Claude and Codex agents decompiled a shooter, 83% exact

The headline number is 83%. The lesson is the test harness that produced it.

A developer says a team of Claude and Codex agents rebuilt a popular first-person shooter as C++ source over about three months, with most of it matching the original byte for byte. Other people are already shipping the results of the same trick into browsers.

What one developer says the agents did

Maurice Heumann wrote on his blog on Oct. 9 that 99% of the game's functions are now present in reconstructed source, and 83% compile to output identical to the original. He does not name the game, saying earlier posts about it came down after corporate pressure.

He ran Claude Max and Codex Pro subscriptions side by side, mostly on Sonnet 5, plus Opus 5.5 and models he names Luna, Sol and Terra, through the Claude Code and Codex command-line tools. The project started with four agents, three workers and a reviewer, and grew past 15.

He estimates 600 to 700 billion tokens. That is an estimate: he says the session logs were lost when the machines were wiped.

He says the rebuilt game runs without noticeable bugs and with all its original features. He will not release the code.

A locked test kept the agents honest

Heumann did not trust the agents to judge their own output. He built what he calls an oracle: a script that compiles each reconstructed function with the game's original compiler and compares the result against the shipped game. The answer is pass or fail.

Then he locked it. Inline assembly, patched object files and embedded bytes were banned, and CI checks a hash of the verification script against a stored secret so the agents cannot edit the test.

He explains why: "Agents have the desire to cheat if the assignment leaves room for interpretation."

His other lessons are blunt. Instructions fade as context gets compacted, so a scheduled job told the agents to reread them every hour. Bad output was cheaper to throw away than to fix. "Correctness is so much more important than productivity."

It's already spreading past one blog

Heumann's is the careful version. Kotaku's Lewis Parker reported on Oct. 9 that "hundreds of vibe-coded, AI-decompiled emulators and games" have appeared in the past couple of weeks, including browser ports of Halo: CE and GTA: Vice City. He counted four different browser ports of Halo: CE alone. Kotaku reported no publisher response.

That is the copyright fight coming, and it will not stay in games. Any shipped binary is now a much cheaper target.

Copy his harness for your own agent jobs

If you run long AI agent jobs, copy his structure. A machine-checkable definition of done. A test the agent cannot touch. Instructions repeated on a timer. Permission to delete and redo.

If you ship software as compiled code, assume that reconstructing your source has gotten cheaper. Your license terms and your server-side logic matter more than they did a year ago.

The first takedown is the next signal

Watch for the first takedown notice or lawsuit aimed at an AI-decompiled port, and for which publisher sends it.

Build the oracle before you hire the agents.