Epic says its engineers no longer write most Unreal Engine 6 and Fortnite code

Epic Games’ executive vice president of development, Marcus Wassmer, has confirmed that AI tools now write most of the code for Fortnite and Unreal Engine 6, with human engineers guiding the output. He made the remarks in an interview with This Week in Video Games, and several outlets reported them on Wednesday, October 28.

“Yes, we are vibe-coding things,” Wassmer said. “That means our engineers are no longer writing the bulk of the code,” he added, though they still steer the tools toward the architecture Epic wants.¹ Vibe coding means describing what you want to an AI model and letting it produce the code, then reviewing and adjusting the result.

Wassmer named Claude Code and Codex, along with their associated AI models, as the most obvious tools in use.² He also said “almost all development happening right now” takes place in the development streams tied to Fortnite, Unreal Editor for Fortnite and UE6.¹

He described specific results, all of them his own account:

• Almost complete elimination of non-deterministic cooking bugs that Epic has fought for a decade. Cooking is the step that turns game content into a shippable build, and non-deterministic means the same input could produce different results.
• Faster work on shader compression, which together with the cooking fixes reduces patch sizes.
• A rewrite of a large part of the D3D12 rendering layer. Wassmer said he had estimated three to six weeks of work for one engineer. It was finished in about a week, with a gain in CPU time and fewer bugs.
• Help keeping Epic’s internal test suites healthy and expanding their coverage.²

For Fortnite, he cited automatic monitoring of PC stability, plus automatic root cause analysis and automatic fix generation. He said these have sped up fixes for long-running problems, and that Epic has been able to attempt larger architectural refactors than before because AI can handle the volume of file changes.²

Wassmer stressed that the engine is not being built in one pass. “We’re not ‘one-shotting’ the engine,” he said, describing an iterative process meant to ship features developers want while keeping the engine within its memory, performance and scalability limits.¹ He also claimed the tools will help Epic ship updates faster and with fewer bugs.¹ The Verge reported that he spoke of faster feature development and room for engineers to explore ideas they had not had time to tackle.³

Epic is not hedging on the approach. “We are more concerned about the risks of moving too slowly than we are about AI skepticism,” Wassmer said, adding that a halfway approach is not viable and that Epic plans to share best practices with other developers.¹

The interview follows other recent moves. Epic said earlier this month that it vibe-coded the new Epic Games Launcher, and CEO Tim Sweeney has said the company is retooling for “maximum AI acceleration.”³

The whole story rests on Wassmer’s own statements, repeated across outlets. The benefits, speed gains and bug counts are his claims, and no outside measurement of them appears in the coverage.

Our read: Epic has moved from broad talk about AI to named tools and concrete jobs, and that is more useful to developers than slogans. Unreal Engine is infrastructure for a great many studios, so the real test is whether the promised faster updates and fewer bugs show up in UE6 releases. Wassmer’s own wording points to human review as the safeguard. Developers should watch release notes and bug trackers, not interviews, for evidence of how well that holds.

Footnotes

1. eurogamer.net, “Epic confirms AI tools write bulk of Unreal Engine 6 and Fortnite code”. Retrieved October 28, 2026. ↩ ↩² ↩³ ↩⁴ ↩⁵

2. Rock Paper Shotgun, ““We are more concerned about the risks of moving too slowly”: Epic get more specific about genAI use in Unreal Engine and Fortnite development”. Retrieved October 28, 2026. ↩ ↩² ↩³

3. The Verge, “Epic is using AI to help build Unreal Engine.”. Retrieved October 28, 2026. ↩ ↩²