Reproduce “DIAL-OPD: Learning More from Fewer Tokens in On-Policy Distillation” on OpenResearch

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About this paper

Anhao Zhao, Haoran Xin, Junlong Tong, Yingqi Fan, Xuan Lu, Ping Nie, Wenjie Li, Xiaoyu Shen

DIAL-OPD selects which student-generated tokens contribute to on-policy distillation loss, using both teacher–student disagreement and the probabilities’ absolute scale. This sampled-token approach avoids full-vocabulary probabilities, while retaining all tokens in context. In tested Qwen3 math experiments, retaining 40% of response positions improved seven-benchmark mean accuracy over full-token Vanilla OPD, with a largest reported gain of 5.25 percentage points; this does not establish lower training time or compute.

Key insights

  • In the tested settings, sparse supervision could outperform dense supervision: random retention at several rates beat full-token OPD in an initial experiment.
  • Large log-ratio rewards can be misleading when both models assign a token low probability; at 10% retention, low-low tokens made up 20.59% of selected tokens but 49.80% of their absolute reward.
  • Moderate probability weighting worked better than either ignoring probability scale or applying it too strongly; the best β varied by student size.

Summary by alphaXiv.

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