Our stock plans include the Alphabet 2012 Stock Plan and Other Bet stock-based plans. Under our stock plans, RSUs and other types of awards may be granted. An RSU award is an agreement to issue shares of our publicly traded stock at the time the award vests. RSUs granted to participants under the Alphabet 2012 Stock Plan generally vest over four years contingent upon employment or service with us on the vesting date.

As of December 31, 2020, there were 38,777,813 shares of stock reserved for future issuance under our Alphabet 2012 Stock Plan.

For the years ended December 31, 2018, 2019 and 2020, total stock-based compensation expense was $10.0 billion, $11.7 billion and $13.4 billion, including amounts associated with awards we expect to settle in Alphabet stock of $9.4 billion, $10.8 billion, and $12.8 billion, respectively.

For the years ended December 31, 2018, 2019 and 2020, we recognized tax benefits on total stock-based compensation expense, which are reflected in the provision for income taxes in the Consolidated Statements of Income, of $1.5 billion, $1.8 billion, and $2.7 billion, respectively.

For the years ended December 31, 2018, 2019 and 2020, tax benefit realized related to awards vested or exercised during the period was $2.1 billion, $2.2 billion and $3.6 billion, respectively. These amounts do not include the indirect effects of stock-based awards, which primarily relate to the research and development tax credit.

The following table summarizes the activities for our unvested Alphabet RSUs for the year ended December 31, 2020:


	Unvested Restricted Stock Units
	Number of Shares	Weighted- Average Grant-Date Fair Value
Unvested as of December 31, 2019	19,394,236	$	1,055.22
Granted	12,647,562	1,407.97
Vested	(11,643,670)	1,089.31
Forfeited/canceled	(1,109,335)	1,160.01
Unvested as of December 31, 2020	19,288,793	$	1,262.13

The weighted-average grant-date fair value of RSUs granted during the years ended December 31, 2018 and 2019, was $1,095.89 and $1,092.36, respectively. Total fair value of RSUs, as of their respective vesting dates, during the years ended December 31, 2018, 2019, and 2020 were $14.1 billion, $15.2 billion, and $17.8 billion, respectively.

As of December 31, 2020, there was $22.8 billion of unrecognized compensation cost related to unvested employee RSUs. This amount is expected to be recognized over a weighted-average period of 2.6 years.

We have two 401(k) Savings Plans that qualify as deferred salary arrangements under Section 401(k) of the Internal Revenue Code. Under these 401(k) Plans, matching contributions are based upon the amount of the employees’ contributions subject to certain limitations. We recognized expense of approximately $691 million, $724 million, and $855 million for the years ended December 31, 2018, 2019, and 2020, respectively.