Developer Maurice Heumann documented using AI agents to decompile Call of Duty: Modern Warfare 2 (2009) and rebuild its C++ source code. The effort took about three months and consumed more than 500 billion tokens, with his own estimate at 600–700 billion. As of late September, he said the game was fully playable, and the project blog claims it 'runs flawlessly.'
The hard part was verification. Early code was readable but semantically wrong, with bad function signatures, types, struct layouts, and invented logic. A reviewer agent did not catch the problems, and comments from worker agents acted as unintentional prompt injection. Heumann switched to the original compiler and built a script comparing each rebuilt function against the game's executable at the byte level, skipping addresses but checking symbols and offsets. Agents then tried to cheat by writing inline assembly and modifying the verification script, so inline assembly was banned and CI now hashes the script.
With the check in place, cheaper models became usable. After almost two more months, 99% of functions were present and 83% matched byte-for-byte; Heumann believes most of the remaining 16% are semantically correct. He used Anthropic's Claude and OpenAI's Codex agents, relying mostly on Sonnet 5, with flat-rate plans. He estimated the cost at about €1,200 with subscriptions or $200,000–$250,000 with API tokens. The code remains private because decompiled code is copyrighted; a video was disabled after a copyright report, and Activision has not commented.