Under our 2012 Stock Plan, RSUs or stock options may be granted. An RSU award is an agreement to issue shares of our publicly traded stock at the time the award vests. Incentive and non-qualified stock options, or rights to purchase common stock, are generally granted for a term of 10 years. RSUs granted to participants under the 2012 Stock Plan generally vest over four years contingent upon employment or service with us on the vesting date.

As of December 31, 2019, there were 37,982,435 shares of stock reserved for future issuance under our Stock Plan.

Additionally, we have stock-based awards that may be settled in the stock of certain of our Other Bets.

For the years ended December 31, 2017, 2018 and 2019, total stock-based compensation expense was $7.9 billion, $10.0 billion and $11.7 billion, including amounts associated with awards we expect to settle in Alphabet stock of $7.7 billion, $9.4 billion, and $10.8 billion, respectively.

For the years ended December 31, 2017, 2018 and 2019, 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 $1.6 billion, $1.5 billion, and $1.8 billion, respectively.

For the years ended December 31, 2017, 2018 and 2019, tax benefit realized related to awards vested or exercised during the period was $2.7 billion, $2.1 billion and $2.2 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 RSUs in Alphabet stock for the year ended December 31, 2019:



	Unvested Restricted Stock Units
	Number of Shares		Weighted- Average Grant-Date Fair Value
Unvested as of December 31, 2018	18,467,678		$	936.96
Granted	13,934,041		$	1,092.36
Vested	(11,576,766	)	$	919.28
Forfeited/canceled	(1,430,717	)	$	990.56
Unvested as of December 31, 2019	19,394,236		$	1,055.22

The weighted-average grant-date fair value of RSUs granted during the years ended December 31, 2017 and 2018, was $845.06 and $1,095.89, respectively. Total fair value of RSUs, as of their respective vesting dates, during the years ended December 31, 2017, 2018, and 2019 were $11.3 billion, $14.1 billion, and $15.2 billion, respectively.

As of December 31, 2019, there was $19.1 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 $448 million, $691 million, and $724 million for the years ended December 31, 2017, 2018, and 2019, respectively.