Fallout 76

Fallout 76 (game_id = fallout76) is one of the five Bethesda Creation Engine titles modde ships with. It shares the Bethesda deploy strategy, archive format, and INI machinery with Skyrim SE/AE, Fallout 4, and Starfield, but it is the odd one out: it is an always-online game whose saves live on Bethesda’s servers, and whose loose-archive mods are activated through an INI line rather than a local plugins.txt. Because of that, modde marks the title Partial overall, with Partial save tracking in particular.

Honest status: deployment, BA2 scanning, conflict classification, and launcher integration are real and working. What is not fully solved is save tracking (saves are server-side; only a local cache is visible) and load-order parity with single-player Bethesda games (Fallout 76 has no LOOT masterlist equivalent). See Supported games and the parity reference for the canonical status baseline.

Engine and overall status

The game is registered in crates/modde-games/src/registry.rs with the Bethesda engine family, the shared Bethesda collision classifier, a Fallout-76-specific archive scanner, and a Bethesda save tracker tagged as “FO76”. The plugin metadata lives in crates/modde-games/src/bethesda/mod.rs as the FALLOUT76 BethesdaGame record.

How modde detects the install

modde locates Fallout 76 the same way it finds every other Bethesda title: by its launcher IDs. The registration carries:

• steam_app_id = "1151340"
• steam_dir = "Fallout76" (the folder under steamapps/common/)

There are no Heroic GOG or Epic IDs for Fallout 76 — it ships on Steam (and the Microsoft Store / Bethesda launcher, which modde does not detect). On Linux the Steam copy runs under Proton, so modde resolves both the install root and the per-game Proton prefix from the Steam App ID:

~/.local/share/Steam/steamapps/common/Fallout76/          # install root
~/.local/share/Steam/steamapps/compatdata/1151340/pfx/    # Proton prefix

The Proton prefix matters for two things modde reads under drive_c/.../AppData/Local/Fallout76/: the (largely unused for FO76) plugins.txt location and the My Games documents tree where the local save cache lands.

Mod directory and deploy strategy

Like all Bethesda games, the mod directory is Data/ under the install root:

~/.local/share/Steam/steamapps/common/Fallout76/Data/

mod_directory() for the Bethesda plugin returns install.join("Data"), so modde deploys mod files into Data/ through its virtual-filesystem symlink farm — the same overlay mechanism used for every game. Your real Data/ directory stays clean; modde links the active profile’s files in and removes them on profile switch or undeploy. See the Deployment & VFS guide for how the overlay is built and torn down.

When modde extracts an archive whose contents look like a bare Bethesda layout (top-level meshes/, textures/, scripts/, interface/, sound/, strings/, … or loose .esp/.esm/.esl/.bsa/.ba2 files), it recognizes it as a Data-rooted mod and lays it down accordingly. This is the BareLayoutPolicy shared across Bethesda titles and is case-insensitive.

What scanning finds

Fallout 76 uses a dedicated scanner that differs from the Skyrim/Fallout 4 scanner. The single-player Bethesda scanner walks plugins.txt for an authoritative load order; Fallout 76 has no meaningful local load order, so it uses BethesdaArchiveScanner instead.

The Fallout 76 scanner (FALLOUT76_SCANNER):

• scans the Data/ directory only;
• discovers loose .ba2 archive files (the Fallout 76 archive extension);
• skips game-shipped archives by ignoring any file whose name starts with the SeventySix prefix (those are vanilla content, not mods);
• assigns each discovered archive a mod id of the form archive/<stem> and a confidence of 0.8 (a heuristic match, since there is no load-order file to corroborate it);
• maps a mod id back to its on-disk footprint as data/<stem>.ba2, which lets modde detect stale duplicates and reconcile a scanned archive against a managed mod.

In short: scanning Fallout 76 returns the loose .ba2 mods you have dropped in Data/, excluding Bethesda’s own SeventySix*.ba2 archives. Unlike Skyrim or Fallout 4, it does not pair plugins with companion archives or read enabled state from a load-order file, because Fallout 76 mods are activated through the INI rather than a plugin list. See the Scanning guide for the general scan workflow.

Conflict classification

Fallout 76 uses the shared Bethesda collision classifier, the same one used by Skyrim and Fallout 4. modde indexes the contents of .bsa/.ba2 archives (via the archive index reader) and classifies a file collision by its extension:

So two mods that both overwrite a texture inside their .ba2 archives produce a Cosmetic collision (last-deployed wins, cosmetically), whereas two mods that ship the same script or plugin produce a Dangerous collision worth your attention. The classifier reads inside archives, so it can flag conflicts between the contents of two .ba2 files, not just same-named archives.

Caveat for Fallout 76 specifically: Bethesda actively detects and bans certain client modifications in the online game. modde’s conflict severity is about file overwrites, not about whether a given mod is permitted online. Treat Dangerous-class mods (loose scripts, DLLs, plugins) with extra care on an online title.

See the Conflicts & load order guide for how severities surface and how overwrite order is resolved.

Save tracking

This is where Fallout 76 differs most from its single-player siblings, and why its save tracking is Partial.

Fallout 76 is an online game: the authoritative save is on Bethesda’s servers. The local .sav/.ess-style files in the Proton prefix are at best a partial cache, not your real character. modde represents this honestly:

• The Fallout 76 save tracker uses the magic header FO76_SAVEGAME to identify local Bethesda save files (the same binary header family as Skyrim’s TESV_SAVEGAME and Fallout 4’s FO4_SAVEGAME).

• When a save header parses, modde fingerprints the save number (a unique, incrementing slot id) and the player name read from the header.

• The tracker is flagged is_fo76 = true, so every capture is labelled with an explicit warning. Instead of the normal capture: … prefix, Fallout 76 captures read:

  capture (FO76 cache — server saves not tracked): …
  

That warning is the whole point: modde will fingerprint and snapshot what is on disk, but it tells you plainly that this is a local cache and that your real progress lives server-side and is not under modde’s control. The save directory modde looks in is resolved from the Proton prefix:

.../compatdata/1151340/pfx/drive_c/Users/steamuser/Documents/My Games/Fallout 76/Saves

(my_games_dir = "Fallout 76" for this title.) Do not rely on modde save profiles to roll a Fallout 76 character back and forth the way you would for Skyrim — the server state will not follow. For the general save-vault model (git-backed vaults, fingerprints, auto-capture), see the Save management guide.

Plugins and load order

has_plugin_system() returns true for every Bethesda game, and modde knows the Fallout 76 INI files it manages per profile:

• Fallout76.ini
• Fallout76Prefs.ini
• Fallout76Custom.ini

But in practice Fallout 76 has no plugins.txt-driven load order parity with single-player Bethesda titles. There is no LOOT masterlist for Fallout 76, and the game does not consume a plugins.txt the way Skyrim and Fallout 4 do. Instead, loose .ba2 archives are activated by listing them in the sResourceArchive2List / custom archive lines of Fallout76Custom.ini. That is why the scanner is archive-based rather than plugin-based, and why you should think in terms of “which archives are listed in my custom INI” rather than “what is my load order”. modde manages the INI files as part of a profile; you edit the archive list there to enable a loose .ba2 mod.

Installers (FOMOD, BA2, and friends)

Fallout 76 mods come in two common shapes, and modde handles both:

• Loose / archived files (.ba2 or bare Data/ layouts). Drop-in mods are recognized by the Bethesda bare-layout policy and deployed into Data/. A single .ba2 is the canonical Fallout 76 mod unit.
• FOMOD installers. modde includes a FOMOD engine (re-exported from fomod-oxide) shared by all Bethesda titles, so a Fallout 76 mod packaged as a FOMOD with ModuleConfig.xml is installed through the same interactive or declarative flow as a Skyrim FOMOD. See the FOMOD installer guide.

There is no REDmod, pak, or SMAPI handling here — those belong to Cyberpunk 2077, Unreal titles, and Stardew Valley respectively. Fallout 76 is archive-and-INI, plus FOMOD packaging.

Gaming tools for this title

Fallout 76 carries no built-in OptiScaler profile in its registration (optiscaler_profiles is empty) — unlike Stellar Blade, which ships a community-dxgi preset. You can still attach the generic tools modde supports to a Fallout 76 profile through the home-manager module or modde tool commands:

The most relevant of these for an online Proton title is proton itself, for runtime selection and DLL overrides. See the Tools & overlays guide for how tools attach to a profile and the Playing a game guide for the deploy-launch-capture flow.

Linux and Proton notes / known gotchas

The prefix-specific points here describe the game’s runtime on Linux and macOS, where Fallout 76 runs through Proton/Wine. On Windows the game runs natively, so there is no Wine prefix and the local cache and INI files live at their native Windows locations. modde itself runs natively on all three platforms.

• Always-online; saves are server-side. This is the single biggest gotcha. modde can snapshot the local cache but cannot version your real character. Every Fallout 76 capture is labelled FO76 cache — server saves not tracked.
• Anti-cheat / bannable mods. Bethesda enforces what is allowed in the live game. modde’s Dangerous severity flags file risk, not online-policy risk; loose scripts/DLLs/plugins can get you actioned regardless of how modde classifies the overwrite. Mod conservatively on a live online account.
• Activation is via Fallout76Custom.ini, not a load order. If a .ba2 mod does nothing after deploy, confirm its archive name is listed in the custom INI’s archive list — there is no plugins.txt to enable it.
• Vanilla archives are skipped on scan. Anything named SeventySix* is treated as base-game content and excluded from discovery, so it will not show up as a “mod”.
• No Heroic path. Detection is Steam-only for this title; there are no GOG or Epic launcher IDs.

Worked example

Home-Manager profile

A minimal Fallout 76 profile. Because saves are server-side, there is little point in elaborate save automation here — keep the profile focused on deploying loose-archive mods and selecting a Proton runtime:

programs.modde = {
  enable = true;
  nexus.apiKeyFile = "/run/secrets/nexus-api-key";

  profiles.fo76 = {
    game = "fallout76";
    installMode = "auto";
    gameDir = "/home/me/.local/share/Steam/steamapps/common/Fallout76";

    tools = {
      proton.enable = true;
      gamemode.enable = true;
      mangohud.enable = true;
    };
  };
};

CLI

# Confirm modde sees the install (Steam App ID 1151340).
modde game list

# Scan Data/ for loose .ba2 mods (skips SeventySix* vanilla archives).
modde scan --game fallout76

# Inspect conflicts between deployed archives' contents.
modde conflicts --game fallout76

# Deploy the active profile's mods into Data/ and launch under Proton.
modde play --game fallout76

# Snapshot the local save cache. Note the FO76 server-side warning in output.
modde save auto-capture --game fallout76

modde save auto-capture --game fallout76 will print a capture line prefixed with capture (FO76 cache — server saves not tracked), reflecting that the real character lives on Bethesda’s servers.

See also

• Supported games — the canonical status table
• Fallout 4 and Starfield — sibling Creation Engine titles with full single-player save tracking
• Deployment & VFS
• Mod scanning
• Conflicts & load order
• Save management
• FOMOD installer
• Tools & overlays
• Playing a game
• Parity reference