Microsoft has unsurprisingly stated that Halo 4 will not be released on PC.
According to a Microsoft representative, ”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.”
Halo and Halo 2 were released on PC, with the latter being a Windows Live title that was controversially Vista-only. Since then, no Halo game was ported to PC.