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Pass@k is ubiquitous in evaluating reasoning models, but the metric is more subtle than it appears. Computing it correctly requires the unbiased estimator, and the nonlinearity of pass@k means it effectively upweights hard problems compared to pass@1.
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A training-free approach to process rewards: estimate V(prefix) via log-probability, compute marginal utility across episodes. Plus VeRL implementation pitfalls to avoid.
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On-policy distillation integrates teacher guidance into RL training, but the implementation is full of silent failures. This post documents the architecture, pitfalls, and design choices from building OPD in VeRL.
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An empirical investigation into what drives output length growth during RL training, revealing that dataset difficulty composition is the primary driver behind the ‘overthinking’ phenomenon.