muP Lets You Tune Hyperparameters on a Small Model and Transfer to Giant Ones

RobertTLange · x · 2026-11-13

Robert Lange breaks down the Tensor Programs V paper: under standard parametrization, a learning rate tuned on a small model fails at larger widths — updates grow with width and the tuned η diverges.

μP (Maximal Update Parametrization) scales η per layer with width so update size stays constant, enabling muTransfer: tune on a small proxy model, then zero-shot transfer HPs to the full-sized model. Verified on Transformers and ResNets: HPs transferred from a 13M model beat published BERT-large (350M) numbers; transferring from 40M beats published 6.7B GPT-3 results at only 7% of total pretraining cost in tuning. Open-sourced via pip install mup.

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