The Gaussian is enough: Toyota study finds non-Gaussian priors don't help fine-tuning LBMs

_krishna_murthy · x · 2026-09-25

A negative-result study from Toyota Research Institute, Woven by Toyota and Cornell ("The Gaussian Is Enough") shows that closer-to-target non-Gaussian action priors—which help when training imitation policies from scratch—offer no benefit when fine-tuning pretrained Large Behavior Models. Across 100K+ simulation rollouts on three LBM architectures (LBM 1.0, π0.5, GR00T N1.5), 40+ tasks, and 1250 hardware rollouts on five bimanual tasks, the standard Gaussian prior performed statistically indistinguishably or better, with a possible exception at very low fine-tuning data fractions. Diagnostic analyses indicate the observation encoder, not the action prior, governs fine-tuning performance.

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