To join the Experimental branch on Xbox, you'll need to meet the Xbox Insider Program requirements:
1. Be 18 or older (based on the birth date on your Microsoft account — this is required to accept the Xbox Insider Program Terms of Use).
2. Own Subnautica 2 or have an active Game Pass Ultimate subscription.
3. Have the Xbox Insider Hub app installed on your Xbox console or PC.
Once you've joined via the Xbox Insider Hub, you'll be able to opt in to the Subnautica 2 Experimental preview. The Experimental build installs alongside the stable version rather than replacing it, so you can keep both on your console and switch between them freely. You can leave the preview at any time to go back to playing only the default build.