Epic details AI’s role in engine and Fortnite development

Epic executive Marcus Wassmer says engineers now guide AI tools that write most of the code for Unreal Engine development. The shift reaches Fortnite too. "Yes, we are vibe-coding things," he said, adding that Epic's engineers "are no longer writing the bulk of the code, but they are still guiding the tools to get the architectural result we want."

Wassmer is careful about what that does not mean. Epic is not asking the tools to spit out an engine in one go. Instead, the team iterates with AI to ship features developers want while keeping Unreal Engine within memory, performance, and scalability constraints.

He also named the tools: Claude Code and Codex, along with their associated models, which he says assist on a wide range of development work. The examples are unusually concrete for a subject that usually runs on slogans. AI helped nearly eliminate non-deterministic cooking bugs. It accelerated shader compression work that reduced patch sizes.

Wassmer's biggest single claim is that AI helped rewrite the D3D12 rendering layer in about one week. He adds that AI helps maintain Epic's internal test suites and expand their coverage.

Speed over skepticism

"We are more concerned about the risks of moving too slowly than we are about AI skepticism," Wassmer said. The company has also said it vibe-coded a new Epic Games Launcher, so this approach clearly is not limited to the engine.

Wassmer says that, for Fortnite players, the most tangible piece is on PC. He says the game has automatic PC stability monitoring, root-cause analysis, and fix generation to help resolve long-running issues.