Modding Subnautica 2 with Hydro

Subnautica 2 launches into Early Access on May 14. Hydro is the modding platform built for it.

Subnautica 1 had a strong modding scene built on tools like BepInEx and QModManager. Both were built for Unity. Subnautica 2 runs on Unreal Engine 5, and that toolchain doesn't load on it. Anyone modding SN2 needs different tools. Hydro is the rebuild for UE5.

How it works

The Hydro launcher detects your Subnautica 2 install on Steam, Epic, or Game Pass automatically. Browse mods at hydrosx.com, click install, launch the game from the launcher, and mods load. No file copying, no config editing, no manual injection.

Each install is verified with SHA-256 before it runs. Profiles let you keep different mod loadouts for different saves, and you can disable a mod without uninstalling it.

Day one mods

Five quality-of-life mods are available at launch: skip intro logos, FOV slider, XYZ coordinates on the HUD, a hotkey to toggle the HUD, and motion blur off. Anything that adds gameplay content like new creatures or biomes needs the gameplay API, which comes after launch. The community will add more as the week goes on.

Built for Early Access

Subnautica 2 will patch often during Early Access, and most UE5 mod loaders need manual updates after each patch because they search for code patterns that shift when the game recompiles. HydroCore takes a different approach. It anchors on engine debug strings the developers wrote, things like "Unable to add more objects to disregard for GC pool", to find the engine systems it needs. Those strings stay stable across patches. The first launch caches the scan results, so subsequent launches are instant until an actual patch installs.

Mods keep working through patches. Modders do not have to chase every update.

Security

Every mod uploaded to Hydro goes through a five-stage scanning pipeline before it can be downloaded: file validation, manifest check, static analysis, ClamAV, and VirusTotal. Anything that fails any stage does not get listed.

The tier system enforces what mods can do at runtime. Tier 1 mods run in a Lua sandbox that prevents unsafe operations entirely. Tier 2 mods provide shared APIs other mods build on, in the same sandbox. Tier 3 native mods get unrestricted access for cases the sandbox cannot handle, and go through manual review before they can be published.

The code that loads into your game is open source. HydroCore is on GitHub at github.com/bmartin127/Hydro-Core under MIT. You can read every line that runs in your game process before installing anything.

For modders

Mods package as a single .hydromod file with a hydromod.toml manifest. Upload to hydrosx.com, the scanning pipeline runs, approved mods appear in the launcher's Discover tab. Hydro mods are written in Lua against the sandboxed API: generic engine access (Hydro.Assets, Hydro.World, Hydro.Events, Hydro.Reflect), pak mounting, AssetRegistry integration, and UObject reflection. The Tier 3 escape hatch exists for things Lua cannot do.

What comes after launch

Several things are next: multiplayer modpack sync via a .hpack format so co-op players auto-share mods on join, game-specific gameplay APIs for new creatures, biomes, items, and equipment, more day-one style quality-of-life mods, and native injection replacing the current UE4SS bootstrapper.