Subnautica 2 supports up to four players in a single co-op session, including the host. The mode is optional, drop-in and drop-out, and built so that solo play remains the full experience.
Quick answer: The maximum player count in Subnautica 2 is four (one host plus three invited friends), with crossplay between PC and Xbox Series X|S.
Subnautica 2 player cap and session structure
A co-op session in Subnautica 2 holds a maximum of four players total. The host runs the world, and the other three slots are filled by invited friends. There is no larger party size, no public matchmaking lobby, and no local split-screen mode. Vanilla dedicated servers also use the same four-player cap.
Unknown Worlds designed the sequel with multiplayer in place from the start, but the game is balanced as a single-player title first. Every feature available in solo can be done in co-op, and nothing in the game requires a second player. There are no multiplayer-only puzzles or tandem-switch mechanics.
Co-op reference table
| Feature | Detail |
|---|---|
| Max players per session | 4 (host + 3) |
| Minimum players | 1 (full solo supported) |
| Session type | Host-led, drop-in / drop-out |
| Crossplay | PC (Steam, Epic) and Xbox Series X|S |
| Local split-screen | Not supported |
| Save conversion | Single-player save can be opened for co-op and reverted |
| Multiplayer-exclusive content | None |
| Dedicated server cap (vanilla) | 4 |
How to start a four-player session
Step 1: From the main menu, choose Host Multiplayer to open a world for friends, or pick Join Friends to enter someone else's session. The same menu lets you swap a session back to single player.
Step 2: If you are continuing an existing solo run, load the save and switch it to multiplayer from the same menu. No new save file is required, and you can return the world to solo later.
Step 3: Invite up to three players through the in-game friends list. PC and Xbox accounts both appear in the same list, so a mixed-platform group still totals four players.
Solo, co-op, and save behavior
The host's world is the only persistent world for the group. When the host stops playing, the other players cannot continue in that save on their own. Each player can, however, keep a separate personal save for solo runs, and a single-player save can be opened to co-op at any time without losing progress.
Shared progression inside a session covers things like scanned items in the data inventory, base construction, and crafting. Resources placed in shared storage are accessible to anyone in the world, so visiting friends can pick up materials that belong to the host.
Crossplay limits
Crossplay is enabled between Steam, Epic, and Xbox Series X|S at Early Access launch. PlayStation is not part of the launch lineup, so there is no PS5 crossplay at this stage. The four-player ceiling still applies regardless of how the group is split across PC and Xbox.
If you wanted larger lobbies, the sequel does not provide them, and a fifth player cannot join even with crossplay enabled. For groups of four or fewer, the design lets you mix solo and co-op freely on the same save without locking content behind the multiplayer mode.