Earlier this year Microsoft revealed that its once Windows 10 and Xbox One exclusive fighting game, Killer Instinct, will come to Steam later this year. Now we have another interesting piece of information: The Steam version of Killer Instinct will support cross-play with both Windows Store and Xbox One console versions of the game.
Killer Instinct community manager, Rukari Austin, announced this in a post on official KI forums. He informed us that the cross-play feature will be implemented into current Killer Instinct versions (i.e. Windows Store and Xbox) with the 3.9 Content Update. Apparently there'll be a switch/button to enable cross-play; because he wrote, "tucked away in this CU is a switch that will enable certain feature you’ve all been clamoring for, and that feature is indeed cross-play!"
Keep in mind this feature is fresh and still being tested. So there will be some occasions when the cross-play feature will not be available. Austin said, if that happens "never fear, that is simply us working on things in the background".
But it'll not interrupt cross-play between Windows Store and Xbox One. Only Steam players will be isolated from them temporarily. "So please, play to your heart’s content while [they] do the dirty work in the background."