Drew Breunig embeds NES emulator in Qwen3.5-4B weights

Drew Breunig baked a working Nintendo Entertainment System 6502 CPU emulator into the weights of Qwen3.5-4B, enabling very slow playback of NES ROMs such as Super Mario Bros inside the model. He disclosed the Opus 5.5 prompts used to build the system.

Why it matters

Benchmark your product’s in‑model emulation against the NES emulator built into Qwen3.5‑4B; users may expect novel in‑LLM functionalities.

For product managers

For your product

What does this mean for your product?

Try it on your product

Read at Simon Willison

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