Though we've already determined that the video is CGI and not real, we do know that Rivian intends to tout this ability with its upcoming R1T truck and R1S SUV. A true tank turn might not be entirely possible, but something very similar to one seems to be Rivian's intention.
It appears that Rivian has trademarked the term "Tank Steer" which makes an appearance in this video. It has also trademarked the similar term "Tank Turn." This is further evidence that turning on a dime (or close to it) will be a feature at least some Rivian vehicles will have.
Since we know Rivian Automotive's vehicles have incredible torque, gobs of power, otherworldly off-road capabilities, and highly advanced all-wheel-drive systems and state-of-the-art traction control, this type of maneuver is definitely possible.
Check out this new clip above to see the turn in more detail.
Video description via nextFutureTechs on YouTube:
Rivian Pickup Tank Steer Mode Detailed Zoom Review