Epic says engineers no longer write most of the Unreal code. The week-long rewrite is their estimate

Epic Games has said, in the words of its development chief, that the people are no longer writing most of the code. Marcus Wassmer told This Week in Videogames, in remarks reported on 28 October, “Yes, we are vibe-coding things.” He defined it: engineers are no longer writing the bulk of the code, but they still guide the tools toward the architecture Epic wants. He named Claude Code and Codex. He said almost all current work sits on the development streams attached to Fortnite, Unreal Editor for Fortnite, and Unreal Engine 6. Tim Sweeney, the chief executive, had already confirmed on X that the company is using AI tools to develop Unreal Engine code. A confirmation that the tools are in use is not a measurement of how much of the engine they wrote.

The results Wassmer offered are specific, and they are still his. He said the tools nearly eliminated non-deterministic cooking bugs the team had fought for a decade, and sped up shader compression enough to shrink patches. He said a rewrite of a significant part of the Direct3D 12 rendering layer, which he had estimated at three to six weeks for one engineer, was done in about a week, with a gain in processor time and fewer bugs. “I estimated” is the right tense. The week, the decade, and the performance win are Epic’s account of Epic’s diff. No outside lab has rerun the bugs, and Epic has not published the change in patch size.

He also drew a line the slogan leaves out. The company is not, he said, “one-shotting” the engine. People iterate, and the result still has to fit memory, performance and scale. That is a narrower claim than “AI built Unreal.” It is a claim that a coding agent is now the default first draft, on the streams that will become Unreal Engine 6. Epic’s own roadmap, posted in June, still has early access for that engine at the end of 2027. A tool that shortens a week of rendering work does not move that date by itself.

For a robotics desk the useful comparison is who is allowed to sign the code. Epic’s engineers are still the ones who accept the architecture. A game engine that ships to millions of machines is a harsh test of generated code, because a bad frame shows up. It is not the same test as a robot, where a bad line can move a joint. Until Epic publishes how much of a named release was model-written, and how much was reverted, the shift is a management statement. It is a clear one. It is not an audit.