Measured product lead custody receipt.
Polymath LLM Training On Mobile Phone
On-device language-model training research lane · Polymath-AI · PyPI 0.1.0 · Snapdragon 8 Elite target
Polymath-AI is a training harness aimed at the Snapdragon 8 Elite (SM8750) phone chip. It trains only the first and last layers of a language model while the middle stays sealed and SHA-checked. The host smoke runs cleanly on Qwen 2.5 1.5B with the frozen middle showing zero weight changes.
Phone compilation, licensed multilingual corpora, sustained device telemetry, and a public checkpoint are all open. This is a route, not a product.

“Training a language model on a phone still has no measured path from corpus to battery.”
A training harness, not a finished model.
Mobile language-model work usually means inference on the chip, with training kept in the cloud. The conventional route ships a trained model down to the device and never lets it learn there.
Polymath trains only the boundary layers of a language model — layer 0, the final layer, and the language-model head — while every middle layer stays sealed and SHA-checked at frozen_changes = 0. Host smoke passes on Qwen 2.5 1.5B, with loss falling from 14.515 to 4.449 in five steps and the middle bit-identical across the run.
Host smoke passes, phone compile remains unsupported.
Frozen middle stays bit-stable while boundary layers train.
Only the named boundary layers receive gradient updates — layer 0, the final layer, and the language-model head. The middle layers' weights are SHA-checked before and after every training pass; if any frozen weight moves, the run halts immediately and reports the offending tensor.
The unit of bit-exactness is per-pass, host-side. Five steps on Qwen 2.5 1.5B leave the frozen middle unchanged across the entire run. No on-device determinism claim is made yet; the Qualcomm Neural Network and LiteRT paths are not exercised.
QNN/LiteRT compile on the Snapdragon 8 Elite is measured unsupported, so the scheduler cannot reach the device yet. On-device execution, sustained telemetry, licensed-corpus ingestion, and the next PyPI release all remain open. Tokenization currently bloats Zulu 2.68× and Greek 4.38× past target. No phone-trained model or public checkpoint exists.
FIVE PATHS FROM ONE phone-side training loop.
The hinge is selective continual pretraining under real mobile constraints. Polymath-AI does not promise a finished model. It builds the scheduler, corpus discipline, and frozen-middle guarantee needed to answer one question honestly — whether training a useful language model on a phone, under battery and thermal limits, is worth doing at all.