Epic ships Unreal Engine 5.9 Preview, built largely by AI agents
The build adds an AI assistant inside the editor and games that run in the browser. Epic calls it unstable and says to test it on a copy of your project.
Epic Games released the Unreal Engine 5.9 MegaJam Preview on Monday, a test build of its engine that the company says was built primarily with agentic workflows. People directed teams of AI agents to do the work, and Epic's engineers reviewed and tested the results.
The agents moved AI tools over from the UE6 development branch and rebuilt the web as a target platform, starting from the HTML5 support Epic dropped in UE4. Epic puts the effort at about a week. The @UnrealEngine account framed it this way: "This isn't your typical Preview."
What's in it
The Preview opens four experimental features:
- Unreal MCP, with more tools, covering rendering, version control, profiling, debugging, geometry, audio, UI and level creation.
- Unreal Assistant, an editor panel where coding agents (Claude Code, Codex, Cursor, OpenCode) plug into Unreal MCP.
- Unreal Canvas, for making concept art, images, 3D meshes and video with AI, using the user's own API keys.
- Running projects in the browser through WebAssembly and WebGPU, which works best in Chrome.
The web target requires building from source and a C++ project. Epic acknowledges that parts of the web renderer are prototypes that will be reworked before the final release. New Python APIs also arrive for audio, MetaSounds, modeling, physics, Niagara, materials, PCG, networking and UI.
What to expect
Epic describes the build as lacking its full quality pass and tells developers to open it on a copy of their project instead of converting the original. Among the known issues, web games crash once they pass 2 GB of Wasm memory, and in new projects the MCP tool plugins ship switched off, so agents can't see levels, actors or assets.
For studios that work in Unreal, it is the first test of an engine with agentic AI in the editor and in its own construction. Epic presents the method as a way to ship more UE5 releases with faster fixes without taking focus off UE6, a reading that is Epic's own.
The Preview is available through the Epic Games Launcher and on GitHub, under the tag 5.9.0-preview-1. It launches in time for the Epic AI MegaJam 2026, which runs Nov. 12 to 15. A date for the stable 5.9 release has not been announced.
