With ambitious production targets and fresh off a $700 million investment led by Amazon, one would think electric car manufacturer Rivian would be testing dozens of prototypes across the United States. Yet virtually none have been spotted.

There’s a good reason for this: they’ve been hiding in plain sight.

Talking to the Detroit Free Press in a wide-ranging interview, Rivian chief executive R.J. Scaringe revealed that the company is testing its electric skateboard architecture under the shells of Ford F-150s.

According to Scaringe, there’s no corporate connection between Rivian and Ford and the F-150 was selected because it just happens to have virtually the same wheelbase as the upcoming R1T pickup and R1S SUV.

“We need something to keep the weather out while we put a lot of miles on our skateboard, so they’re driving around in Detroit right now, too. They’re all over the place, but nobody knows. We’re very quiet about that,” he said.

Unlike many of its rivals bursting onto the electric vehicle scene, Rivian is very open about the fact that development of its vehicles is still in its early stages. Scaringe says the firm would rather under promise and over deliver than over promise and under deliver.

“Part of our culture, part of what I’ve worked really hard to embed is a level of humility and honesty with how hard this is. Very often not just … for new automotive companies but also for startups in general … there’s the desire to present what you’re working on as being far more complete than it is so that the (perceived) progress is 10 times the real progress. We try to achieve the opposite of that.”

This philosophy appears to be working for Rivian as it’s been the talk of the town since the R1T and R1S were unveiled at the Los Angeles Auto Show.