Epic Games says it built the Unreal Engine 5.9 Preview primarily with AI agents. Developers who use the engine are now divided over whether that is a sound way to ship it.
Epic released the Preview on November 9, 2026. The company calls it the first Unreal Engine release built primarily with agentic workflows. A handful of engineers directed fleets of agents to port AI tooling from the UE6 development branch. The agents also wrote the code for a web platform, starting from UE4’s retired HTML5 platform. Engineers reviewed and tested that work.
The Preview took about a week to build. Epic says it is still cleaning up some agent-written code. Parts of the web renderer are prototypes that will be refactored before the full release.
What the Preview adds
Most new features are marked Experimental. Unreal MCP, the editor’s connection point for the Model Context Protocol (a standard that lets AI tools talk to software), now gives agents more toolsets. The release notes name Blueprints, editor actions, MVVM, Slate inspection, performance, files, scene capture, console, Texture Graph and widget animation. A Toolset Registry controls which of these agents may use.
Unreal Assistant is an in-editor panel and the clearest example of unreal engine ai in this release. Its notification settings can play a sound, flash the taskbar or show a badge when it needs attention. A tool-access setting with five levels (Ask, Read, Edit, Auto and Full) controls how much it can do without asking. Epic names Claude Code as a supported coding agent. The release notes also list Google Gemini among the generative-service integrations.
Unreal Canvas is a shared workspace where people and agents build and revise content. Its canvases hold text, images, video and mesh generators, each driven by a prompt and a generation service the user chooses. Two companion plugins ship with it. Unreal Canvas Bridge exposes Movie Render Graph rendering to Canvas as MCP tools, and it needs the MCP plugin. Unreal Canvas Spatial Annotations places notes in the 3D scene and captures that scene for Canvas.
Canvas’s prompt-driven generators raise questions about AI-made imagery, and Martin Bonnevier’s Mesmerizing AI Art Visions shows where that style can lead.
Python scripting also improves. Developers can manage extra Python search paths. New libraries let scripts edit Blueprints, chooser tables, StateTrees and Dataflow graphs. The old Python Foundation Packages plugin has been removed.
Rendering and animation changes
Lumen World Cache changes how Lumen, the engine’s real-time global illumination system, stores light. Lumen used to rely on mesh cards, small captures prepared for each mesh. The new cache is built while the game runs, by path tracing the scene. Epic says it needs no mesh fix-up or card cooking. It requires Hardware Ray Tracing and must be switched on for each project.
Adaptive Voxel-Based Order Independent Transparency, or AVBOIT, sorts overlapping translucent surfaces such as glass, smoke and particles. The result is correct whatever order they are drawn in. It works with both Nanite and non-Nanite translucency. Translucent materials must output only their own colour for it to composite correctly.
Nanite culling decides each frame which Nanite geometry is visible, and it now handles skinned, spline-deformed and World Position Offset meshes separately. Scenes gain the speed automatically, and the benefit grows with scene size. Dynamic Wind, an Experimental plugin, simulates each bone’s motion on the GPU. It combines a slow sway with a fast flutter, and it reacts to radial bursts, swirls and directional pushes.
On the animation side, the IK Retargeter adds Proximity IK, Pelvis Volume and Limb Twist. The new UAF AnimGen plugin brings AI-driven animation generation into the Unreal Animation Framework. A separate NVIDIA Kimodo plugin lets animators make characters follow trajectories and describe animations in text.
Character rigs and animation tools like these also shape how game worlds feel, so Why Game Designers Return to Familiar Visual Worlds is a useful follow-up on recurring settings.
Browser builds in the unreal engine 5.9 preview
Version 5.9 brings back the web as a target platform. Projects compile to WebAssembly, a binary format browsers can run, and render with WebGPU, a modern browser graphics interface. Developers can run projects in a browser again, but the feature is Experimental.
Epic says the aim of the unreal engine 5.9 preview is to learn how to direct many agents working in parallel. The company says the approach lets it ship more UE5 updates and faster bug fixes “without pulling focus from UE6.” The Preview is also tied to the 2026 Epic AI MegaJam, which runs November 12 to 15.
A divided reaction
Developers on X have reacted sharply. One wrote that they will stay on 5.8, arguing that large language models help but that the AI features in this Preview cross a line. That developer asked why 3D model generation was added at all. Another said they dislike the asset generation features but welcome deeper agent integration. That developer said they appreciated that agents are not forced into the editor.
Both reactions point to the same question. Epic is asking developers to trust agent-written code in a tool that millions of projects depend on. The unreal engine 5.9 preview is unstable by Epic’s own description. Epic’s developer documentation on its website lists the full release notes. Anyone considering the Preview should test it on a copy of a project.
Via creativebloq.com
Frequently asked questions
Who built the Unreal Engine 5.9 Preview, and how long did it take?
Epic Games says the Unreal Engine 5.9 Preview was built primarily with AI agents, directed by a handful of engineers who reviewed and tested the work. The Preview took about a week to build, and Epic says it is still cleaning up some agent-written code.
What is Lumen World Cache in Unreal Engine 5.9?
Lumen World Cache changes how Lumen, the engine’s real-time global illumination system, stores light. Instead of relying on mesh cards, the cache is built while the game runs by path tracing the scene, and it requires Hardware Ray Tracing and must be enabled for each project.
What are the tool-access levels for Unreal Assistant?
Unreal Assistant has a tool-access setting with five levels: Ask, Read, Edit, Auto and Full. These levels control how much the assistant can do without asking the user first.
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