# Sign-Based Optimizers Are Effective Under Heavy-Tailed Noise

arXiv: https://arxiv.org/abs/2602.07425 · HTML: https://mlsanity.com/paper/2602.07425/

## Key facts

- Cited by 15 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 7 Feb 2026.

## Built on by (most cited first, 15 of 15)

- [The Newton-Muon Optimizer](https://mlsanity.com/paper/2604.01472/) (2026)
- [Muon is Not That Special: Random or Inverted Spectra Work Just as Well](https://mlsanity.com/paper/2605.11181/) (2026)
- [StoSignSGD: Unbiased Structural Stochasticity Fixes SignSGD for Training Large Language Models](https://mlsanity.com/paper/2604.15416/) (2026)
- [MiMuon: Mixed Muon Optimizer with Improved Generalization for Large Models](https://mlsanity.com/paper/2605.19619/) (2026)
- [When and Why SignSGD Outperforms SGD: A Theoretical Study Based on ℓ1-norm Lower Bounds](https://mlsanity.com/paper/2605.06615/) (2026)
- [Tight Complexity of Muon under Heavy-Tailed Noise](https://mlsanity.com/paper/2605.18528/) (2026)
- [LionMuon: Alternating Spectral and Sign Descent for Efficient Training](https://mlsanity.com/paper/2605.19811/) (2026)
- [The Convergence Behavior of Adam under Heavy-Tailed Noise](https://mlsanity.com/paper/2607.27383/) (2026)
- [Schattor: Schatten-family methods for deep learning optimization](https://mlsanity.com/paper/2606.15702/) (2026)
- [Open Problem: Is AdamW Effective Under Heavy-Tailed Noise?](https://mlsanity.com/paper/2606.23676/) (2026)
- [Second-Moment Memory in Coordinatewise Adam](https://mlsanity.com/paper/2608.15824/) (2026)
- [CLion: Efficient Cautious Lion Optimizer with Enhanced Generalization](https://mlsanity.com/paper/2604.14587/) (2026)
- [LionMuon: Alternating Spectral and Sign Descent for Efficient Training](https://mlsanity.com/paper/2609.35297/) (2026)
- [From Parallel to Sequential: Small-Batch Noise Restores Simplicity Bias of Muon](https://mlsanity.com/paper/2610.16868/) (2026)
- [Memory-Efficient Subspace Optimization with Residual Correction: From Momentum SGD to Muon](https://mlsanity.com/paper/2610.19844/) (2026)

## Abstract (arXiv)

While adaptive gradient methods are the workhorse of modern machine learning, sign-based optimization algorithms such as Lion and Muon have recently demonstrated superior empirical performance over AdamW in training large language models (LLM). However, a theoretical understanding of why sign-based updates outperform variance-adapted methods remains elusive. In this paper, we aim to bridge the gap between theory and practice through the lens of heavy-tailed gradient noise, a phenomenon frequently observed in language modeling tasks. Theoretically, we introduce a novel generalized heavy-tailed noise condition that captures the behavior of LLMs more accurately than standard finite variance assumptions. Under this noise model, we establish sharp convergence rates of SignSGD and Lion for generalized smooth function classes, matching or surpassing previous best-known bounds. Furthermore, we extend our analysis to Muon and Muonlight, providing what is, to our knowledge, the first rigorous analysis of matrix optimization under heavy-tailed stochasticity. These results offer a strong theoretical justification for the empirical superiority of sign-based optimizers, showcasing that they are naturally suited to handle the noisy gradients associated with heavy tails. Empirically, LLM pretraining experiments validate our theoretical insights and confirm that our proposed noise models are well-aligned with practice.