In August 2011, we established the Groupon, Inc. 2011 Stock Plan (the "2011 Plan"), most recently amended in March 2023, under which options, restricted stock units and performance stock units for up to 13,775,000 shares of Common Stock were authorized for future issuance to employees, consultants and directors. The 2011 Plan is administered by the Compensation Committee of the Board (the "Compensation Committee"). As of December 31, 2023, 2,869,211 shares of Common Stock were available for future issuance under the 2011 Plan.

The stock-based compensation expense related to stock awards issued under the 2011 Plan and acquisition-related awards are presented within the following line items of the Consolidated Statements of Operations for the years ended December 31, 2023, 2022 and 2021 (in thousands):


	Year Ended December 31,
	2023		2022		2021
Cost of revenue	$	119	$	395	$	585
Marketing	53		1,054		748
Selling, general and administrative	14,309		28,557		31,836
Total stock-based compensation expense	$	14,481	$	30,006	$	33,169

We capitalized $0.6 million, $3.4 million and $3.7 million of stock-based compensation for the years ended December 31, 2023, 2022 and 2021, in connection with internally-developed software and cloud computing arrangements.

The Groupon, Inc. 2012 Employee Stock Purchase Plan ("ESPP"), as amended, authorizes us to grant up to 1,000,000 shares of Common Stock under that plan. For the years ended December 31, 2023, 2022 and 2021, 45,879, 83,551 and 49,399 shares of Common Stock were issued under the ESPP.

The restricted stock units granted under the 2011 Plan ("Restricted Stock Units") generally have vesting periods between one and four years and are amortized on a straight-line basis over their requisite service period.


	Restricted Stock Units	Weighted- Average Grant Date Fair Value (per share)
Unvested at December 31, 2022	2,876,089	$	19.33
Granted	601,314	5.26
Vested	(1,368,015)	19.04
Forfeited	(1,363,548)	15.72
Unvested at December 31, 2023	745,840	$	10.61

The weighted-average grant date fair value of Restricted Stock Units granted in 2022 and 2021 was $16.95 and $31.48. The fair value of Restricted Stock Units that vested during each of the three years ended December 31, 2023, 2022 and 2021 was $8.9 million, $15.6 million and $48.8 million. As of December 31, 2023, $4.4 million of unrecognized compensation costs related to unvested employee Restricted Stock Units are expected to be recognized over a remaining weighted-average period of 0.64 years.

On March 30, 2023, we issued 3,500,000 units of stock options with a per share value of $0.95, a strike price of $6.00 and vesting over two years. The exercise price of stock options granted is equal to the fair market value of the underlying stock on the date of grant. The contractual term for these stock options expires three years from the grant date. The fair value of stock options on the grant date is amortized on a straight-line basis over the requisite service period.

The fair value of stock options granted is estimated on the date of grant using the Black-Scholes-Merton option-pricing model. Expected volatility is based on Groupon's historical volatility over the estimated expected life of the stock options. The expected term represents the period of time the stock options are expected to be outstanding. The risk-free interest rate is based on yields on U.S. Treasury STRIPS with maturity similar to the estimated expected life of the stock options. The weighted-average assumptions for stock options granted are outlined in the following table:


	Options	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022	—	$	—	—	$	—
Granted	3,500,000	6.00		3.00	—
Exercised	(437,500)	6.00		—	—
Outstanding at December 31, 2023	2,187,500	6.00		2.25	14,963
Exercisable at December 31, 2023	875,000	$	6.00	2.25	5,985

As of December 31, 2023, there was $2.1 million of total unrecognized compensation costs related to unvested stock options granted under the 2011 Plan. That cost is expected to be recognized over a weighted-average period of 1.25 years. The total fair value of shares vested during the year ended December 31, 2023 was $0.8 million.

We have granted performance share units under the 2011 Plan that vest in shares of our Common Stock upon the achievement of financial and operational targets specified in the respective award agreement ("Performance Share Units"). Our existing Performance Share Units are subject to continued service through the performance period dictated by the award and certification by the Compensation Committee of the Board that the specified performance conditions have been achieved.


	Performance Share Units	Weighted-Average Grant Date Fair Value (per unit)
Unvested at December 31, 2022	17,269	$	24.13
Granted	506,324	6.34
Vested	(17,269)	24.13
Unvested at December 31, 2023	506,324	$	6.34

Maximum shares issuable upon vesting at December 31, 2023	759,486

As of December 31, 2023, unrecognized compensation costs related to unvested Performance Share Units were $1.2 million. That cost is expected to be recognized over a remaining weighted-average period of 0.33 years.

We have also previously granted performance share units subject to a market condition ("Market-based Performance Share Units"). As of December 31, 2023, there were no Market-based Performance Share Units outstanding. During the year ended December 31, 2022, 24,335 Market-based Performance Share Units were forfeited and 33,333 Market-based Performance Share Units expired as the market conditions were not met. No Market-based Performance Share Units remain unvested and all related compensation costs have been recognized as of December 31, 2022.

We have a 401(k) defined contribution retirement savings plan covering substantially all domestic employees. Each participant may elect to defer a portion of his or her compensation subject to certain limitations. We contribute up to 50% of the first 6% of eligible compensation contributed to the plan, subject to a 3 year graded vesting schedule. We also have several foreign defined contribution plans, which require us to contribute a percentage of participating employee's salary according to local regulations. During the years ended December 31, 2023, 2022 and 2021, our contributions for all plans were $1.9 million, $5.8 million and $6.7 million.