F4MP

Fallout 4 Multiplayer Mod.

This project is experimental and not "playable" in the normal sense. Expect game-breaking bugs and crashes. Back up your game and saves before using it. No other mods are supported at the same time.

This is a fork of cokwa/F4MP with additional work on shared combat (see below).

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What's new in this fork

The base mod uses a "clone the player" model: it shares each player's appearance, position, and animation as a puppet actor, but every player is otherwise in their own single-player world (separate quests, loot, enemies, saves).

This fork adds Level 1 shared combat — you now fight the same enemies together:

• Shared NPC health & death. The client that owns a given enemy (the first to see it) streams that enemy's health fraction; everyone else mirrors it and kills their local copy when it dies. So when one player drops a raider, it drops for both of you.
• Cross-client damage routing. If a player who does not own an enemy shoots it, the hit is routed to the owning client, applied to the authoritative actor, and the resulting health/death streams back. (The owner's own hits are applied locally, so damage is never double-counted.)

Implementation notes live in docs/SHARED_PROGRESSION.md (what shared progression is/isn't possible) and docs/TODO.md (remaining work: connection-stability fixes, settlement sync, the "shared combat" roadmap, and known polish items).

Status: the C++ plugin and the Papyrus scripts both compile cleanly, and the full build/deploy pipeline is verified. The new combat features have not yet been runtime-tested in-game (that needs two connected clients on Fallout 4 1.10.163).

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Requirements

For…	You need
Running the mod	Fallout 4 1.10.163 (the "classic"/pre-Next-Gen build) + F4SE 0.6.23
Building the plugin/server	Visual Studio 2022/2026 with the Desktop development with C++ workload (MSVC v143)
Recompiling the Papyrus scripts	the Fallout 4 Creation Kit (free on Steam — it provides the Papyrus compiler)

⚠️ Game version matters. The current Steam build of Fallout 4 is the Next-Gen update, which F4SE 0.6.23 and this plugin will not load. You must run the game on 1.10.163. Downgrading is a manual Steam step the helper script cannot automate.

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How to install & play

There are two paths, depending on whether you just want to play or want to build from source. Pick one.

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A) Players — easiest (no Visual Studio, no Creation Kit, no source code)

Use the prebuilt release — you run a single installer.

1. Download the latest F4MP-Steam-*.zip from the Releases page.
2. Extract the whole zip. Your browser saves it to your Downloads folder; right-click the zip → Extract All. Keep Install-F4MP.bat, Install-F4MP.ps1, README.txt, and the Data folder together in the extracted folder.
3. Right-click Install-F4MP.bat → "Run as administrator." It auto-detects Fallout 4, checks the version, downloads F4SE 0.6.23 if it's missing, copies the mod files in, and enables the plugin. (If your game isn't found, run Install-F4MP.ps1 -Fallout4Path "X:\...\Fallout 4" from a terminal.)
4. Make sure Fallout 4 is on 1.10.163 — see Requirements. Downgrade first if you're on the Next-Gen update.
5. Launch the game with f4se_loader.exe (in your Fallout 4 folder — not the normal Steam Play button). Load a save.
6. Connect:
   • Steam co-op (both players Steam friends, both on this build): one presses F5 to host a lobby, the other presses F6 to join.
   • Classic direct-IP: press F1 (requires a running server — see Server).

🟢 Players do not need Visual Studio, the Creation Kit, or this source repo — just the release zip.

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B) Developers — build from source

This path does require Visual Studio 2022/2026 (or the standalone Build Tools for Visual Studio) with the Desktop development with C++ workload, plus the Creation Kit to recompile the Papyrus scripts. See Requirements.

The helper scripts in scripts/ build and install everything for you:

• Full setup — double-click scripts\setup-everything.bat (needs internet). It auto-detects your already-installed Visual Studio's MSBuild (it does not install Visual Studio — you must have it first) and your Fallout 4 install, builds f4mp.dll, downloads & installs F4SE 0.6.23 + the mod, enables it, and compiles the Papyrus scripts (if the CK is present).
• Rebuild + redeploy your local changes — double-click scripts\deploy.bat (no downloads).

Script options

Run from a terminal (or append after the .bat):

powershell -ExecutionPolicy Bypass -File scripts\deploy.ps1 [options]

Option	Effect
-All	-GetF4SE -GetMod -SetEnvVar (what setup-everything.bat runs).
-GetF4SE	Download + install F4SE 0.6.23 into the game folder.
-GetMod	Download + install f4mp.esp + baseline scripts and enable the plugin.
-SetEnvVar	Persist FALLOUT4_PATH so plain Visual Studio builds auto-copy the DLL.
-BuildServer	Also build f4mp_server.exe.
-SkipBuild	Don't rebuild; just (re)deploy.
-Configuration Release	Build Release instead of Debug.
-Fallout4Path "X:\...\Fallout 4"	Use this if the game isn't auto-detected.
-CreationKitPath "X:\...\Fallout 4 1946160"	Use this if the CK isn't auto-detected.
-Uninstall	Remove the F4MP files this script installed (DLL, esp, scripts, plugin entry).
-RemoveF4SE	With -Uninstall, also remove the F4SE loader files.

The script auto-detects the Creation Kit whether it's installed inside the game folder or as a separate Steam app folder (e.g. …\steamapps\common\Fallout 4 1946160), extracts the base script sources from Base.zip, and compiles using F4SE's extended sources so the new features are active. If the CK isn't present, the baseline .pex from the mod download are used and the new features stay dormant until you install the CK and re-run.

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Where files are deployed

All under your …\steamapps\common\Fallout 4\ folder:

File	Location	Installed by
f4mp.dll	Data\F4SE\Plugins\	script (deploy)
F4MP*.psc (sources)	Data\Scripts\Source\User\	script
F4MP*.pex (compiled)	Data\Scripts\	script (needs CK)
f4mp.esp + quest fragment	Data\ / Data\Scripts\Fragments\Quests\	script (-GetMod)
F4SE 0.6.23 (f4se_loader.exe, f4se_1_10_163.dll, …)	game root + Data\	script (-GetF4SE)

Where does f4mp.esp come from?

The mod plugin is not in this source repo. It ships in the upstream release cokwa/F4MP-Archive, v0.1-indev (release-0.1indev.zip → nested f4mp-client.zip → f4mp.esp). The -GetMod option downloads and installs it for you.

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Manual build (if you prefer)

Repo root = the folder containing f4se.sln.

Plugin (f4mp.dll):

msbuild f4mp\f4mp.vcxproj /p:Configuration=Debug /p:Platform=x64 /p:SolutionDir=<repo-root>\

Server (f4mp_server.exe, no game/F4SE dependency):

msbuild f4mp_server\f4mp_server.vcxproj /p:Configuration=Debug /p:Platform=x64 /p:SolutionDir=<repo-root>\

Build output lands in x64\Debug\. Setting the FALLOUT4_PATH environment variable makes the plugin's post-build step auto-copy f4mp.dll into Data\F4SE\Plugins\.

Plugin build prerequisite (not in this repo): the plugin references the F4SE SDK as sibling folders (..\f4se\, ..\f4se_common\, ..\..\common\). Clone ianpatt/f4se (v0.6.23) and ianpatt/common, place f4se/, f4se_common/, xbyak/, and common/ per those paths, retarget them to v143, and set WindowsTargetPlatformVersion to 10.0. The server has no such dependency.

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Server

# build once (or use deploy.ps1 -BuildServer)
msbuild f4mp_server\f4mp_server.vcxproj /p:Configuration=Debug /p:Platform=x64 /p:SolutionDir=<repo-root>\

Create server_config.txt next to f4mp_server.exe: line 1 = bind address (usually localhost), line 2 = port (default 7779), line 3 (optional) = player spawn point x y z (defaults to 886 -426 -1550). Then run:

f4mp_server.exe

Anyone on your local network can connect. To play over the internet, forward port 7779 (both TCP & UDP); joiners put your public IP in their config.txt (Documents\My Games\Fallout4\F4MP\config.txt).

config.txt is read by the client at load: line 1 = host address (IP/hostname; blank = localhost), line 2 = port (optional, defaults to 7779). Pressing F1 in-game connects to whatever it specifies, so a non-default host port no longer needs a recompile — just edit the file. Example:

203.0.113.7
7779

Running the game

Launch Fallout 4 via f4se_loader.exe (not the normal launcher) and load a save. Then connect one of two ways:

Steam co-op (no server, no IP — recommended): both players must be Steam friends on the same build.

• One player presses F5 to host a Steam lobby.
• The other presses F6 to join it.
• The console window prints RECV "hello…" / RECV "ack…" once the peer link is up.

Classic direct-IP:

1. Start f4mp_server.exe.
2. Launch via f4se_loader.exe, load a save.
3. Press F1 to connect.

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License & credits

F4MP — Copyright (C) 2020 Hyunsung Go. See LICENSE. Upstream: https://github.com/cokwa/F4MP/.