https://www.pcgamer.com/subnautica-below-zero-early-access-release-set-for-january-30/

Subnautica: Below Zero is a followup to last year's outstanding underwater sci-fi survival game, set in a different region of the same planet after the events of Subnautica. I won't get into that too much in order to avoid spoilers, but it means that Below Zero could be a good bit different from its predecessor in some ways.

One way it will not differ is how it's released: Subnautica made its debut on Steam Early Access in 2014 in a far-from-complete state, and Unknown Worlds said that Below Zero will follow the same path, beginning on January 30. It will be available in early access on Steam, the Epic Games Store, and Discord (not listed there yet), and it will not be ready for its closeup.