In May last year, Apple revoked initial approval of Valve's Steam link app from the App Store, barring users from streaming games to their iOS devices. A few days later, Cupertino cited a number of guideline violations behind the refusal but did give Apple users some hope for Steam Link's arrival in the future.
That time has come with the app now officially available on the App Store. "Just pair an MFI or Steam controller to your device, connect to a computer running Steam on the same local network, and start playing your existing Steam games." For those unaware, MFI refers to the Made for iPhone/iPod/iPad, a licensing program that Apple uses to certify gaming controllers such as the Steelseries Nimbus.
One major difference from the apps' Android version is that it doesn't allow game purchases from the Steam store. The removal of this functionality was to comply with Apple's new rules for remote mirroring apps dictating that any purchases through the app should be processed on the desktop PC, and not on the iPhone or iPad itself. What's strange is that Valve complied with this requirement in June last year so the app should have made its way to the App Store back then, but better late than never.
Steam Link is supported on devices running iOS 10 or higher with a "5Ghz network or wired Ethernet to a host computer running Steam."