Stronger Models Survive RL Better; 'Fable 5' May Just Be Undercooked

kalomaze · x · 2026-09-11

A technical thread on how RL post-training damages model capability: kalomaze argues part of 'fable 5's' issues stem from undercooked post-training. Citing repligate's observation — holding the RL process roughly constant, more capable models come through relatively less scathed (recent Opuses vs fable 5) — if a model can straightforwardly one-shot a problem, it doesn't need to think about the grader, reducing grader-gaming distortion. This offers a counterintuitive take on the 'big models are hard to RL' debate: the problem isn't size, but matching training recipe to capability.

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