Epic Games says AI tools now drive Unreal Engine development
Epic's Marcus Wassmer said a 5.9 release is possible and that Claude and Codex helped eliminate long-standing cooking bugs in Unreal Engine.
Epic Games is developing Unreal Engine with AI tools, and a 5.9 version of the engine is possible, according to Marcus Wassmer, the company's Executive Vice President of Development. He said almost all current development work is happening in dev streams attached to Fortnite, Unreal Editor for Fortnite and UE6.
Wassmer described a potential 5.9 as a relatively modest update aimed at specific systems, including changes produced with AI development. He did not give a release date for the version.
The AI tools in use include Claude and Codex, which Wassmer said eliminated long-standing "non-deterministic cooking bugs" in Unreal Engine. He also said the tools help automatically monitor PC stability in Fortnite and flag problematic driver and hardware combinations.
According to Wassmer, engineers are not writing the bulk of the code; their role is to control the scope of AI use. The details were reported by gamedeveloper.com.
Epic said at Unreal Fest in Chicago in October 2025, on stage and in interviews, that it was using AI to develop code and features for Unreal Engine. The company has also said it rebuilt the Epic Games Launcher through "vibe coding" and that it runs notably faster than before.
Quick answers
Is Unreal Engine 5.9 coming?
Epic Games Executive Vice President of Development Marcus Wassmer said a version 5.9 is possible and would be a relatively modest update for specific systems. No release date was given.
Which AI tools does Epic use for Unreal Engine?
Wassmer cited Claude and Codex, which he said eliminated long-standing non-deterministic cooking bugs and help monitor PC stability in Fortnite.