WildStar will be updated later today with patch v1.7.2 that brings Prime Raids into the game. Prime Raids give players incentive to return to older raid tiers. Prime Raids begin at Prime Level 1 that are similar to existing raid progression, but with a twist. Each raid and Prime Level beyond 1 increases the challenges and rewards over "normal" raiding.
Y-83 Prime Level 1 is the first tier of this new system and is specifically for organized groups that have progressed through normal raiding and are geared well enough to move through. After 1.7.2, additional raid dungeons will be released at Prime Level 1 until all have this version. The next update will start the Prime Level 2 iteration and so on.
Prime Level 1 raid dungeons can become even more challenging for the brave of heart by adding the Hard Mode designation on top of it. This buffs boss health and damage and includes new mechanics. This raises the number of difficulty levels for any given raid to normal, Prime Level 1, Hard Mode and Prime Level 1 Hard Mode.
Of course, great risk means great reward. The more difficult the encounter, the better gear and item drops players have a chance to earn, though these have not been specifically detailed in the post.
You can check out the details on the WildStar site.