Drew Breunig built an emulator for the Nintendo Entertainment System’s 6502 CPU into the weights of Qwen3.5-4B, the model’s learned parameters. Simon Willison reports that it can run NES ROMs, including Super Mario Bros., though very slowly.
Breunig said he used prompts with Opus 5.5 to explore the idea and build a version that could run from model weights and a command-line tool. The work also used NES CPU conformance tests released by Christopher Pow.
Why it matters
For people curious about running old games with AI models, this shows an NES CPU can be represented in model weights, but the reported slow speed limits its use for playing games.
