The paper investigates how reward models, used for preference optimization and ranking, can be biased by prompt-specific effects that are not captured by pairwise evaluation. By comparing between‑prompt variance in model scores to human ratings, the authors find that reward scores cluster strongly by prompt, often more so than human judgments. They propose a human‑referenced audit that examines between‑prompt variation, sensitivity to incorrect prompts, and usefulness for response selection, and demonstrate that adjusting for prompt means can reduce misleading global selection of responses.
By Mateusz Modrzejewski, Tomasz Radzikowski
arXiv:2609.36652v1 Announce Type: new
Abstract: Open-ended generation lacks canonical answers, making pointwise rewards difficult to calibrate for group-based reinforcement learning. Directly ranking...
By Zixuan Yang, Yiqun Chen, Qi Liu, Wei Yang, Erhan Zhang, Liyi Chen, Qimeng Wang, Yan Gao, Jiaxin Mao
arXiv:2608.30005v1 Announce Type: new
Abstract: Rubric-based reinforcement learning extends RL beyond tasks with exact answers or rule-based verifiers by scoring responses against instance-specific c...
By Fengyu Xie, Yilun Zhao, Bingsen Chen, Arman Cohan, Chen Zhao
arXiv:2604. 07343v2 Announce Type: replace-cross Abstract: Pluralistic alignment has emerged as a critical frontier in the development of Large Language Models (LLMs), with reward models (RMs) serving as a central mechanism for capturing diverse human values.
By Qiyao Ma, Dechen Gao, Rui Cai, Boqi Zhao, Hanchu Zhou, Junshan Zhang, Zhe Zhao
arXiv:2610.05370v2 Announce Type: replace
Abstract: Generative reward models (GRMs) are important for LLM optimization. Unlike scalar reward models, GRMs generate natural-language critiques alongside...
By Xuancheng Li, Beining Wang, Haitao Li, Heng Wang, Yujia Zhou, Qingyi Pan, Blaze Chen, Yiqun Liu, Min Zhang, Qingyao Ai
PerSPL (Personalized Semi-supervised Preference Learning) is a backbone‑agnostic framework that stabilizes cross‑prompt score coordinates using pair‑mean score centering, enabling the conversion of unlabeled responses into user‑specific training signals. It addresses the scarcity of user‑specific preference comparisons by leveraging large pools of unlabeled responses, which are otherwise unused by existing personalized reward models. Across four benchmarks—PersonalLLM, HelpSteer2, Reddit TLDR, and Chatbot Arena—PerSPL achieves the highest mean accuracy for both seen and unseen users, demonstrating its effectiveness in summarization and open‑domain chatbot interaction settings.
By Xiaoan Xu, Tingzhou Wei, Juncheng Dong, Korel Gundem, Ethan X. Fang, Zhengling Qi