Epic Games VP Confirms Use of Claude Code and Other AI Tools for Unreal Engine Development, Citing D3D12 Rewrite

Epic Games Executive Vice President of Development Marcus Wassmer has confirmed to This Week in Videogames (TWIV) that the company is using AI tools to "develop code and features" for Unreal Engine. This statement follows CEO Tim Sweeney's earlier announcement of a "huge pivot" towards AI tools, marking a transition of AI application in core engine infrastructure from experimental phases to active production.

Wassmer noted that almost all current development work is happening in dev streams attached to Fortnite, Unreal Editor for Fortnite (UEFN), and Unreal Engine 6 (UE6). He specifically identified the tools being used: "Probably the most obvious ones are Claude Code and Codex with their associated AI models." These tools are assisting across a broad spectrum of development, including the near-complete elimination of non-deterministic cooking bugs that had plagued the team for a decade, and accelerated shader compression work that significantly reduces patch sizes.

Regarding specific technical breakthroughs, Wassmer cited an AI-assisted rewrite of a significant portion of the D3D12 rendering layer. He estimated this task would have required three to six weeks for a single engineer but was completed in about one week, resulting in improved CPU time and fewer bugs. Additionally, AI is being used for automatic PC stability monitoring, detecting issues with specific driver/hardware combinations, and generating automatic fixes to address the long tail of persistent PC issues in Fortnite and Unreal Engine.

Addressing concerns about "vibe coding," Wassmer acknowledged that the team is indeed vibe-coding, but clarified that engineers are still guiding the tools to achieve desired architectural results rather than letting AI generate the entire engine in one shot. "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 said. He emphasized that Epic is more concerned about the risk of moving too slowly than about AI skepticism, arguing that software developed correctly with AI will be better and more responsive to customer feedback.