Halo 4 will interact with Microsoft's upcoming tablet computer, Surface. Exactly how the two will interact, however, remains a mystery. Mattrick noted the news during a VentureBeat event in San Francisco yesterday; later, he reconfirmed the functionality with a reporter on-hand but refused to give any more details.
If we had to guess, though, we'd say the only functionality between the two will be the already announced SmartGlass features from E3 (say, using Halo Waypoint, or viewing the game's encyclopedia). After all, Microsoft told us at E3 that SmartGlass will be part of all Microsoft Studios games going forward after its fall 2012 launch.
Of course, Microsoft could always go totally off the rails and add full-on gamepad support via Surface's touchscreen. Or maybe just a personal Cortana app where she freaks out and yells at you randomly while you're playing. Maybe they should just stick with the Waypoint stuff.