NES emulator embedded in Qwen3.5-4B model weights
In brief
- A NES 6502 CPU emulator has been embedded in the weights of Qwen3.5-4B.
- ROMs like Super Mario Bros can be run inside the model, though very slowly.
- The project uses 15-year-old conformance tests to validate the emulation.
Drew Breunig embedded a Nintendo Entertainment System (NES) 6502 CPU emulator directly into the weights of the Qwen3.5-4B model. According to the announcement, it is now possible to run ROMs like Super Mario Bros inside Qwen, albeit very slowly.
The project builds on qwenputer by Divyansh Agrawal and relies on Opus 5.5 prompts for guidance. Drew Breunig used 15-year-old conformance tests released by Christopher Pow to validate the emulation. The goal was purely experimental, with no performance requirements.
This summary gives you the essentials. The full article, its figures and quotes are on Simon Willison's Weblog.
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