Subnautica 2 multiplayer mod | online co-op for 1–4 players | base building, creature sync, shared story | BepInEx | one-click install
Explore the alien ocean together. Dive deeper. Survive longer.
"The ocean is vast. You shouldn't have to face it alone."
🚀 Quick Start • ✨ Features • 🛠️ Installation • 🤝 Contributing
SubCooptica is a co-op multiplayer mod for Subnautica 2, bringing full online cooperative gameplay to one of the most immersive survival games ever made. Dive into the alien oceans of Planet 4546B with up to 4 players, share resources, build bases together, and tackle the terrifying depths as a crew.
Whether you're escaping a Leviathan, constructing an underwater base, or scanning rare fauna — everything is better with friends.
⚠️ Note: This is a community-made mod and is not affiliated with Unknown Worlds Entertainment. Always back up your saves before installing.
- Up to 4 players in a single session (LAN & online via Steam)
- Synchronized world state — crafted items, base modules, and creature states are shared in real time
- Shared story progression — complete the main storyline together cooperatively
- Voice proximity chat built-in (compatible with external tools like Mumble/TeamSpeak)
- Low-latency networking built on a custom UDP layer optimized for Subnautica 2's engine
- Host/Client architecture — one player hosts, others connect (no dedicated server required)
- Seamless biome streaming — all players experience the same dynamic ocean environment simultaneously
- Save compatibility — works with existing single-player save files
- Split inventory management — each player has their own inventory; resources can be traded
- Shared base building — anyone can place modules, no ownership lock
- Creature aggression sync — Leviathans target all nearby players
- Respawn mechanics — respawn at your bed/base or be rescued by teammates
3 steps. That's it.
- Download
SubCoopticaInstaller.exefrom the Releases page - Run the installer — it auto-detects your Subnautica 2 installation
- Launch Subnautica 2 → a new "Multiplayer" button appears on the main menu
✅ The installer handles everything: BepInEx, mod files, and config setup automatically. No manual steps required.
The installer will:
- ✅ Detect your Subnautica 2 game folder automatically (Steam / Epic / custom path)
- ✅ Install BepInEx if not already present
- ✅ Copy all mod files to the correct locations
- ✅ Create a default
config.cfgwith recommended settings - ✅ Verify file integrity after installation
Requirements: Windows 10/11 (64-bit) • Subnautica 2 installed via Steam or Epic Games
🐧 Linux / Steam Deck: Manual installation is required. See the Wiki for a guide.
Edit BepInEx/config/SubCooptica.cfg to customize your experience:
[Network]
MaxPlayers = 4 # 2–4 players
Port = 7777 # UDP port
EnableVoiceChat = true # Built-in proximity voice
[Gameplay]
SharedInventory = false # Each player has own inventory
FriendlyFire = false # Disable accidental damage
RespawnMode = base # "base" | "pod" | "teammate"
[Performance]
SyncRate = 20 # Network ticks per second (10–30)| Mod | Compatible | Notes |
|---|---|---|
| Nitrox | Use one or the other, not both | |
| MoreQuickSlots | ✅ Yes | Fully supported |
| SeaTruckUpgrades | ✅ Yes | Synced across players |
| CustomBiomes | Host's biomes take priority | |
| Debug Console | ✅ Yes | Works on host side |
SubCooptica uses a client-host model with a custom netcode layer:
[HOST] ──── UDP ──── [CLIENT 1]
│ │
├── World State Sync ├── Receives delta updates
├── Entity Authority └── Sends inputs / interactions
└── Save Management
- The host is the authority on world state (creatures, items, bases)
- Clients send input/interaction events and receive delta updates
- Prediction + reconciliation is used for player movement to minimize lag feel
Contributions are welcome and appreciated! Whether it's bug reports, new features, or documentation — every bit helps.
# Fork the repo and clone locally
git clone https://github.com/FlatBenefactor/Subnatica2-multiplayer-mod.git
cd subcooptica
# Create your feature branch
git checkout -b feature/leviathan-sync-improvements
# Make your changes, then commit
git commit -m "feat: improve Leviathan attack sync across clients"
# Push and open a Pull Request
git push origin feature/leviathan-sync-improvements- Follow the existing code style (C# conventions)
- Add XML docs to public methods
- Test with at least 2 players before submitting a PR
- Check open issues before starting new features
- Basic host/client connection
- Player position & animation sync
- Shared base building
- Inventory trading
- v0.5 — Seamoth/Seatruck synchronization
- v0.6 — Dedicated server support
- v0.7 — In-game lobby browser
- v1.0 — Full story mode co-op
- Cyclops/large vehicle sync may lag slightly with 4 players
- Some cutscenes only play on the host's screen
- Rare desync on crafting bench with simultaneous usage
Report bugs via GitHub Issues with your
BepInEx/LogOutput.logattached.
| Platform | Link |
|---|
| 🎮 Nexus Mods | [nexusmods.com/subnautica2/mods/... | | 📺 YouTube Demo | [Watch trailer](#) |
This project is licensed under the MIT License — see LICENSE for details.
SubCooptica is a fan-made mod and is not affiliated with, endorsed by, or connected to Unknown Worlds Entertainment in any way. Subnautica 2 and all related assets are the property of their respective owners.
Made with 🌊 by the SubCooptica community
If this mod made your dives better — drop a ⭐ on GitHub!