Last year, Boston Dynamics and DARPA showed off Cheetah on a track running with all the cables. This time, Boston Dynamics introduces WildCat. In my opinion, it is like the hybrid of their LS3 and Cheetah.
In the demonstration, it is using a small fuel tank that can sustain for 5 minutes. BTW, it is using a Go Kart engine on this WildCat. Here is the video. Very impressive.