GTA 4 AI NPC Mod: AI Phone Calls, Cab Rides and Voice Commands

Yes, you can give Liberty City characters real conversations: a GTA 4 AI NPC mod is a C# script on IV-SDK .NET that sends what the player says to an AI character and plays the answer back. GTA IV was built around people, cousins who call at the worst moment, friends who want to go bowling, cab drivers with opinions, and a mod like this lets those conversations go wherever the player takes them instead of looping the same three lines. Neocortex gives your script AI characters with voices and actions, Conversation Flows, quizzes and on-device voice commands.

Screenshot: Grand Theft Auto IV: The Complete Edition © Rockstar Games

Before any code: the downgrade

IV-SDK .NET supports GTA IV 1.0.8.0 and 1.0.7.0 only. The current Steam and Rockstar Games Launcher release, the Complete Edition, has to be downgraded first, for example with the GTA IV Downgrader that the IV-SDK .NET docs point to. Many script modders pick 1.0.8.0.

If you must stay on the Complete Edition, CLEO Redux supports its 1.2.0.43 and 1.2.0.59 builds with JavaScript scripts, a lighter option for simple triggers.

Tools for a GTA 4 AI NPC mod

Once the game is on a supported version, three pieces matter:

• Ultimate ASI Loader loads native .asi plugins and is a prerequisite for IV-SDK .NET.
• IV-SDK .NET runs scripts written in C# or VB.NET on .NET Framework 4.7.2 or higher. The latest release is 1.9.1 (June 2025). Scripts are .ivsdk.dll files in the IVSDKDotNet/scripts folder, with an in-game console and manager to reload them.
• ScriptHookDotNet, the legacy .NET script hook, still powers many older mods. IV-SDK .NET can also load ScriptHookDotNet scripts (an experimental feature that keeps improving), so you do not have to choose.

Inside an IV-SDK .NET script you subscribe to Tick, read the player and world, and use anything .NET Framework offers: HttpClient for web requests, an audio library such as NAudio for voice playback, and the SDK's SettingsFile class for an .ini file. ShowSubtitleMessage puts text on screen, and the SDK's ImGui support covers anything more elaborate, like a phone transcript window.

Three Liberty City builds

Phone calls with an AI friend

GTA IV made the phone the centre of its social life. Build your own character in that spirit, an original one rather than Roman or anyone else from Rockstar's cast: say a loud, over-optimistic cousin who runs a scrapyard in Broker.

Your script rings the phone at random moments and sends the character what just happened ("player crashed into a police car", "wanted level 3", "it is 4 a.m. and raining"). The player answers by voice, speech-to-text turns it into a message, and the character replies in subtitles and audio with an emotion tag you can map to the phone animation.

Wrap it in a Conversation Flow and the call has a direction: catch up, make plans, agree to meet. When the flow reaches a checkpoint such as AGREED_TO_MEET, the API returns that keyword in flowState and your script drops a blip at the meeting spot.

Cab rides you can talk through

Hail a cab and just say where you want to go: "take me to the waypoint", "drive faster", "skip the ride". With Neocortex Voice Commands your script receives the matched commands and runs them, several per sentence if the player chains them.

The driver can be an AI character too. Feed them the district you are passing and the time of day, and they talk about Algonquin traffic, the weather and the passenger who threw up last night. Return actions like { "name": "STOP_HERE" } to end the ride early.

A trivia night in Alderney

Put a quiz host in a bar in Alderney or on a fictional late-night radio show. The quiz engine (Team plan) runs the question set you built in the dashboard, tracks the score and keeps a leaderboard, while the host reacts in character to right and wrong answers. Running it from a script takes two kinds of call:

static readonly HttpClient Http = new HttpClient();

// Start:  new { characterId = "QUIZ_HOST_ID", questionSetId = "LIBERTY_CITY_SET" }
// Answer: new { sessionId = quizSessionId, say = playerAnswer }
static async Task<string> QuizCall(string apiKey, object payload)
{
    var req = new HttpRequestMessage(HttpMethod.Post, "https://api.neocortex.link/v3/quiz");
    req.Headers.Add("x-api-key", apiKey); // loaded from the mod's .ini
    req.Content = new StringContent(JsonConvert.SerializeObject(payload), Encoding.UTF8, "application/json");
    var res = await Http.SendAsync(req);
    return await res.Content.ReadAsStringAsync(); // keep the sessionId for the next answer
}

Screenshot: Grand Theft Auto IV: The Complete Edition © Rockstar Games

Where Neocortex plugs into the script

For voice commands, you design the command set in the dashboard as actors ("cab driver"), actions ("drive", "stop", "skip") and objects ("waypoint", "here"). Push-to-talk or always listening, in multiple languages. Voice Commands is a licensed SDK: contact us for a Voice Commands license.

Build order

1. Downgrade GTA IV to 1.0.8.0, then install Ultimate ASI Loader and IV-SDK .NET.
2. Design your character, flow or quiz in the Neocortex visual editor: personality, emotions, knowledge about Liberty City, voice. Test it in the browser for free.
3. Create a C# class library that references IV-SDK .NET and builds to .ivsdk.dll.
4. Connect from the script with HttpClient off the game thread, then show subtitles and play audio on Tick.
5. Keep the API key in an .ini file each player fills in with their own key.
6. Test in single-player on a spare save.

Keeping it single-player

Rockstar's PC single-player mods policy says Take-Two generally will not act against single-player, non-commercial projects that respect third-party IP, and it excludes new stories, missions and maps. Rockstar's newer Mod Guidelines, which apply to all its games, add firmer lines: do not expand or modify Rockstar's storylines, missions or characters, and do not modify or reuse its voiceover performances. Multiplayer modding is limited to Rockstar's Creator Platform, and everything outside it must stay non-commercial. The guidelines also state that they are not a license.

For an AI mod that means Niko, Roman and the rest of the cast stay as Rockstar wrote them. Build ambient calls, cab rides and quizzes with your own characters, give them original Neocortex voices or voices you have the rights to rather than clones of Rockstar's actors, keep the mod free and out of any multiplayer, and have each player use their own Neocortex API key.

The bottom line

The hard part of a GTA 4 AI mod is the downgrade, not the dialogue. Once IV-SDK .NET is running, a single HttpClient call connects Liberty City to a Neocortex character, and the phone, the cab and the bar quiz all follow the same pattern. For other Rockstar games, see our GTA 5 AI NPC mod and GTA San Andreas and Vice City guides, and for the voice side, read about on-device voice commands for game mods.

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

Frequently Asked Questions