Epic Games confirms Claude Code and Codex now write much of the code behind Unreal Engine and Fortnite

Epic Games has confirmed that AI coding agents are now a routine part of how it builds Unreal Engine and Fortnite. Chief executive Tim Sweeney wrote on X, "Yes, we are now using AI tools to develop code for Unreal Engine", and Marcus Wassmer, the executive in charge of engine development, gave more detail in statements reported on October 28 by PC Gamer, GamingBolt and This Week in Videogames.

What Epic says the tools are doing

Wassmer named two products: Anthropic's Claude Code and OpenAI's Codex. According to PC Gamer, he said Epic's engineers no longer write most of the code themselves; instead they direct the tools toward the architecture they want. He also said almost all current development happens in branches tied to Fortnite, Unreal Editor for Fortnite and the upcoming Unreal Engine 6.

Epic points to several concrete results. The company says the tools have nearly eliminated non-deterministic "cooking" bugs, which occur when game assets are prepared for a target platform and which its teams had chased for roughly a decade. AI assistance also sped up shader compression work, which Epic says shrinks patch sizes. Wassmer said a rewrite of a large part of the D3D12 rendering layer took about a week, against his estimate of three to six weeks for a single engineer, and that it lowered CPU time and bug counts. On Fortnite, Epic describes automated PC stability monitoring that spots driver and hardware problems, then analyses root causes and proposes fixes.

A sharp turn from 2025

The statements mark a change of position. GamingBolt notes that in 2025 Sweeney said Epic was not using AI tools in development. In June, Wassmer's Unreal Engine 6 roadmap said the company was still evaluating what worked for code generation. On October 12, Sweeney posted that a "huge pivot" was underway to retool developers for AI, adding that the aim was to build more, not to do the same work with fewer people. Epic also said in mid-October that it had "vibe coded" a new Preview version of its games launcher.

Open questions

All of the performance figures come from Epic itself and have not been independently checked. The shift also lands in a sensitive context: The Next Web recalls that Epic cut more than 1,000 jobs in March 2026, which Sweeney said was unrelated to AI, and Bloomberg reported that a Disney-partnered team was told to go "AI first". Wassmer told This Week in Videogames that Epic worries more about moving too slowly than about AI skepticism.