Unreal Engine 5.9 Preview, "first release built primarily with agentic workflows": a week of development, shorter QA

Epic Games on Nov. 9 (US time) released the Unreal Engine 5.9 MegaJam Preview, calling it "the first Unreal Engine release built primarily with agentic workflows." Epic's official post drew about 1,200 likes and 90,000 views.

According to a post on the Epic Developer Community forums, a handful of people directed fleets of agents to port AI tooling from the UE6 development branch and implement Web as a target platform. Agents wrote the web platform code starting from UE4's retired HTML5 platform, with engineers directing, reviewing and testing the work. Epic said it is still learning how to build the engine with multiple people directing swarms of agents in parallel, but is already seeing faster bug fixes and targeted feature work.

Epic was open about the limits. The preview had about a week of development and a shorter QA pass than usual, the team is still cleaning up some agent-written code, and parts of the web renderer are prototypes to be refactored before the full 5.9 release. "Expect rough edges, missing pieces, and things that break," Epic wrote.

Features lean toward agents too. Unreal MCP launches automatically with the editor, with expanded toolsets for rendering, source control, profiling, debugging, gameplay testing, audio, UI and level creation. Claude Code, Codex, Cursor and OpenCode work in the in-editor assistant panel, and Unreal Canvas generates concept art, images, 3D meshes and video. In replies, one user wrote "What if my system is already doing all this on 5.8?" while another argued that the person prompting, not the AI, makes the game, and asked people not to say "AI slop."