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arXiv · 2609.06100

VERPO: Verified Evidence Regularized Policy Optimization

Haijiang Li·Chengyu Lv·Yi Zhang·Zhibing Zhang·Rui Qian·Yuchen Zhang·Xiaofan Zhang·Mingshan Wang·Xiaofei Jing·Yu Tong·Cangqi Zhou
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Abstract

Verifiable outcome rewards guide language-model post-training, but sequence-level advantages do not identify which token-level decisions should be preserved or revised. Evidence-conditioned Teachers provide denser supervision by replaying sampled trajectories with privileged feedback. Yet indiscriminate imitation risks transferring formatting or reasoning-style shifts that do not support task success. We introduce VERPO, a Verified Evidence Regularized Policy Optimization framework that treats evidence as a proposal for policy correction while retaining the outcome objective. It separates evidence-free reference restoration from signed token-level evidence corrections. Fisher Evidence Contrast attenuates corrections along an estimated evidence-presence direction. A stopped token-wise ZPD controller scales acceptance according to local reward alignment and Fisher movement cost, while the reference channel remains independent of acceptance. Across five scientific-reasoning and tool-use tasks, the best variant on each backbone exceeds the strongest compared baseline in average score. The averages rise from 0.6826 to 0.6857 on Qwen3-4B, from 0.6895 to 0.7058 on Qwen3-8B, and from 0.4751 to 0.5657 on Llama-3.2-1B.

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Haijiang Li, Chengyu Lv, Yi Zhang, Zhibing Zhang, Rui Qian, Yuchen Zhang, Xiaofan Zhang, Mingshan Wang, Xiaofei Jing, Yu Tong, Cangqi Zhou. 2026-09-05. VERPO: Verified Evidence Regularized Policy Optimization. https://arxiv.org/abs/2609.06100

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