Hiding beneath the exterior is the bones of a Rivian R1T electric pickup truck. Apparently, there are dozens of these trucks out testing in and around Detroit.
Rivian has selected the F-150 because it doesn't stand out (it's the #1 selling truck in the U.S.) Since the F-150 is such a common sight, few would think twice upon seeing one on the roads. That makes it a perfect donor vehicle for testing the upcoming Rivian R1T out in the real world.
We've seen a plug-in Ford F-150 too, but that's a Ford project that is unrelated to Rivian.
So, keep your eyes peeled for these plug-in F-150s. There are two types, one of which is not a Ford, but both are electric trucks.