Hmm...
Honestly, my money's on fake. First and foremost, that post doesn't contain a link to any video to support it's claims. Second, the description of Halo 4 has very simple and repetitive word choice. Not something you'd see in an official press release. It also seems to over promise on what the game will actually be, to the point of deviating from the core Halo experience. Player choice has never been a truly significant factor in the Halo series, especially not the numbered releases where you play as the Master Chief. The ability to customize weapons and vehicles is also something that is distinctly un-Halo, and far more reminiscent of an RPG. Also, this "Dark New Threat" is described a lot like the Flood. And "Cortana's" line about them coming back in greater numbers sounds like them saying it's the Flood without actually saying it's the Flood.
All in all, between the RPG like AIM system, vague information, repetative word choice, and allusions to the Flood, this white tiger is gonna call BS on this being legit info on Halo 4.
Oh, and about this: "On a technical level Halo 4 pushes the boundaries of the action genre by incorporating larger battlefields than ever before and players will experience conflicts that seamlessly span land, sea and space."
This is Halo, not Battlefield.
That is all.