There is an article I read where they mention Rivian execs told them the truck was I assume the SUV is almost the same.I'd be interested in learning the answer to that question as well.
The new Range Rover, which seems roughly similar in shape as the Rivian, is a relatively slippery 0.30. It would be great if the R1S was near that, but I suspect that it will be higher up in the 0.35 - 0.45 range that is typical for SUVs.
Good find! I can see it at 0.3 or just above. They do brag about how they tried to optimize it, which given the (relative to other EVs) enormous cross-section surface area seems necessary for decent range.