Prime Titans are cosmetic DLC available in Titanfall 2, acting reskins of the default six Titans. They cannot be earned in-game and must be bought with real money - but do not have any changes or differences compared to their base-game counterparts. They instead have new textures, animations, sounds, Titan OS voices and new Termination animations.
Prime Titans were not available at Titanfall 2's launch and were instead added through staggered updates, these being Angel City's Most Wanted, Colony Reborn and Monarch's Reign (or, every other update). Two Titans were released in each update, in the order of Scorch Prime and Ion Prime, Northstar Prime and Legion Prime & finally, Tone Prime and Ronin Prime.
Prime Titans do not come with different weapons with the exception of Ronin Prime's Broadsword, which is retextured to look slimmer.