This is the Omega variant of the XR-54 Redeemer Medium Battle Armor. <da:thumb id="428990191">
However, Omegas are on a completely different level. They have been created using similar technology to the Praetorian Gears, and because of that, they can switch between several forms. This is the ultimate form of the Redeemer Omega.
The main difference between Omegas and Praetorians Gears, is that Omegas are advanced versions of the EXO armors.
The 11th Executioner Squad will also acquire one of these mighty armors later on in the story.