Fallout 4 AI NPC Mod: Talking Companions and Voice Commands

What does your companion say when you ask about something the writers never planned for? In vanilla Fallout 4, nothing at all. A Fallout 4 AI NPC mod built on Neocortex lets companions answer the player in their own words, turns settlement management into voice commands and adds a Vault-Tec quiz terminal to your favorite settlement. We start with what the player would experience, then get into F4SE runtimes, Papyrus and the plugin code.

Screenshot: Fallout 4 © Bethesda Softworks

Companions who answer back

Rebuild a companion's voice as a Neocortex character, or add a new one: a Personality type, an Emotion profile and a Knowledge base from a TXT file about their past and the factions they distrust. Your mod sends each player line to /v3/chat with recent events ("the player sided with the Brotherhood", "radstorm incoming") and nearby objects such as a locked door or a power armor station.

The companion answers in voice, played from /v3/audio/generate or /v3/audio/stream. Every line carries an emotion tag like ANGRY or CURIOUS for expressions, and actions like { "name": "OPEN_DOOR", "targetId": "door_02" } tell your mod what to do.

On Pro and Team plans, group chat lets up to six characters share one conversation, so a road trip with two companions and a caravan trader turns into an actual argument. A Conversation Flow can steer a personal quest through branching scenes: the companion opens up, asks for help, and each beat returns a checkpoint keyword (flowState) your Papyrus quest script turns into the next stage.

Run your settlements by voice

Settlement building is menu-heavy, which makes it the best place for voice. Design a command set with actors ("settlers", "Preston", "Dogmeat"), actions ("build", "go", "guard", "follow") and objects ("turret", "workshop", "the gate"). Players say "build a turret here" or "everyone to the workshop", and your mod receives clean commands, including several actions in one sentence and quantities like "post two guards at the gate".

It works push-to-talk or always-listening, offline, in multiple languages, using the Neocortex Voice Commands library on the player's machine, with no cloud round trip. Learn more in our guide to on-device voice commands for game mods. Voice Commands is a licensed SDK: contact us for a Voice Commands license.

A Vault-Tec aptitude test in Sanctuary

Place a terminal in Sanctuary that runs a Vault-Tec style aptitude test with a cheerful host voice. The question set lives in the Neocortex dashboard, and the quiz engine (Team plan) handles questions, scoring and a leaderboard through /v3/quiz. The player answers out loud through speech-to-text, and your mod hands out caps or a perk magazine for a high score.

Which F4SE build should you target?

F4SE, the Fallout 4 Script Extender, supports the latest Steam and GOG versions, which are not always the same build, and it cannot support the Microsoft Store release. Many players keep an earlier version for mod compatibility, so F4SE still publishes builds for older runtimes:

Address Library for F4SE Plugins provides version-independent IDs so a plugin can find game functions at runtime. Players need the file that matches their game version, so decide which runtimes you support before you release.

Why the network code lives in an F4SE plugin

Papyrus is the game's scripting language, written and compiled with the free Creation Kit on Steam. It drives quests, dialogue, terminals and settlements, but it has no network access.

So the network code goes into a native F4SE plugin in C++. The plugin calls the Neocortex API with WinHTTP or libcurl on a worker thread, then hands results to Papyrus through new native functions your scripts call. Papyrus handles the game side: Debug.Notification for simple subtitles, SetStage for quest beats, and the workshop and actor functions for settlement commands.

Voice lines in Fallout 4 are .fuz files that pair audio with lip-sync data, so a mod either generates lip data for each reply or plays the audio without mouth movement. Mantella is an existing community AI mod that also runs on F4SE.

Screenshot: Fallout 4 © Bethesda Softworks

Handling a chat reply in C++

This is how a plugin could process a /v3/chat reply with nlohmann::json: subtitles from the lines, Papyrus calls from the actions, and a quest checkpoint from flowState.

// raw = response body from POST https://api.neocortex.link/v3/chat
void HandleReply(const std::string& raw) {
    auto reply = nlohmann::json::parse(raw);
    sessionId = reply["sessionId"].get<std::string>();  // reuse on the next call
    for (auto& msg : reply["messages"]) {
        for (auto& line : msg["lines"])                  // text + emotion tag
            QueueSubtitle(msg["name"].get<std::string>(), line["text"].get<std::string>(),
                          line["emotion"].get<std::string>());
        for (auto& action : msg["actions"])              // e.g. OPEN_DOOR on door_02
            QueuePapyrusAction(action["name"].get<std::string>(),
                               action.value("targetId", std::string{}));
        std::string flow = msg.value("flowState", std::string{});
        if (!flow.empty()) QueueQuestCheckpoint(flow);   // e.g. advance a quest stage
    }
}

The Queue... functions are your own code that hands work back to the game thread.

Fallout 4 AI NPC mod release checklist

• Target runtime chosen, with the matching F4SE build and Address Library file, and a clear decision on which game versions your mod supports.
• Character designed in the Neocortex node editor: Personality, Emotion, Knowledge, Voice and the Actions your mod understands, tested in the browser for free.
• Extras added: a Conversation Flow for a companion quest, a quiz question set for the terminal, or a settlement command set.
• Plugin connected, passing replies to Papyrus on the game thread.
• API key in a config file each player fills in, never hard-coded in a shared mod.
• Tested in single-player on a separate save before touching your main playthrough.

Fair play in the Commonwealth

Fallout 4 is a single-player game, so an AI companion mod only changes the player's own world. Keep your mod free and non-commercial, follow Bethesda's terms for player-made content, and use a designed voice or one you own the rights to instead of cloning the game's cast. Players should use their own Neocortex API key so usage stays on their account.

The companion is the piece players notice first, so that is where we would begin: one Neocortex character, one plugin call, then settlement voice commands once the conversation feels right. Our foundation post on on-device voice commands for game mods covers the voice side, and the Fallout: New Vegas AI NPC mod and Skyrim AI NPC mod guides show the same ideas on other Bethesda games.

Tool versions and links checked October 2026. Modding tools change often; check each project's page for the latest release.

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