New study traces late LM pretraining loss spikes to output-layer rounding errors

micahgoldblum · x · 2026-11-06

Work by Chen et al. traces late-emerging loss spikes in LM pretraining to rounding errors in the output layer: under high learning rates the output logit norm keeps growing until loss spikes. The paper also shows why three common fixes — z-loss, μ-centering, and momentum SGD — help through the same mechanism. Authors include Tom Goldstein, John Kirchenbauer, and Micah Goldblum.

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