It looks like Unknown Worlds is posting sneaky screenshots of Subnautica 2 in the original game.
Whilst Unknown Worlds is being, ahem, coi, eagle-eyed fans think they've discovered sneaky peeks of Subnautica 2 in the first (and currently only) game via its time capsule feature.
Originally it wasn't clear where these mysterious images were coming from, but moderators of the Subnautica subreddit have since confirmed "screenshot[s are] from the upcoming Subnautica 2" and not fan-made mods.