We've seen it from a couple of weird angles, but now it's finally revealed in its entirety by Unbox Therapy:
Apparently gets incredible battery life
We already know that it is IP68-verified, which in turn means dust and water protection (1.5 meters for 30 minutes), a week of battery life is very nice and makes up for the design that is very reminiscent of Samsung Galaxy Watch Active .
OnePlus loves fast charging, so it takes amazingly no more than 20 minutes to fully charge it (and then be able to use it for a week!). The watch will also be a remote control for OnePlus TV, and has 4GB of storage.
This was revealed by OnePlus before the press conference: