Halo 4's online multiplayer components will feature a new way to differentiate your own Spartan from those used by the other seasoned warriors you'll be battling with over Xbox Live. Dubbed "Specializations" and available after reaching Level 50, Halo 4's version of character classes each feature nine levels of various unlockable cosmetic upgrades (outfits, armor and weapon skins, etc), capped off by a final tenth level that grants a class-specific ability.
There are eight different Specializations in total, two of which will be available to everyone as soon as the game launches on November 6: Wetworks, which allows the use of Promethean Vision without the usual drawbacks, as well as a quieter sprint, and Pioneer, which gains XP at an accelerated rate, provided that perk is active.

The other six Specializations (Engineer, Tracker, Rogue, Stalker, Patherfinder and Operator) will be gradually made available to players post launch, unless they preorder the Halo 4 Limited Edition, in which case all eight classes will be available from day one. Hit up that source link below for specifics on each Specialization and more pictures of weird space-bug helmets.