[CONFIRMED] Smartglass will function as a game controller and second screen.

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Xbox One features Wi-Fi Direct, the ability for the Xbox One to act as an access point for Wi-Fi enabled devices, and partner with other Wi-Fi Direct devices.

Smartglass-enabled tablets and smartphones will be able to act as a controller for Xbox One with latent performace as good as an Xbox One wireless controller.  In terms of a Smartglass device as a second screen, this will largely depend on the device and the GPU performance for video compression/decompression.  However, higher end devices should be able to provide 20ms latency for remote gaming up to 600 ft away (Line of Sight) or 300 ft otherwise.

Also, if game developers add support for it, the Xbox One will support keyboard and mouse via Wi-Fi Direct.