It's called Steam Remote Play.
Steam In-Home Streaming service which lets you stream Steam games between different devices that share a network, has "experimentally" been unshackled and is now available outside the home, too. Given the change, it's got a new name, Steam Remote Play, and you can try it out now.
As long as both devices you're running Steam have a good connection and are close to a Steam datacentre, you should be able to stream games between each other wherever they are. You will probably still want a wired connection, though. Even with a 5GHz router, I've found playing faster and flashier games over Wi-fi that comes with too many concessions.
Here are the rest of the changes to Remote Play:
- In-Home Streaming, settings have been renamed as Remote Play settings
- Paired Steam Link devices now show up in the Remote Play settings
- You can now remove all paired Steam Linked devices
- Fixed the PC to PC streaming client hanging when you alt-tab away from it
- Added a network status icon to indicate that the network connection is slow.
In the meantime, here are the full patch notes for the latest Steam client update.