NES emulator embedded in Qwen3.5-4B weights
In brief
- An NES 6502 emulator is embedded in Qwen3.5-4B weights.
- ROMs like Super Mario Bros can be executed, but very slowly.
- The project uses conformance tests published in 2011 by Christopher Pow.
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 NES ROMs like Super Mario Bros inside the model, albeit very slowly.
The project builds on previous work such as Divyansh Agrawal's qwenputer. Drew Breunig used Opus 5.5 prompts to design the system and relied on a suite of NES CPU conformance tests published 15 years ago by Christopher Pow. The goal was primarily experimental, with no immediate 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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