New FBT study: latent chains stay unused until RL length pressure forces them on

JohnCLangford · x · 2026-11-08

A new blog post investigates how effectively the Full Bandwidth Transformer (FBT) uses its latent chain of reasoning.
Key finding: FBT still prefers explicit CoT, but uses latents more when pressured with a length penalty.
John Langford: the post deeply addresses RL on an FBT; some problems show strong latent use enabling extrapolation, while for many problems FBT avoids latents entirely — new methods to encourage latent use may unlock more extrapolation.
The post also shares tricks for doing on-policy RL with FBT.

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