CMU paper shows pretraining, SFT and RL can run as one unified likelihood-based algorithm

omarsar0 · x · 2026-11-01

A CMU-led paper (with JHU and Aurora Innovation) argues the staged pipeline of pretraining, midtraining, SFT and RL is not fundamental. By deriving suitable RL objectives as maximum-likelihood fitting to model-generated targets, all stages share one loss and one trainer — dubbed unified training. Design reduces to choosing which data, in what proportions and when; staged training becomes a special case. A 124M model trained from scratch on reasoning puzzles beat staged training on RL tasks and generalized to larger unseen puzzles, reusing the midtraining corpus up to 4 times.

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