Well done to Secret Projects forum for spotting this nugget that everyone else missed. This stealthy looking model plane is Lockheed Martin's concept for what anext-generation super shot take-off and landing tactical airlifter would look like.
The four-engine plane (though I only see two in these pictures), called the Speed Agile Concept Demonstrator, is Lockheed's part of an Air Force Research Lab effort to develop designs for a STOL tactical transport jet capable of operating from short and unprepared landing strips around the world. Boeing is apparently also in on the effort.
The 23-percent scale model, equipped with Williams FJ-44 turbofan engines, is being tested in the world's largest wind tunnel at the Air Force's Arnold Engineering and Development Center to see how well the craft's hybrid powered lift design performs. Hybrid powered lift means the plane combines a low drag airframe with very simple mechanical assembly leading to reduced weight and better aerodynamics, according to the AFRL.
Steve Trimble at The DEW Line points out that the last time the Air Force moved to develop a STOL cargo jet it eventually ended up with the C-17 Globemaster -- a strategic airlifter that can land in some pretty tight spots.