There are eight different specializations in Halo 4, each of which has their own special armor set to unlock.
Unlocking these specialization armor sets is pretty straight forward in that you just need to level up the specialization to rank 10 to unlock the armor for that specialization.
Here is the list of specializations, and their unlockable armor matches the name as well.
Unlockable Specialization Armor Sets
Engineer Armor — Earn all ten ranks all ten ranks in the Engineer Specialization
Operator Armor — Earn all ten ranks in the Operator Specialization
Pathfinder Armor — Earn all ten ranks in the Pathfinder Specialization
Pioneer Armor — Earn all ten ranks in the Pioneer Specialization
Rogue Armor — Earn all ten ranks in the Rogue Specialization
Stalker Armor — Earn all ten ranks in the Stalker Specialization
Tracker Armor — Earn all ten ranks in the Tracker Specialization
Wetwork Armor — Earn all ten ranks in the Wetwork Specialization
Check out my complete guide for unlocking armor sets in Halo 4 if you’re looking for more armor to unlock.