Epic ships a UE 5.9 preview built mostly by AI agents in a week

Epic Games released a preview of Unreal Engine 5.9 on 9 November, three days before its Epic AI MegaJam (12–15 November), and calls it “the first Unreal Engine release built primarily with agentic workflows”. According to Epic’s announcement on the Unreal Engine forums, the company decided to make the build only a week earlier. A small team directed AI agents to port AI tooling from the Unreal Engine 6 development branch and to write a Web platform target, starting from UE4’s retired HTML5 platform, while engineers reviewed and tested the output. The QA pass was shorter than usual, and Epic says it is “still cleaning up some of the agent-written code”.

The build is available in the Epic Games Launcher and as the 5.9.0-preview-1 tag on GitHub. It is not the 5.9 release, which Epic now expects “next year”. As with every preview, Epic advises testing on a copy of a project rather than converting one, and warns users to “expect rough edges, missing pieces, and things that break”.

Agent tools now start with the editor

• Unreal MCP (experimental), the Model Context Protocol server that lets AI agents call editor functions, now launches with the editor. Epic lists new toolsets for rendering, source control, profiling, debugging, gameplay testing, geometry, audio, UI and level creation, plus a Lore integration for source control and a Fab toolset that searches for and installs assets. The 5.9 release notes add a Toolset Registry that limits which toolsets agents may use, a project-level MCP settings page and an MCP Client toolset for connecting external MCP servers.
• Unreal Assistant (experimental) is an in-editor panel, connected to Unreal MCP, for working with Claude Code, Codex, Cursor or OpenCode. The release notes describe a tool-access setting with five levels: Ask, Read, Edit, Auto and Full.
• Unreal Canvas (experimental) is a shared workspace, in the editor and as a web app, where people and agents generate images, concept art, 3D meshes and video. Users connect the models they choose “using your own API keys”, so generation costs are not included with the engine.
• Python scripting gains APIs for audio, MetaSounds, modelling, physics, Niagara, materials, PCG, networking and UI.

Jam entrants should note known issue UE-412135, from the list Epic posted under the announcement: in new projects, agents get no level-editing tools, because the Toolset plugins are off by default and nothing explains why. At an Epic Games Japan session at Unreal Fest Tokyo, which GameTales covered last week, returning images in MCP format was described as expected in 5.9. The release notes list a scene-capture toolset but do not say whether MCP now returns images that way.

Browser builds return, with conditions

The new Web target runs projects in a browser through WebAssembly and WebGPU, using the mobile renderer. For now it “requires a source build and C++ project”, and Epic says Chrome gives the best experience. This is also where most of the known issues are:

• Saved games and settings are lost on reload in C++ web games built with the Launcher engine (UE-412003).
• Games crash once they use more than 2 GB of Wasm memory (UE-411671).
• Bink video is unsupported, and calling Bink Media Player functions is expected to crash (UE-411672).
• Android phones and iPhones older than the iPhone 15 Pro lack BC/DXT texture support.
• The Mac and Linux Launcher builds are missing some of the Wasm support files.
• itch.io’s limits of 500 MB per game and 200 MB per file are too small for the Lyra sample and for Development builds, and opening the packaged index.html straight from disk shows an error instead of starting the game.

Lighting, animation and removals

Lumen World Cache builds its lighting cache by path tracing the scene while the game runs, so it needs no mesh cards or card cooking. It requires hardware ray tracing and is enabled per project. Epic says improved Nanite culling helps scenes “automatically with no content changes”. A Virtual Shadow Map overview mode and a Far Shadow view help with shadow debugging, and Dynamic Wind for Nanite foliage arrives as an experimental plugin. On the animation side, the IK Retargeter gains Proximity IK, Pelvis Volume and Limb Twist; the Unreal Animation Framework gains a notify system, StateTree conditions and an AnimGen plugin; and an NVIDIA Kimodo plugin adds AI-generated animation in Sequencer.

Two removals matter if you script the editor or maintain rigs. The old Python Foundation Packages plugin has been removed. Several older Control Rig nodes are deprecated in favour of versions that reference a Control Rig asset.

Who should install it now

The preview is meant for MegaJam entrants and for teams testing agent workflows or browser delivery on project copies. Shipping projects should wait for the final 5.9 release. Epic says fixes will arrive throughout the preview period, with agents helping to triage bug reports, and that some web renderer parts are prototypes that will be refactored before 5.9 ships.

Disclosure: GameTales drafts its articles with AI assistance, including Anthropic’s Claude Code, one of the agents Unreal Assistant supports.