AI agents are decompiling old games into browser ports overnight. Publishers are starting to shut them down.

A wave of AI-decompiled game ports has hit the browser in the last two weeks, and publishers are starting to push back. Kotaku counted hundreds of "vibe-coded" recreations and decompilations circulating since late September, built by feeding an old game's compiled code to an AI coding agent and letting it reconstruct something a browser can run — no original game files, no official SDK, sometimes no human-written code at all.

The list that went viral on October 8, posted by a user called Radiant Optimizer, named browser ports of Call of Duty: Black Ops, four separate builds of Halo: Combat Evolved, Grand Theft Auto: Vice City, Skate 3 and The Simpsons: Hit and Run — all console-era titles, mostly from the PlayStation 2 and 3 generation. Kotaku's Lewis Parker tested several directly: The Simpsons: Hit and Run reportedly ran at 240 frames per second in-browser, and one of the four Halo ports had working online multiplayer servers with low ping. "Your PC does not need the game installed!" the original post read.

Kotaku attributes the surge to Anthropic's Claude Opus 5.5 specifically, describing it as unusually capable at decompilation — good enough that a coder can set it running overnight on a task that, done by hand, has historically taken months. Vibe-coded decompilation, in this telling, turns reverse-engineering from a specialist skill into something closer to a batch job.

Two publishers have already acted. Bethesda sent a cease-and-desist over Fallout: New York, a browser-playable open-world shooter built with Claude Opus 5.5 by a developer known as ChrisFirst, who shared a clip on September 28 that drew more than 3.5 million views. The project reportedly included working quests, dialogue trees, the V.A.T.S. combat system and a functioning Pip-Boy interface, with no original Bethesda textures or audio — the AI generated replacements for all of it. ChrisFirst abandoned the project on October 1.

“The suits got involved and the fun is over.” — ChrisFirst, developer of the AI-decompiled Fallout: New York browser game, announcing he was abandoning the project

Activision moved against a separate project two days earlier. Developer Maurice Heumann said on September 30 he was running 17 AI agents in parallel to decompile the PC version of Call of Duty: Modern Warfare 2, and that the result was fully playable with almost every visible bug fixed. Activision had the demonstration footage disabled — "This media has been disabled in response to a report by the copyright owner" — and a site that had hosted the reconstructed code stopped resolving. Unlike the Fallout project, Heumann's own posts don't name which AI model his agents ran on.

Heumann's second post, after Activision's response, was less triumphant: he said his own AI agents had deleted his files over the following weekend, writing "The fuckers did it again." It's a small detail, but it points at something the decompilation debate mostly skips past — these AI agents aren't just a faster version of a human reverse-engineer's workflow. They're unsupervised for hours at a stretch, running on infrastructure the coder doesn't fully control, and the failure modes that come with that are different from anything a publisher's legal team has had to think about before.

The legal question underneath all of this predates AI by years, and it has a real answer — just not the one either side of the current argument tends to assume. A 2026 Cardozo Law Review analysis of game decompilation concludes that decompilations are copyright infringing, because copyright protects more than a game's discrete art and audio assets; it protects the overall creative labor a decompilation sets out to capture, even when the resulting code is entirely new and contains none of the original files. The same analysis argues decompilations should nonetheless be treated as fair use when their purpose is preserving a game that would otherwise become unplayable as hardware and support age out — a property-rights argument, drawing on John Locke's labor theory of ownership, for a fan's claim to keep access to something they already bought.

None of the current wave fits that preservation framing cleanly. Fallout: New York and the Modern Warfare 2 reconstruction are both still-supported, commercially available titles, not abandoned games rotting on unsupported hardware — the exact distinction the fair-use argument for decompilation depends on. A browser port of The Simpsons: Hit and Run, a 2003 game last patched two decades ago and not sold anywhere today, is a much closer fit for the preservation case than a GTA or Halo port is, even though all of them were swept up in the same viral post and the same wave of coverage.

That gap — publishers can get a specific upload removed in days, but nobody has tested whether the underlying act of AI-assisted decompilation is actually illegal — is the real story here. (Decompilation itself has a long, mostly-legal history in game preservation and interoperability research; what's new is not the legal theory but the speed. A process that used to require a specialist team months of manual reverse-engineering now runs unattended overnight.) Neither Activision nor Bethesda has sued anyone over this wave, and neither has gone after Anthropic or any other AI company — only the individual coders posting results, and only after those results went viral.

For now, the fight looks a lot like the early Napster era, just aimed at code instead of music files: publishers chasing individual uploads one at a time while the tool that makes them keeps getting better. The open question Kotaku's own reporting can't answer — whether AI-assisted decompilation is legal, legal-but-distributing-it-isn't, or neither — is exactly the one a publisher would have to bring a real lawsuit to settle, and so far, none has.