the 2015 Equity Incentive Plan (the 2015 Plan). The 2015 Plan became effective in connection with our initial public offering (IPO) in October 2015 and serves as the successor to our 2009 Plan. The 2015 Plan provides for grants of incentive stock options to our employees and non-statutory stock options, stock appreciation rights, restricted stock, restricted stock unit awards (RSUs), performance stock awards, performance cash awards, and other forms of stock awards to our employees, directors and consultants. No new awards have been issued under our 2009 Plan after the effective date of our 2015 Plan. Outstanding awards granted under our 2009 Plan will remain subject to the terms of our 2009 Plan and applicable award agreements, until such outstanding awards that are stock options are exercised, terminated or expired by their terms.

Starting in December 2018, we net-share settle equity awards held by certain employees by withholding shares upon vesting to satisfy tax withholding obligations. The shares withheld to satisfy employee tax withholding obligations are returned to our 2015 Plan and will be available for future issuance. Payments for employees’ tax obligations to the tax authorities are recognized as a reduction to additional paid-in capital and reflected as a financing activity in our consolidated statements of cash flows.

We initially reserved 27,000,000 shares of our common stock for issuance under our 2015 Plan. The number of shares reserved for issuance under our 2015 Plan increases automatically on the first day of each fiscal year through 2025, in an amount equal to 5% of the total number of shares of our capital stock outstanding as of the immediately preceding January 31.

Our 2015 Employee Stock Purchase Plan became effective in connection with our IPO and was amended and restated in fiscal 2019 (2015 ESPP). A total of 3,500,000 shares of common stock was initially reserved for issuance under the 2015 ESPP and an additional 5,000,000 shares of common stock were added in connection with the amendment and restatement. The number of shares reserved for issuance under our 2015 ESPP increases automatically on the first day of February of each of 2016 through 2025, in an amount equal to the lesser of (i) 1% of the total number of shares of our capital stock outstanding as of the immediately preceding January 31, and (ii) 3,500,000 shares of common stock.

Our board of directors (or a committee thereof) has the authority under the 2015 ESPP to establish the length and terms of the offering periods and purchase periods and the purchase price of the shares of common stock which may be purchased under the plan. The current offering terms allow eligible employees to purchase shares of our 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). In February 2019, we amended the offering terms under the 2015 ESPP, on a prospective basis, to include an additional dollar cap of $7,500 per purchase period. The current terms also allow for a 24-month offering period beginning March 16th and September 16th of each year, with each offering period consisting of four 6 months purchase periods, subject to a reset provision. Further, currently, on each purchase date, eligible employees may purchase our common stock at a price per share equal to 85% of the lesser of the fair market value of our common stock (1) on the first trading day of the applicable offering period or (2) the purchase date.

Under the reset provision currently authorized, 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 charge to be recognized over the new offering period. During fiscal 2018 and 2020, multiple ESPP resets resulted in total modification charges of $9.0 million and $13.6 million, respectively, to be recognized over the new offering periods. There was no ESPP reset during fiscal 2019.

During fiscal 2018, 2019 and 2020, we recognized $18.3 million, $35.4 million and $24.5 million, of stock-based compensation expense related to our 2015 ESPP. At the end of fiscal 2020, there was $27.6 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 1.6 years.


	Options Outstanding
	Number of Shares	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (Years)	Aggregate Intrinsic Value (in thousands)
Balance at the end of fiscal 2019	35,465,543	$	8.34	5.4	$	339,591

Options exercised	(7,770,157)	5.53
Options forfeited/canceled	(873,143)	13.91
Balance at the end of fiscal 2020	26,822,243	$	8.97	3.9	$	237,803
Vested and exercisable at the end of fiscal 2020	23,665,389	$	8.12	4.4	$	229,523

The aggregate intrinsic value of options vested and exercisable at the end of fiscal 2020 is calculated based on the difference between the exercise price and the closing price of $17.80 of our common stock on the last day of fiscal 2020. The aggregate intrinsic value of options exercised during fiscal 2018, 2019 and 2020 was $104.9 million, $165.0 million and $106.6 million.

During fiscal 2018, 2019 and 2020, we recognized $49.0 million, $32.0 million and $15.8 million, of stock-based compensation expense related to stock options. The weighted-average grant date fair value of options granted was $5.57 per share for fiscal year 2018 and no options were granted in fiscal 2019 and 2020. The total

The fair value of stock options granted to employees and to be purchased under ESPP is estimated on the grant date using the Black-Scholes option pricing model. This valuation model for stock-based compensation expense requires us to make assumptions and judgments about the variables used in the calculation including the fair value of the underlying common stock, expected term, the expected volatility of the common stock, a risk-free interest rate and expected dividend yield.


	Fiscal Year Ended
	2018		2019	2020
Employee Stock Options
Expected term (in years)	6.1		n/a	n/a
Expected volatility	47	%	n/a	n/a
Risk-free interest rate	1.9	%	n/a	n/a
Dividend rate	—		n/a	n/a
Fair value of common stock	$12.84		n/a	n/a
Employee Stock Purchase Plan
Expected term (in years)	0.5 - 2.0		0.5 - 2.0	0.5 - 2.0
Expected volatility	35% - 39%		44% - 47%	42% - 47%
Risk-free interest rate	0.9% - 1.4%		2% - 2.8%	1.7% - 2.5%
Dividend rate	—		—	—
Fair value of common stock	$10.39 - $14.65		$20.62 - $27.66	$17.76 - $20.87

Expected Term—The expected term represents the period that our stock-based awards are expected to be outstanding. The expected term assumptions were determined based on the vesting terms, exercise terms and contractual lives of the options and ESPP purchase rights.

Expected Volatility—Starting in fiscal 2019, the expected volatility for ESPP purchase rights is based on the historical volatility of our common stock for a period equivalent to the expected term of the ESPP purchase rights. Prior to fiscal 2019, since we had limited trading history of our common stock, the expected volatility was derived from the average historical stock volatilities of several public companies within the same industry that we considered to be comparable to our business over a period equivalent to the expected term of the stock option grants and ESPP purchase rights.

Risk-Free Interest Rate—The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term of the stock option grants and ESPP purchase rights.


	Number of RSUs Outstanding	Weighted-Average Grant Date Fair Value		Aggregate Intrinsic Value (in thousands)
Unvested balance at the end of fiscal 2019	21,917,550	$	17.94	$	392,515
Granted	15,780,796	18.91
Vested	(9,241,583)	17.12
Forfeited	(3,022,166)	18.93

Unvested balance at the end of fiscal 2020	25,434,597	$	18.72	$	452,736

During fiscal 2018, 2019 and 2020, we recognized $83.4 million, $119.9 million and $161.8 million in stock-based compensation expense related to RSUs. At the end of fiscal 2020, total unrecognized employee compensation cost related to unvested RSUs was $435.2 million, which is expected to be recognized over a weighted-average period of approximately 3.0 years.

•1,291,194 shares were issued at the target percentage of 100%, with both performance and service vesting conditions payable in common shares, from 0% to 160% of the target number granted, contingent upon the degree to which the performance condition is met. A total of 930,678 shares were earned at the end of fiscal 2020 based on the performance condition achieved and these shares are subject to service conditions through the vesting periods. The remaining shares will be canceled in fiscal 2021.


	Number of Restricted Stock Outstanding	Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value (in thousands)
Unvested balance at the end of fiscal 2019	2,267,569	$	18.70	$	40,612
Granted	1,399,688	20.30
Vested	(1,284,638)	18.97
Forfeited/canceled	(255,413)	19.93
Unvested balance at the end of fiscal 2020	2,127,206	$	19.58	$	37,864

During fiscal 2019 and 2020, we recognized $23.3 million and $24.6 million in stock-based compensation expense related to restricted stock. At the end of fiscal 2020, total unrecognized employee compensation cost related to unvested restricted stock was $14.2 million, which is expected to be recognized over a weighted-average period of approximately 1.8 years.


	Fiscal Year Ended
	2018		2019		2020
Cost of revenue—product	$	1,630	$	2,951	$	3,732
Cost of revenue—subscription services	9,050		12,378		14,403
Research and development	71,229		92,484		107,658
Sales and marketing	47,687		66,350		67,560
General and administrative	21,077		36,482		33,352
Total stock-based compensation expense	$	150,673	$	210,645	$	226,705