Rethinking Language Model Scaling under Transferable Hypersphere Optimization

TL;DR

This paper introduces HyperP, a hypersphere optimization framework for large language models that enables stable, efficient transfer of hyperparameters across scales and architectures, improving training stability and performance.

Contribution

HyperP is the first framework to transfer optimal learning rates across model scales under the Frobenius-sphere constraint using the Muon optimizer, enhancing stability and efficiency.

Findings

A single base learning rate transfers across scales, improving compute efficiency by 1.58×.

HyperP maintains bounded instability indicators during training at various scales.

SqrtGate improves MoE gating stability and expert balance under hypersphere constraints.

Abstract

Scaling laws for large language models depend critically on the optimizer and parameterization. Existing hyperparameter transfer laws are mainly developed for first-order optimizers, and they do not structurally prevent training instability at scale. Recent hypersphere optimization methods constrain weight matrices to a fixed-norm hypersphere, offering a promising alternative for more stable scaling. We introduce HyperP (Hypersphere Parameterization), the first framework for transferring optimal learning rates across model width, depth, training tokens, and Mixture-of-Experts (MoE) granularity under the Frobenius-sphere constraint with the Muon optimizer. We prove that weight decay is a first-order no-op on the Frobenius sphere, show that Depth-$\mu$P remains necessary, and find that the optimal learning rate follows the same data-scaling power law with the "magic exponent" 0.32 previously observed for AdamW. A single base learning rate tuned at the smallest scale transfers across all compute budgets under HyperP, yielding $1.58\times$ compute efficiency over a strong Muon baseline at $6\times10^{21}$ FLOPs. Moreover, HyperP delivers transferable stability: all monitored instability indicators, including $Z$-values, output RMS, and activation outliers, remain bounded and non-increasing under training FLOPs scaling. We also propose SqrtGate, an MoE gating mechanism derived from the hypersphere constraint that preserves output RMS across MoE granularities for improved granularity scaling, and show that hypersphere optimization enables substantially larger auxiliary load-balancing weights, yielding both strong performance and good expert balance. We release our training codebase at https://github.com/microsoft/ArchScale.