Copilot for piano: A 125M model that autocompletes live music on your phone

Think GitHub Copilot, but for live piano playing on your phone.

A developer built and open-sourced a 125M-parameter transformer model that autocompletes MIDI piano music in real time. Instead of burning multiple transformer passes to build a single note, the architecture processes pitch, timing, duration, and volume in a single step. The model runs locally at roughly 108 notes per second on an iPhone 15 inside a free app called RollTab.

Why it matters: On-device generative models usually lag behind live input. By rethinking MIDI tokenization—and baking sustain pedal logic directly into note durations—the developer got fluid, coherent music out of a tiny model without needing a cloud server.

If you have an iPhone or iPad and a MIDI keyboard, you can download RollTab for free to try it out.

Turns out the secret to real-time AI music isn't a massive data center—it's just smarter token math.