It looks very probable now that Apple will announce a new version of the Apple TV that can run apps and games, at its event this evening.
iOS developer Steve Troughton Smith found references to "tvOS" in Apple's iTunes Connect: the official site for developers to submit apps and updates to Apple.
Specifically, the documentation mentions Game Center leaderboards appearing on Apple TV, giving credence to the rumours that the new Apple TV will have a focus on playing games.
The event is in one hour. You can find out where and how to watch it, here.