# Halo 3: Mythic — OpenH3M

Canonical: https://playable.wtf/games/halo-3-openh3m/

Project ID: project:halo-3-openh3m

Halo 3 Mythic Custom Games, Forge and local split-screen for native Windows.

## About this version

GTTeancum’s OpenH3M recompiles the Halo 3: ODST multiplayer disc for Windows x64 using ReXGlue. Beta 0.8 documents Custom Games, Forge and up to four local players, with no Xbox LIVE or matchmaking.

Source / build. Shooter.

[Build instructions](https://github.com/GTTeancum/OpenH3M)

## Halo’s multiplayer disc, on its own terms

OpenH3M targets the Halo 3 Mythic multiplayer disc bundled with ODST, rather than its campaign. Beta 0.8 documents Custom Games, Forge and one to four local players at the original 30 FPS target. It has no Xbox LIVE or matchmaking; System Link remains untested.

Custom Games provides the route into a local match, while Forge lets you switch between player and build modes. The creator illustrates split-screen play on Last Resort and Construct. That makes this Windows recompilation a project for local Halo sessions, with compatible controllers ready before entering the lobby.

Sources: [OpenH3M · beta 0.8 README](https://github.com/GTTeancum/OpenH3M)

## Preparing a local match or Forge session

Use your own extracted Mythic disc files, preserving default.xex and maps inside a game folder beside OpenH3M.exe. The README links a Windows release package and describes a 1280×720 windowed first launch. Windows 10 or 11, a Direct3D 12 GPU and compatible controllers are the documented starting point.

Additional local players join with Start. In Forge, D-pad Up switches between player and build modes. Theater is accessible, but recording and saved-film playback remain less established than the documented Custom Games and Forge routes.

Sources: [OpenH3M · beta 0.8 README](https://github.com/GTTeancum/OpenH3M)

## For players building from source

The source path uses the win-amd64-release CMake preset and launches halo3mp.exe with an extracted-disc directory as game\_data\_root and the xenos GPU plugin. That differs from the packaged application’s automatic adjacent game folder. Keep the complete extracted directory available rather than pointing the developer executable at an ISO. The original disc data and rebuilt program remain separate parts of the installation, even when you compile the runtime yourself.

Sources: [OpenH3M · build instructions](https://raw.githubusercontent.com/GTTeancum/OpenH3M/HEAD/halo3mp/BUILD.md)

## Do I need the original game files?

Supply legally obtained files from Halo 3: ODST Multiplayer Disc (Disc 2), preserving default.xex and maps/ under the game folder. This is the Mythic multiplayer disc, not the ODST campaign disc.

Creator-reported: [Project guide](https://raw.githubusercontent.com/GTTeancum/OpenH3M/HEAD/README.md)

## How do I get started?

Consult the original repository for the current supported files, build process and limitations.

Creator-reported: [Project guide](https://github.com/GTTeancum/OpenH3M)

## Which devices and browsers work?

The creator requires 64-bit Windows 10 or 11 and a Direct3D 12 GPU.

Creator-reported: [Project guide](https://raw.githubusercontent.com/GTTeancum/OpenH3M/HEAD/README.md)

## What are the controls?

Xbox/XInput controllers use the original controls. Additional local players join with Start; D-pad Up switches Forge modes.

Creator-reported: [Project guide](https://raw.githubusercontent.com/GTTeancum/OpenH3M/HEAD/README.md)

## Can I play multiplayer?

Beta 0.8 documents one to four local split-screen players. Matchmaking and Xbox LIVE are unsupported; System Link remains untested by the creator.

Creator-reported: [Project guide](https://raw.githubusercontent.com/GTTeancum/OpenH3M/HEAD/README.md)

## What is included in this version?

Custom Games and Forge are documented. Theater is reachable, but recording and saved-film playback are not fully validated by the creator.

Creator-reported: [Project guide](https://raw.githubusercontent.com/GTTeancum/OpenH3M/HEAD/README.md)

## Documented support

- Controller: Supported · Creator-reported
- Multiplayer: Supported · Creator-reported
- Local multiplayer: Supported · Creator-reported

## Credits and project

- [Original project](https://github.com/GTTeancum/OpenH3M)