Penny Arcade got the scoop from the rep, stating “Halo 4 was designed specifically for Xbox 360, and while we’re always exploring new ways to expand the franchise and share the Halo experience with as many fans as possible, we do not currently have any plans to port Halo 4 to PC.”
The last time a Halo game graced the PC was Halo 2, and before that, Halo: Combat Evolved.
Microsoft does have plans to expand its user base with PC in mind, but it looks like Halo 4 isn’t a part of that. Don’t hold your breath for the rest of the Halo Reclaimer Trilogy either.
Source: Game Spot