Subnautica 2 is crossplay between PC (Steam, Epic, Microsoft Store) and Xbox Series X|S from day one, wired through Epic Online Services. There is no PlayStation version at the moment, so if you're trying to play with a friend on PS5 the short answer is "you can't yet". For everyone else, joining a friend's session takes about ten seconds when it works. When it doesn't, you usually end up staring at a "Failed to join" error and no obvious next step. Below is the actual flow plus the common things that break it.
The two ways to invite somebody
Subnautica 2 doesn't use Steam, Xbox, or Epic friends lists directly for matchmaking – those are convenient on each platform individually, but crossplay needs a common identity layer. That layer is Epic Online Services. So there are two flows depending on where your friends are:
Same platform, already platform-friends (PC ↔ PC or Xbox ↔ Xbox):
- One player picks Host Multiplayer from the main menu.
- The host opens the in-game Friends List.
- The host clicks Invite next to the player they want.
- The invitee gets a pop-up in-game and hits Accept.
Different platforms, or not platform-friends:
You need to add each other with friend codes first.
- From the main menu pick Join Friends.
- At the top of that screen there's a button to generate your friend code. Hit it – you'll get a short string.
- Send your friend code to the other player however you normally talk (Discord, text, whatever).
- They paste it into the same screen on their side. You're now linked inside Subnautica 2's EOS friend list, separate from Steam/Xbox friends.
- From there the host can invite via the in-game Friends List exactly like the same-platform case.
It feels like two systems because it is. One for "platform friends I already have", one for "people I want to play this specific game with across platforms". Most of the support tickets I've handled for similar EOS-backed games come down to people trying to use only the platform list when the other player is on a different platform.
When the invite just doesn't go through
The failure modes I've seen most, roughly in order of how often they bite:
You're using the wrong friends list. Steam friends list is not the Subnautica 2 friends list. Xbox friends list is not the Subnautica 2 friends list. Cross-platform = friend codes, full stop. Once you've gone through the code dance, the friend appears inside the in-game Friends List, not in your Steam overlay.
One of you isn't on the latest patch. Subnautica 2 is in Early Access with frequent patches. Multiplayer protocol changes occasionally, and if one of you is a build behind, joins silently fail. Force-update through your store of choice on both sides, then retry.
EOS is down. Epic Online Services has had outages here and there over the last year. If joining a session is failing for everyone at once on every platform, check Epic's status page before tearing apart your own setup. It's rare but it happens.
Strict NAT on the host. Because the multiplayer is peer-to-peer, the host has to be reachable. If the host is behind carrier-grade NAT (common on mobile hotspots and some apartment-building connections), people can sometimes connect and sometimes not. Test by having the host's nearest friend join first – if even they can't, the host's network is the suspect. Fixes: wired instead of Wi-Fi, restart the router, switch off mobile hotspot. The proper fix is dedicated servers, which don't exist yet for Subnautica 2.
Game Pass cross-store mismatch. If you have the Microsoft Store / Game Pass version and your friend is on Steam, both should still see each other through EOS – but the in-game friend code flow is what unifies them. Don't expect the Steam overlay to know about your Game Pass friend.
The host's session went to sleep. If the host alt-tabs and their PC sleeps, the session goes with it. Sounds obvious. Comes up surprisingly often.
Hosts disappearing mid-game
If the host crashes, leaves, or their PC sleeps, the rest of the group is dropped. There's no host migration in Subnautica 2 right now – whoever was hosting was the only one with the world save. To pick up where you left off, the same host needs to come back online and re-launch, and everyone else re-joins through the Friends List. If the host can't come back (internet down, at work, on holiday), nobody else can play that world until they're back.
This is the strongest argument for dedicated server hosting once it exists. A real server doesn't sleep, doesn't have a Wi-Fi blip, doesn't go to work, and doesn't depend on one person's hardware. We'll have a product for that the moment Unknown Worlds ship the tooling.
Until then: keep the host wired, both players on the latest patch, friend codes for crossplay groups, and back the save up regularly (the save backup KB covers that in detail).