Valve has released the previously announced Steam Link app as an open beta.
I was stunned at how well the stream held up when playing games like Far Cry 5, Doom, and Rocket League on my iPad. In addition to that, if you want to stream to your mobile device, it needs to be connected to a 5GHz Wi-Fi network. With it, you can play your collection of Steam titles on your smartphone, provided you've a powerful computer to run said games and you're under the same roof.
On the Apple side, we support any iOS device running iOS 10 or newer, and any Apple TV running tvOS 10.3 or newer. It's possible that black bars on the edges will appear on your mobile device since this is how the app is dealing with the aspect ratio differences, but you can use two-finger pinch and pan gestures to zoom in.