Job listings for positions at Pitbull reveal the studio is "working on Unreal Engine 4 with Epic Games," but also, "games derived from that and Unreal Engine 3." Positions range from environment artists to engine programmers, with a variety of other roles in between. Epic confirmed the work with Joystiq this afternoon, and offered a prepared statement from director of engineering, Daniel Vogel. "Epic has a great history working with Pitbull Studio. We can count on them to provide reliable engineering resources, and they're helping us prepare for the next generation of games."
We'll see more from Epic's next-gen engine this June.