Muon Does Not Converge on Convex Lipschitz Functions

Fuente: arXiv
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Autores principales: Parshakova, Tetiana, Khaled, Ahmed, Crawshaw, Michael, Garrigos, Guillaume, Gower, Robert M.
Formato: Preprint
Publicado: 2026
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author Parshakova, Tetiana
Khaled, Ahmed
Crawshaw, Michael
Garrigos, Guillaume
Gower, Robert M.
author_facet Parshakova, Tetiana
Khaled, Ahmed
Crawshaw, Michael
Garrigos, Guillaume
Gower, Robert M.
contents Muon and its variants have shown strong empirical performance in a variety of deep learning tasks. Existing convergence analyses of Muon rely on smoothness assumptions, though arguably the most successful function class for developing deep learning methods (such as AdaGrad, Shampoo, Schedule-Free and more) has been the class of convex and Lipschitz functions. In this paper we question whether the classical convex Lipschitz model is a useful one for understanding Muon. Our answer is no. We show that Muon does not converge on the class of convex and Lipschitz functions, regardless of the choice of learning rate schedule. We also show that error feedback restores convergence of Muon and all the non-Euclidean subgradient methods with momentum. However, this theoretical fix using error feedback degrades the performance of Muon in two representative settings for image classification (CIFAR-10) and language modeling (nanoGPT on FineWeb-Edu 10B). Our conclusion is that convex Lipschitz theory, despite having a prominent role in the design of practical methods for deep learning, is not the most suited one for Muon. This suggests that Muon's success must come from structure absent from this model, most plausibly related to smoothness.
format Preprint
id arxiv_https___arxiv_org_abs_2605_08980
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Muon Does Not Converge on Convex Lipschitz Functions
Parshakova, Tetiana
Khaled, Ahmed
Crawshaw, Michael
Garrigos, Guillaume
Gower, Robert M.
Machine Learning
Optimization and Control
Muon and its variants have shown strong empirical performance in a variety of deep learning tasks. Existing convergence analyses of Muon rely on smoothness assumptions, though arguably the most successful function class for developing deep learning methods (such as AdaGrad, Shampoo, Schedule-Free and more) has been the class of convex and Lipschitz functions. In this paper we question whether the classical convex Lipschitz model is a useful one for understanding Muon. Our answer is no. We show that Muon does not converge on the class of convex and Lipschitz functions, regardless of the choice of learning rate schedule. We also show that error feedback restores convergence of Muon and all the non-Euclidean subgradient methods with momentum. However, this theoretical fix using error feedback degrades the performance of Muon in two representative settings for image classification (CIFAR-10) and language modeling (nanoGPT on FineWeb-Edu 10B). Our conclusion is that convex Lipschitz theory, despite having a prominent role in the design of practical methods for deep learning, is not the most suited one for Muon. This suggests that Muon's success must come from structure absent from this model, most plausibly related to smoothness.
title Muon Does Not Converge on Convex Lipschitz Functions
topic Machine Learning
Optimization and Control
url https://arxiv.org/abs/2605.08980