Today's dev vlog discusses multiplayer in Subnautica 2. The video is 4min and 27seconds.

Multiplayer will be an optional co-op mode. You'll be able to do everything solo, you won't be locked out of anything if you don't have another player helping you.

They did some work on making the swim animations look good, so when you see your friend swimming next to you, the motions will be fluid.

There's a "dive elevator" that multiple players can use simultaneously to go down quickly, load up with materials, then come back up.