Known as Steam Link Anywhere, the new feature is now in beta and will let users play his or her Steam library from any computer supporting Steam.
This service is an extension of Steam Link, which allows users to stream games from their desktop PC to a compatible device over an Internet connection.
With so many companies exploring game streaming services Valve has something of an edge in that PC gamers are likely to already have a library of games to play from their smartphones.
Update: Dec. 20, 2018 - Valve is no longer selling the Steam Link hardware, but it will continue to update and support the Steam Link app going forward. After that, follow the simple instructions laid out here to get started.
Unfortunately, there is still no word on Steam Link availability on iOS, so those who were waiting to enjoy this on an iPad or iPhone are out of luck for now. Your Steam Client also needs to be on the latest beta build, which will be dated March 13 or newer. It normally works by connecting a mobile device to a host computer via a local network.
This streaming of games is one of the use cases for 5G. Next, add a computer and then click on "Other Computer". Obviously, you'll need a good connection on both devices to make it worthwhile.