Epic gets more specific about generative AI use in Unreal Engine and Fortnite development, saying it is more concerned about the risks of moving too slowly.

Background: Tim Sweeney stays quiet while Epic's generative AI talk turns practical

Epic Games are, by now, on a generative AI kick, but the public signal has been hard to pin down. Tim Sweeney's lips have been sealed and no reports have spewed forth, while the company has offered provocative soundbites and weird marketing lingo more than specific detail about how it is using generative AI across different parts of its business.

Development: Marcus Wassmer names Claude Code and Codex in a This Week in Videogames response

Responding to questioning from This Week in Videogames, Marcus Wassmer, Epic's executive vice president of development, gave an unusual amount of detail about the company's current deployment of the technology. He said there are a number of tools in use, but probably the most obvious ones are Claude Code and Codex with their associated AI models. He described them as helping across a broad spectrum of development.

The clearest timeline claim came from a rewrite of a significant portion of the D3D12 rendering layer. Wassmer estimated that the work would have needed three to six weeks of work for a single engineer. He said the work was actually completed in about one week, with a nice win on CPU time and fewer bugs.

Latest: bug fights, patch size, Fortnite stability, and test coverage

The particularly big recent wins Wassmer named were narrower than marketing slogans. He said the tools contributed to almost the complete elimination of non-deterministic cooking bugs that Epic had been fighting for a decade. He also said they accelerated work related to compressing shaders, which he said significantly reduce patch sizes.

He added that the tools have provided lots of help in keeping Epic's internal test suites healthy, as well as expanding those test suites for more coverage.

For Fortnite, Wassmer pointed to the additions of automatic monitoring of PC stability, automatic root cause analysis, and automatic fix generation. He claimed these have sped up the rectifying of long-running issues. Engine-wise, he said Epic have been able to attempt some larger architectural refactors with AI than they previously could, due to the amount of file changes required.

Current stage: vibe-coding from the Epic Store launcher preview to Unreal Engine

Wassmer confirmed that the Epic Store launcher preview released the other week is not the only bit of vibe-coding the company have been up to. The practice is also being used in Unreal Engine development.

"Yes, we are vibe-coding things," he said. "That means our engineers are no longer writing the bulk of the code, but they are still guiding the tools to get the architectural result we want. 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."

He also offered the company's justification for moving quickly: "We are more concerned about the risks of moving too slowly than we are about AI skepticism."

What the disclosure means for readers

The change from earlier marketing talk is that Epic is now putting named tools and measurable development claims behind the generative AI push. For readers, the practical items to watch are not secret gameplay promises but internal development signals: smaller patch sizes, faster repair of long-running Fortnite issues, broader test coverage, and a one-week versus three-to-six-week comparison for a D3D12 rendering-layer task.

Epic's stance also has a disclosure angle. Wassmer and Epic are not hiding the fact they are embracing the technology, even as Tim Sweeney hates the concept of developers having to disclose their generative AI use to prospective customers or users.

At this stage, Epic's public position is that generative AI is already embedded in named engineering workflows, and that the company is more worried about falling behind than about convincing skeptics.