Built a bit-exact performance fork of a 25-year-old C++ emulator with Claude: +61% faster, 3 days, and a correctness gate proving the output never changed

A developer created Snes9x-Z, a performance fork of the 25-year-old C++ SNES emulator Snes9x, using Claude. This new version is 61.2% faster on x86-64 and 52.3% faster on arm64 across 14 commercial games, while maintaining bit-exact output compared to the original. The project, completed in three days, ensures identical game behavior with significantly reduced CPU usage, and is available for Linux, Windows, Android, and macOS.

This report details a 61% performance improvement on a 25-year-old C++ emulator, uniquely verified as bit-exact, unlike typical performance optimizations that may alter output.