Halo 4 developer 343 Industries announced its next Halo game moments ago at Microsoft's pre-E3 press conference. It's known as Halo Xbox One, not Halo 5, whatever that means.
This latest sequel is due sometime in 2014.
It's not clear if this is a numbered sequel or a spin-off, but it features Master Chief and runs at 60 frames-per-second.
The announcement trailer, below, shows Master Chief wandering through the desert sporting jedi robes over his trademark armor. He then resurrects a giant mech that rises out of the ground.