Unlike Halo: Reach and Halo 3, there will not be a public beta for Halo 4.
“While we are testing Halo 4 code, gameplay, and systems at significant scale to get excellent data, input, and feedback, we are focused on polishing and shipping our experience for the duration of the year,” said 343 Industries franchise development director Frank O’Connor in a Halo bulletin (via VG247), “and splitting resources to manage and build a beta is not on our schedule.”
Halo 4 is due for Xbox 360 this holiday season.