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Target Policy Optimization (arxiv.org)
1 point by t55 171 days ago | hide | past | pdf | discuss on HN

In plain words: It first picks the ideal mix of answers, boosting each one's odds by its score, then trains the model to match that mix so updates stop once it's reached. It matches standard score-driven training on easy tasks and does much better when rewards are rare.

Abstract

In RL, given a prompt, we sample a group of completions from a model and score them. Two questions follow: which completions should gain probability mass, and how should the parameters move to realize that change? Standard policy-gradient methods answer both at once, so the update can overshoot or undershoot depending on the learning rate, clipping, and other optimizer choices. We introduce \emph{Target Policy Optimization} (TPO), which separates the two questions. Given scored completions, TPO constructs a target distribution $q_i \propto p_i^{\,\mathrm{old}} \exp(u_i)$ and fits the policy to it by cross-entropy. The loss gradient on sampled-completion logits is $p^θ- q$, which vanishes once the policy matches the target. On tabular bandits, transformer sequence tasks, and billion-parameter LLM RLVR, TPO matches PG, PPO, GRPO, and DG on easy tasks and substantially outperforms them under sparse reward. Code is available at https://github.com/JeanKaddour/tpo.

Jean Kaddour
arXiv:2604.06159 · cs.LG · submitted Apr 7, 2026
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