Specialist — build your own class
The Specialist is the sequel's endgame answer to build freedom: an unlockable class that combines abilities from all five launch classes. Sources: official site, AvP Galaxy, AvP Central.
What the Specialist is
The official site describes the lineup as "five unique classes with major upgrades, plus a new Specialist endgame class for fully custom Marines" (official site). AvP Galaxy's first look confirms the mechanic: the Specialist lets you mix and match major and minor abilities from every available class — a build-your-own-class system rather than a seventh archetype.
Why it's an endgame class
The Specialist is unlockable (official site) and presumes you already know what each class's abilities do — its power is combinatorial. It's the destination of the progression loop: once your account has seen the five classes' kits, the Specialist lets you reassemble them around one playstyle.
What to combine (theorycraft with sources)
The best-documented ability pieces to covet for a Specialist build: the Medic's Guardian Kit (20 temp HP / 20% damage reduction, GamingBolt) for sustain, and the Hunter's Stasis Bolt / Particle Pulse pairing (GamingBolt) for priority kills. Add ordnance from the Marauder lane for wave clear and you have the classic "unkillable point-defense" fantasy. Exact combination rules will be updated here once verified in-game.
Track it
More detail lives on the Specialist hub, and every official video about the class is collected in the video library.
Sources: official site, AvP Galaxy — Specialist first look, AvP Central — classes, GamingBolt, GamingBolt.