Subnautica 2

Subnautica 2 (game_id = subnautica2) is one of modde’s Unreal Engine titles. It shares the data-driven UE4 plugin with Stellar Blade and Oblivion Remastered: a single Ue4Game definition parameterised per title, with the trait implementation reused across every Unreal game. Its overall status is Partial — the engine path (detection, deployment, conflict classification, save tracking, Wine/Proton DLL overrides) is wired and shipped, but there is no bespoke Subnautica-specific scanner, save format parser, or mod-loader integration beyond the generic pak layout. Treat it as “the UE4 pipeline pointed at Subnautica 2”, not a hand-tuned per-game experience.

Status baseline. The authoritative per-game status lives in Supported games and in docs/capability-matrix.toml. This page expands on the engine mechanics; it does not change the status.

Engine and overall status

The Unreal4 engine family is modde’s umbrella for Unreal pak/IoStore games regardless of whether the title is technically UE4 or UE5 — the on-disk layout (<Project>/Content/Paks/, <Project>/Binaries/Win64/, ~mods mount ordering, pak/ucas/utoc chunk triples) is the same, so the same code path drives both.

How modde detects the install

Subnautica 2 is registered with Steam launcher IDs only:

Detection walks your Steam libraries (parsed from libraryfolders.vdf, so extra drives are covered) and looks for steamapps/common/Subnautica2. There is no Heroic (GOG/Epic) mapping for this title today, so a non-Steam copy must be pointed at explicitly with --game-dir (CLI) or gameDir (home-manager). Run modde detect to see what modde resolves before you commit a profile to it.

The install root is the directory that contains the UE project folder Subnautica2/. modde derives everything else from there:

• Paks root: <install>/Subnautica2/Content/Paks
• Executable / proxy-DLL dir: <install>/Subnautica2/Binaries/Win64

Proton prefix

Saves and per-user config live inside the Proton prefix Steam creates for App ID 1962700, not in the install directory. modde resolves the prefix as <steam_library>/steamapps/compatdata/1962700/pfx. If you have never launched the game, that prefix does not exist yet and modde’s save/config resolution returns nothing — the fix is to launch Subnautica 2 once through Steam (Proton) so the prefix is created, then re-run modde.

Mod directory and deploy strategy

modde deploys mods into the tilde-prefixed ~mods folder under the paks root:

<install>/Subnautica2/Content/Paks/~mods/

The leading tilde is deliberate: Unreal’s pak mounter loads ~mods after the shipping paks, so modded content overrides base game content rather than the other way around. modde creates this directory if it does not exist.

Deployment uses modde’s standard staging-and-link model (see Deployment): mods live in per-mod staging directories, and the active profile is materialised into ~mods by linking the enabled mods’ files. A pak/ucas/utoc triple that shares a file stem is treated as one logical mod — the IoStore container (.ucas/.utoc) and its .pak header travel together.

When modde analyses a downloaded archive, it recognises the Subnautica 2 layout when the archive root contains at least one .pak, .ucas, or .utoc file and classifies it as a single file set (InstallMethod::SingleFileSet) — i.e. “drop these chunk files into ~mods”. Archives that do not present pak files at their root fall through to the generic installer flow.

What scanning finds

modde scan --game subnautica2 walks two directories under the paks root and groups .pak/.ucas/.utoc files by file stem into discovered mods:

LogicMods is included because UE4SS-style Blueprint/logic mods conventionally ship there; modde reports anything it finds in that folder even though it deploys its own managed mods into ~mods. Each discovered mod gets an ID of the form pak/<stem> and is recorded at a confidence of 0.9. Sibling .ucas/.utoc files collapse into the same row as their .pak (the footprint is represented by subnautica2/content/paks/~mods/<stem>.pak), so a multi-chunk mod shows up once rather than three times.

Scanning is filesystem discovery only — it tells you which pak sets are physically present. It does not parse pak contents, read UE asset trees, or resolve load-order semantics. See Scanning for how discovered rows reconcile with manifest-driven installs.

Conflict classification

Conflicts are classified by the shared UE4 collision policy. Two mods “collide” when they ship a file at the same relative path; the severity of that overlap is decided by file extension:

The archive extensions that participate in pak-aware collision handling are pak, ucas, and utoc. Because Subnautica 2 mods are predominantly pak sets, most real conflicts you will see are Dangerous same-path pak overlaps: two mods both shipping, say, ~mods/zMyOverhaul.pak cannot coexist without one shadowing the other. modde surfaces these so you can choose a winner via load order / filename prefixing rather than discovering it in-game. See Conflicts for the full classification model and how to resolve overlaps.

Save tracking

Save tracking is shipped (Done) and Subnautica 2 opts into modde’s per-profile save layer (supports_save_profiles = true).

Location

modde resolves the save directory inside the Proton prefix:

<steam_library>/steamapps/compatdata/1962700/pfx/drive_c/users/steamuser/
  AppData/Local/Subnautica2/Saved/SaveGames

If the prefix does not exist yet (game never launched), save resolution returns nothing — launch once through Proton first.

What is captured and fingerprinted

The UE4 save tracker is a pattern tracker that recursively matches *.sav files under the save directory, labels each by its file stem, and files them under the manual category. “Recursive” matters for Subnautica 2 because UE titles often nest per-slot save folders; modde descends into them.

Captured saves are committed into a per-game git vault (one repository per game_id, one branch per profile), which gives history, branching, and rollback for free. Each capture commit also records a mod fingerprint:

• The fingerprint is a SHA-256 over the sorted, de-duplicated list of enabled, save-breaking mod IDs in the active profile.
• A mod is “save-breaking” if it ships any of the save-affecting extensions pak, ucas, utoc, dll, or lua — i.e. exactly the content types that can change game logic. Purely cosmetic mods (png, jpg, dds, tga, ini) do not move the fingerprint, so two profiles that differ only in textures stay compatible.
• The fingerprint and a human-readable mod list are stored as Mod-Fingerprint: / Save-Breaking-Mods: git trailers on the capture commit.

When you later restore a snapshot, modde compares the stored fingerprint against the current profile and warns if the save-breaking mod set has changed (which mods were added/removed), so you do not silently load a save into an incompatible mod configuration. See Saves for the capture/restore/rollback workflow.

Note: the file content itself is not hashed — the fingerprint identifies the mod configuration that produced the save, not the bytes of the save file.

Per-user config deploy target

Beyond saves, the UE4 plugin exposes one deploy target for user-editable config:

This lets modde place INI tweaks into the prefix’s Saved/Config/Windows directory. As with saves, the target resolves to nothing until the Proton prefix exists.

Plugin and load-order handling

Unreal pak games have no plugins.txt-style master/plugin list the way Bethesda titles do. Load order is filename/mount order within ~mods: paks mount in a deterministic order, and ~mods mounts after the base paks. There is no Subnautica 2 load-order editor in modde; if two pak sets conflict, you resolve it by choosing which mod wins (renaming with a sorting prefix, or disabling one). modde’s job here is to make the conflict visible and the deployment reproducible — not to arbitrate UE pak precedence automatically.

Installer specifics

Subnautica 2 mods are pak-based, so there is no FOMOD/REDmod/SMAPI flow specific to this title:

• Pak sets are the native format. modde’s archive analysis detects a root-level .pak/.ucas/.utoc and deploys the set into ~mods.
• FOMOD installers are still supported generically (the FOMOD engine is engine-agnostic), but most Subnautica 2 mods are plain pak archives that need no scripted installer. See FOMOD installers if you do hit one.
• No REDmod / no SMAPI / no Bethesda plugin tooling applies here — those belong to Cyberpunk and Stardew/Creation-Engine titles respectively.

Gaming tools that matter

modde manages external gaming tools per game (see Tools). For Subnautica 2:

• Proton is the runtime. modde’s proton tool selects the Proton build and can apply DLL overrides; everything below the executable runs inside the App ID 1962700 prefix.

• Wine DLL overrides for proxy DLLs. UE mod loaders (UE4SS) and overlays ship as proxy DLLs that must be loaded as native instead of Wine’s built-in stub. modde scans Subnautica2/Binaries/Win64/ (or a mod’s staging dir) for known proxies and emits the right WINEDLLOVERRIDES. The recognised proxy DLLs are:

  Proxy DLL	Typical use
  dwmapi	UE4SS default proxy
  xinput1_3	UE4SS alternate / some trainers
  d3d11	ReShade / ENB-style
  dxgi	ReShade / DLSS swappers
  version	Generic ASI loader
  winmm	Generic ASI loader
  dinput8	Generic hook

• No OptiScaler profile ships for Subnautica 2. Unlike Stellar Blade — which has a community-tested community-dxgi OptiScaler preset — subnautica2 registers an empty OptiScaler profile list. You can still enable the generic optiscaler tool if you know what you are doing, but modde provides no curated, game-specific preset for this title, so there is no profile = "..." value to select. Overlays like MangoHud, VkBasalt, and GameMode are engine-agnostic and work as for any Proton title.

Linux / Proton notes and gotchas

These notes cover the game’s runtime on Linux and macOS, where Subnautica 2 runs through Proton/Wine. On Windows the game runs natively — there is no Wine prefix, and saves and per-user config live at their native Windows locations. modde itself runs natively on all three platforms.

• Launch once before modding state resolves. Saves, the ue4-saved-config target, and prefix-based config all require the Proton prefix to exist. A fresh install has no compatdata/1962700 until you run the game once.
• ~mods lives in the install, saves live in the prefix. These are two different trees on disk. Deploy/scan operate on <install>/Subnautica2/Content/Paks; save capture operates on the prefix. Do not look for saves under the install directory.
• IoStore triples must stay together. Deploying or removing a .pak without its .ucas/.utoc (or vice versa) produces a broken mount. modde groups them by stem, so let modde manage the set rather than hand-copying single files.
• Browse Nexus picker. Subnautica 2 has a Nexus domain (subnautica2) but no numeric Nexus game ID recorded, so URL-based installs and update tracking work while the UI’s “Browse Nexus” game picker may hide the title until the numeric ID is confirmed. You can still install from a nexusmods.com/subnautica2/mods/<id> URL or nxm:// link.
• Verify your runtime against the game’s current state. Subnautica 2 is an evolving title; pak mods can break across game patches. Capture a save before a big mod change so the fingerprint lets you roll back cleanly.

Worked example

Home-Manager profile

A minimal declarative Subnautica 2 profile. Point gameDir at the Steam install (the directory containing Subnautica2/), and let activation manage the rest.

programs.modde = {
  enable = true;

  profiles.subnautica2-modded = {
    game = "subnautica2";
    installMode = "auto";
    gameDir =
      "/home/me/.local/share/Steam/steamapps/common/Subnautica2";

    tools = {
      # Engine-agnostic overlays work fine on this Proton title.
      mangohud.enable = true;
      gamemode.enable = true;
      # No OptiScaler preset ships for subnautica2, so there is no
      # `profile = "..."` to set here.
    };
  };
};

If the game is not installed yet, omit gameDir or set installMode = "await-game"; activation prints the next step instead of failing. See the Home-Manager module reference for every option.

CLI

# See what modde resolves for the install and Proton prefix.
modde detect

# Create a profile and scan the pak directories for existing mods.
modde profile create modded --game subnautica2
modde scan --game subnautica2 --import-to modded

# Install a pak mod from a Nexus URL into the profile.
modde install mod "https://www.nexusmods.com/subnautica2/mods/123" \
  --profile modded

# Deploy the active profile's mods into Content/Paks/~mods.
modde deploy --game subnautica2 --profile modded

# Switch profile, deploy, capture the outgoing profile's saves, and launch.
modde play modded --game subnautica2

If your copy is not a default Steam install, add --game-dir <path> to the commands that take it (scan, deploy), pointing at the directory that contains Subnautica2/.

Named executables (modding tools)

modde can manage named launch targets — UE4SS-driven tools, trainers, or any helper executable — with overwrite capture, custom working dir, environment, and Wine DLL overrides. The exec commands are a thin alias for the executable subset of tool; the two share storage.

# Register a tool as a named launch target for subnautica2.
modde exec add my-tool "/path/to/Tool.exe" --game subnautica2 \
  --wine-dll-overrides "dinput8=n,b" \
  --env "SOME_VAR=1" \
  -- --tool-arg value

# Equivalent via the tool surface:
modde tool add-executable my-tool "/path/to/Tool.exe" --game subnautica2

# Run it, capturing any files it writes into the overwrite mod.
modde exec run my-tool --game subnautica2 --profile modded

Captured output defaults to the __overwrite__ mod; pass --output-mod <name> to route writes into a named mod instead. See Tools and Playing for the full launch model.

See also

• Supported games — the canonical status table and per-game guide index
• Stellar Blade — sibling Unreal title (has an OptiScaler preset)
• Oblivion Remastered — another Unreal4 pak title
• Deployment — staging-and-link deployment model
• Scanning — filesystem discovery and manifest reconciliation
• Conflicts — collision classification and resolution
• Saves — capture, fingerprints, restore, and rollback
• Tools — Proton, overlays, and named executables
• Playing — switch-deploy-capture-launch flow
• Home-Manager module — declarative profile options
• Parity reference — how modde’s coverage maps to MO2/Vortex