We have issued performance-based stock options and performance-based RSUs, the vesting of which is generally contingent upon the achievement of certain performance criteria related to our operating performance, as well as successful and timely development and market acceptance of future product introductions. In addition, certain of the performance RSUs have additional service requirements subsequent to the achievement of the performance criteria. Compensation expense is recognized over the requisite service period, which is defined as the longest explicit, implicit or derived service period based on management’s estimate of the probability of the performance criteria being satisfied, adjusted at each balance sheet date. For both service-based and performance-based RSUs, we account for forfeitures as they occur as a reduction to stock-based compensation expense and additional paid-in-capital.

For performance-based options with a vesting schedule based entirely on the attainment of both performance and market conditions, stock-based compensation expense is recognized for each pair of performance and market conditions over the longer of the expected achievement period of the performance and market conditions, beginning at the point in time that the relevant performance condition is considered probable of achievement. The fair value of such awards is estimated on the grant date using Monte Carlo simulations.

On May 24, 2018, our stockholders approved the Board of Directors’ grant of 6,365,856 stock option awards to Patrick W. Smith, our CEO (the “CEO Performance Award”). The CEO Performance Award consists of 12 vesting tranches with a vesting schedule based entirely on the attainment of both operational goals (performance conditions) and market capitalization goals (market conditions), assuming continued employment either as the CEO or as both Executive Chairman and Chief Product Officer and service through each attainment date. Each of the 12 vesting tranches of the CEO Performance Award have a 10-year contractual term and will vest upon certification by the Compensation Committee of the Board of Directors that both (i) the market capitalization goal for such tranche, which begins at $2.5 billion for the first tranche and increases by increments of $1.0 billion thereafter, and (ii) any one of the following eight operational goals focused on revenue or eight operational goals focused on Adjusted EBITDA have been met for the previous four consecutive fiscal quarters. Adjusted EBITDA for purposes of the CEO Performance Award ("Adjusted EBITDA (CEO Performance Award)") is defined as net income (loss) attributable to common stockholders before interest expense, interest

and other income (such as dividends) earned on investments in marketable securities, provision (benefit) for income taxes, depreciation and amortization, and stock-based compensation expense.

(1)	In connection with the business acquisition that was completed during the three months ended June 30, 2018, the revenue goals were adjusted for the acquiree’s Target Revenue, as defined in the CEO Performance Award agreement.

As of June 30, 2021, the following operational goals were achieved, with vesting of the related tranches pending certification by the Compensation Committee:

●

Adjusted EBITDA (CEO Performance Award) of $175.0 million, $190.0 million, $200.0 million, $210.0 million, and $220.0 million.

As of June 30, 2021, the following operational goals were considered probable of achievement:

●

Adjusted EBITDA (CEO Performance Award) of $230.0 million.

●

Total revenue of $860.1 million, $1,010.1 million, and $1,210.1 million; and

As of June 30, 2021, the following operational goals were previously achieved and the related tranches vested:

●

Adjusted EBITDA (CEO Performance Award) of $125.0 million and $155.0 million

●

Total revenue of $710.1 million

Stock-based compensation expense associated with the CEO Performance Award is recognized over the requisite service period, which is defined as the longest explicit, implicit or derived service period, based on management’s estimate of the probability and timing of the performance criteria being satisfied, adjusted at each balance sheet date. Expense recognition begins at the point in time when the relevant operational goal is considered probable of being met. The probability of attaining an operational goal and the expected attainment date for meeting a probable operational goal are based on a subjective assessment of our forward-looking financial projections, taking into consideration statistical analysis when considered appropriate. The statistical model and the assessment that determine the estimated attainment dates are subject to a number of estimated inputs, including expected volatility rates, management’s forward-looking financial projections, in particular for operational goals that are anticipated to be attained in the near future, and adjustment of other estimates based on the passage of time.

Beginning with the three months ended June 30, 2021, management discontinued consideration of the statistical model based on actual and anticipated attainment of the remaining operational goals. During the three months and six months ended June 30, 2021, we recorded an additional $107.3 million and $158.7 million, respectively, in stock-based

compensation expense as a result of updated estimates for the CEO Performance Award and eXponential Stock Performance Plan (discussed below).

The first eight market capitalization goals have been achieved as of June 30, 2021. As of June 30, 2021, 1.6 million stock options have vested. As twelve operational goals are considered probable of achievement, we recorded stock-based compensation expense of $204.2 million related to the CEO Performance Award from the Grant Date through June 30, 2021. The number of stock options that would vest related to the remaining unvested tranches is approximately 4.8 million shares. As of June 30, 2021, we had $41.7 million of total unrecognized stock-based compensation expense for the performance goals that were considered probable of achievement, which will be recognized over a weighted-average period of 1.57 years.

eXponential Stock Performance Plan

On February 12, 2019, our shareholders approved the 2019 Stock Incentive Plan (the “2019 Plan”), which was adopted by the Board of Directors to reserve a sufficient number of shares to facilitate our eXponential Stock Performance Plan (“XSPP”) and grants of eXponential Stock Units (“XSUs”) under the plan. Initial awards under the plan were granted in January 2019, with additional employee awards granted since that date. During the three and six months ended June 30, 2021 we granted an additional twenty three thousand and thirty three thousand XSUs, respectively.

The XSUs are grants of RSUs, each with a term of approximately nine years, that vest in 12 equal tranches. Each of the 12 tranches will vest upon certification by the Compensation Committee of the Board of Directors that both (i) the market capitalization goal for such tranche, which begins at $2.5 billion for the first tranche and increases by increments of $1.0 billion thereafter, and (ii) any one of eight operational goals focused on revenue or eight operational goals focused on Adjusted EBITDA (CEO Performance Award) have been met for the previous four consecutive fiscal quarters. Beginning with the quarter ended June 30, 2021, new XSU grants are divided into a reduced number of tranches depending on employee eligibility and current market capitalization attainment.

The XSPP contains an anti-dilution provision incorporated into the plan based on shareholder feedback, which affects the calculation of the market capitalization goals in the plan. The plan defines a maximum number of shares outstanding that may be used in the calculation of the market capitalization goals (the “XSU Maximum”). If the actual number of shares outstanding exceeds the XSU Maximum guardrail, then the lower pre-defined number of shares in the XSU Maximum, rather than the higher actual number of shares outstanding, is used to calculate market capitalization for the determination of the market capitalization goals in the XSPP, which, together with the operational goals, determines whether XSUs vest for participating employees.

The XSU Maximum is defined as the actual number of shares outstanding on the original XSU grant date of January 2, 2019, increased by a 3% annual rate over the term of the XSPP and by shares issued upon the exercise of CEO Performance Award options. The XSU Maximum is also adjusted for acquisitions, spin-offs or other changes in the number of outstanding shares of common stock, if such changes have a corresponding adjustment on the market capitalization goals.

New shares issued for any other reasons, including shares issued upon vesting of XSUs, RSUs, and Performance Stock Units (“PSUs”) as well as shares issued to raise capital through equity issuances or in other transactions, do not increase the XSU Maximum.

The market capitalization and operational goals are identical to the CEO Performance Award, but a different number of shares is used to calculate the market capitalization goals if shares outstanding exceed the XSU Maximum. Additionally, because the grant date is different than that of the CEO Performance Award, the measurement period for market capitalization is not identical. As of June 30, 2021, actual shares outstanding exceeded the XSU Maximum as a result of the common stock offering completed in June 2020. Accordingly, market capitalization as calculated for the purposes of achieving additional goals uses the lower XSU Maximum share amount rather than actual shares outstanding.

The first eight market capitalization goals have been achieved as of June 30, 2021. The first XSU tranche vested in March 2021, and the second and third tranches vested in May 2021. As all twelve operational goals are considered probable of achievement, we recorded stock-based compensation expense of $151.4 million related to the XSU awards from their respective grant dates through June 30, 2021. The number of XSU awards that would vest related to the remaining nine tranches is approximately 4.0 million shares. As of June 30, 2021, we had $42.3 million of total unrecognized stock-based compensation expense, which will be recognized over a weighted-average period of 2.20 years.

Restricted Stock Units

The following table summarizes RSU activity for the six months ended June 30, 2021 (number of units and aggregate intrinsic value in thousands):


	Number of	Weighted Average		Aggregate
	Units	Grant-Date Fair Value		Intrinsic Value
Units outstanding, beginning of year	1,107	$	76.10
Granted	98		149.92
Released	(276)		51.65
Forfeited	(64)		98.43
Units outstanding, end of period	865		90.59	$	152,892

Aggregate intrinsic value represents our closing stock price on the last trading day of the period, which was $176.80 per share, multiplied by the number of RSUs outstanding. As of June 30, 2021, there was $57.4 million in unrecognized compensation costs related to RSUs under our stock plans for shares that are expected to vest. We expect to recognize the cost related to the RSUs over a weighted average period of 2.10 years. RSUs are released when vesting requirements are met.

Certain RSUs that vested in the six months ended June 30, 2021 were net-share settled such that we withheld shares to cover the employees’ tax obligation for the applicable income and other employment taxes, and remitted the cash to the appropriate taxing authorities. Total shares withheld related to RSUs were forty six thousand and had a value of $7.5 million on their respective vesting dates as determined by the closing stock price on such dates. Payments for the employees’ tax obligations are reflected as a financing activity within the condensed consolidated statements of cash flows. We record a liability for the tax withholding to be paid by us as a reduction to additional paid-in capital.

Performance Stock Units

The following table summarizes PSU activity, inclusive of XSUs, for the six months ended June 30, 2021 (number of units and aggregate intrinsic value in thousands):


	Number of	Weighted Average		Aggregate
	Units	Grant-Date Fair Value		Intrinsic Value
Units outstanding, beginning of year	5,618	$	35.71
Granted	225		50.00
Released	(1,696)		41.20
Forfeited	(60)		35.80
Units outstanding, end of period	4,087		34.22	$	722,593

Aggregate intrinsic value represents our closing stock price on the last trading day of the period, which was $176.80 per share, multiplied by the number of PSUs outstanding. As of June 30, 2021, there was $44.8 million in unrecognized compensation costs related to PSUs under our stock plans for shares that are expected to vest. We expect to recognize the cost related to the PSUs over a weighted average period of 2.22 years. PSUs are released when vesting requirements are met.

As of June 30, 2021, the performance criteria had been met for approximately 2.2 million of the 4.1 million PSUs outstanding.

On March 8 and May 17, 2021, the Compensation Committee of our Board of Directors approved waivers of the holding period requirements for each XSPP participant who is an Arizona resident and elected to receive XSUs in lieu of On-Target Earnings. This waiver releases the holding period requirements to allow participants the ability to choose to sell a portion of their vested shares to satisfy new income tax obligations pursuant to Arizona Proposition 208, which was passed in the November 2020 state-wide election. This waiver applied only to 4% of the XSUs for the impacted participants which vested on March 8 and May 17, 2021, amounting to approximately 36 thousand shares. The remainder of the shares not sold to satisfy tax obligations are subject to a 2.5 year minimum holding period. We accounted for this change as a Type I modification under ASC 718 since there was no impact on attainment of the operational or market capitalization goals. We recognized additional stock-based compensation expense of $0.5 million and $0.9 million for the three months and six months ended June 30, 2021, respectively, because of this modification.

Certain PSUs that vested in the six months ended June 30, 2021 were net-share settled such that we withheld shares to cover the employees’ tax obligation for the applicable income and other employment taxes, and remitted the cash to the appropriate taxing authorities. Total shares withheld related to PSUs were approximately nineteen thousand and had a value of $2.8 million on their respective vesting dates as determined by the closing stock price on such dates. Payments for the employees’ tax obligations are reflected as a financing activity within the condensed consolidated statements of cash flows. We record a liability for the tax withholding to be paid by us as a reduction to additional paid-in capital.

Stock Option Activity

The following table summarizes stock option activity for the six months ended June 30, 2021 (number of units and aggregate intrinsic value in thousands):


				Weighted
		Weighted		Average
	Number	Average		Remaining
	of	Exercise		Contractual	Aggregate
	Options	Price		Life (years)	Intrinsic Value
Options outstanding, beginning of year	6,366	$	28.58
Granted	—		—
Exercised	—		—
Expired / terminated	—		—
Options outstanding, end of period	6,366		28.58	6.66	$	943,547
Options exercisable, end of period	4,243		28.58	6.66		629,031

Aggregate intrinsic value represents the difference between the exercise price of the underlying stock option awards and the closing market price of our common stock of $176.80 on June 30, 2021. There were no options exercised for the six months ended June 30, 2021. The intrinsic value of options exercised for the six months ended June 30, 2020 was $5.1 million. As of June 30, 2021, total options outstanding included 2.1 million unvested performance-based stock options, which relate to the CEO Performance Award and are probable of achievement.

Stock-based Compensation Expense

The following table summarizes the composition of stock-based compensation expense for the three and six months ended June 30, 2021 and 2020 (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Cost of products sold and services delivered	$	1,838	$	836	$	3,327	$	1,426
Sales, general and administrative expenses		114,089		26,766		185,104		41,736
Research and development expenses		21,622		6,233		38,728		10,868
Total stock-based compensation expense	$	137,549	$	33,835	$	227,159	$	54,030

Stock Incentive Plan

In February 2019, our shareholders approved the 2019 Plan authorizing an additional 6.0 million shares, plus remaining available shares under prior plans, for issuance under the new plan. Combined with the legacy stock incentive plans, there are 1.8 million shares available for grant as of June 30, 2021.

Stock Repurchase Plan

In February 2016, our Board of Directors authorized a stock repurchase program to acquire up to $50.0 million of our outstanding common stock subject to stock market conditions and corporate considerations. During the six months ended June 30, 2021 and 2020, no common shares were purchased under the program. As of June 30, 2021, $16.3 million remains available under the plan for future purchases. Any future purchases will be discretionary.