Epic is vibe-coding Unreal Engine 6 with Claude Code and Codex
Epic Games is using AI tools to develop code for Unreal Engine 6, Fortnite, and the Epic Games Launcher. That confirmation came from both CEO Tim Sweeney on X and from Marcus Wassmer, Epic’s executive VP of development, in a statement to This Week in Videogames.
What Epic Is Actually Doing
Wassmer describes it as vibe-coding: engineers are no longer writing the bulk of the code, but they are still guiding the tools toward the architectural results they want. His words: “We’re not ‘one-shotting’ the engine; we’re iterating with AI to ship features developers want and keep the engine within the memory, performance, and scalability envelopes.”
The specific tools named are Claude Code and Codex. Almost all development happening right now is running through dev streams attached to Fortnite, Unreal Editor for Fortnite, and UE6.
Concrete Wins They’re Claiming
- Near-complete elimination of non-deterministic cooking bugs that Epic had been fighting for a decade
- Accelerated work on shader compression, which reduces patch sizes
- A rewrite of a significant portion of the D3D12 rendering layer: Wassmer estimated the work at three to six weeks for a single engineer, but it was completed in about one week with a CPU time improvement and fewer bugs
The Broader Context
This disclosure sits inside a busy few weeks for Epic on the AI front. The company also announced an AI game jam (then walked back the AI requirement), Sweeney publicly criticized Steam’s AI disclosure requirements, and Epic claimed it vibe-coded the Epic Games Launcher to outperform a competitor.
Wassmer’s position on skepticism is direct: “We are more concerned about the risks of moving too slowly than we are about AI skepticism.” He adds that the company does not think a halfway approach to AI in development is viable and plans to share best practices openly with other developers.
For anyone building on Unreal Engine or shipping games through Epic’s ecosystem, this is a signal worth tracking. The tools doing the work are commercially available today.
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