Epic Games Confirms It Is Vibe-Coding Unreal Engine 6 and Fortnite With AI Tools

Epic Games has confirmed that artificial intelligence is now writing a meaningful share of the code behind Unreal Engine 6 and Fortnite. Epic founder and CEO Tim Sweeney stated the shift directly on X, and the company’s executive VP of development, Marcus Wassmer, followed up with specifics on how deep that AI involvement actually goes.

Engineers Are Guiding the Tools, Not Writing the Bulk of the Code

Wassmer explained that Epic’s engineers no longer write most of their code by hand. Instead, they steer AI tools, including Claude Code and Codex, toward the architecture the team wants, rather than letting the tools generate entire systems in one pass. He said the studio is not trying to produce the whole engine in a single AI-driven attempt, but is iterating with the tools to ship the features developers want while keeping the engine within its usual memory, performance, and scalability limits.

Unreal Engine 5.8 shipped an experimental MCP server integration earlier this year, the groundwork for the AI-assisted workflows Epic is now using across Unreal Engine 6 and Fortnite development.

A Rendering Layer Rewrite That Took One Week Instead of Six

As one example, Wassmer pointed to a rewrite of a significant portion of Unreal Engine’s D3D12 rendering layer, work he estimated would normally take a single engineer three to six weeks. With AI assistance, it reportedly took about a week, with a better result on CPU time and fewer bugs than expected. He also credited the tools with nearly eliminating nondeterministic cooking bugs the team had fought for a decade, and with speeding up shader compression work that helps shrink patch sizes. Almost all of Epic’s current development, across Fortnite, Unreal Editor for Fortnite, and Unreal Engine 6 itself, now runs through these AI-assisted workflows.

The Rebuilt Launcher Was the First Public Sign

Epic had already previewed what this approach looks like in practice earlier this month, releasing a new Epic Games Launcher that it says was largely vibe-coded, with the company framing traditional hand-written development as too slow for what it wanted to ship. That rebuild followed a broader pivot Epic signaled back in October, when Sweeney first described a company-wide retooling for AI acceleration across its engineering teams.

“Yes, we are now using AI tools to develop code for Unreal Engine.”

Tim Sweeney, Founder and CEO, Epic Games

Sweeney Is Also Fighting Mandatory AI Disclosures on Steam

The confirmation lands alongside a separate dispute over how AI use should be disclosed to players. Sweeney has criticized Valve’s requirement that Steam store listings carry AI disclosure statements, comparing it to forcing developers to write a political essay that can later be used against them. Wassmer, for his part, argues Epic’s approach is the opposite of secrecy: the company would rather be upfront about its AI use and let its games and tools speak for themselves than let skepticism go unaddressed.

Whether that openness changes how players feel about AI-assisted development remains to be seen, but it leaves little doubt about how central these tools have already become to how Unreal Engine 6 and Fortnite get built from here.

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Picture Source: Epic Games / Unreal Engine