The Xbox One version of the game is due out on November18. Rockstar says:
Available in both GTAV and GTA Online, we've made a host of changes to accommodate this new perspective, including the creation of an optional first-person cover system, a new targeting system, a more traditional FPS control scheme, and integrating thousands of new animations into the existing game. It's also available at the touch of a button so you can quickly switch back and forth between perspectives.
The new mode will also be included in the PlayStation 4 version that comes out on the same say and the PC version that's due for release in January. Will the new mode offer a better or worse way to play GTA V?
Source: Rockstar Games