Drew Breunig’s nesformer runs an NES CPU emulator inside Qwen3.5-4B weights
dbreunig/nesformer
- Who
- Drew Breunig
- What
- built a working Nintendo Entertainment System 6502 CPU emulator in Qwen3.5-4B weights
- Quote
Drew Breunig baked a working emulator for a Nintendo Entertainment System 6502 CPU into the weights of Qwen3.5-4B.
What happened
Simon Willison reports that Drew Breunig built a working Nintendo Entertainment System 6502 CPU emulator into Qwen3.5-4B’s weights, allowing NES ROMs such as Super Mario Bros to run very slowly inside Qwen. Inspired by Divyansh Agrawal’s qwenputer, Breunig shared the Opus 5.5 prompts used to build it. Opus apparently found and used NES CPU conformance tests released 15 years ago by Christopher Pow.
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See the full storyDrew Breunig Builds an NES CPU Emulator into Qwen3.5-4B’s WeightsThe story so far
Drew Breunig built a working Nintendo Entertainment System 6502 CPU emulator into Qwen3.5-4B’s weights, allowing NES ROMs such as Super Mario Bros. to run very slowly inside Qwen, Simon Willison reported. Breunig’s project, nesformer, was inspired by Divyansh Agrawal’s qwenputer. Breunig shared the Opus 5.5 prompts used to build it; according to Willison, Opus apparently found and used NES CPU conformance tests that Christopher Pow released 15 years ago.
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