arXiv:2606.01382cs.LGcs.AI2026-06

提出新方法提升大模型偏好对齐效率,解决传统方法探索不足问题。

Efficient Exploration for Iterative Nash Preference Optimization

  • 显式引入探索机制,结合SFT正则与对抗策略优化
  • 实现O(√T) regret bound,避免对KL参数的指数依赖
  • 适用于大模型微调,实测优于现有NLHF基线

偏好对齐是提升大语言模型性能的核心,但传统基于奖励的范式在人类偏好存在循环性、非传递性时受限。纳什学习人类反馈(NLHF)将对齐建模为偏好博弈,以纳什均衡为目标,而非单纯最大化奖励。然而,可扩展NLHF的学习理论基础仍有限:现有后悔界依赖于需估计通用偏好模型的预言机方法,并求解带KL正则化的极小极大问题;而迭代式NLHF直接优化策略级偏好损失,实现更简单但缺乏后悔保证。本文研究一般偏好模型下的在线迭代NLHF,发现探索是关键障碍。首先,证明标准迭代NLHF可能随KL正则化参数呈指数依赖,表明仅靠策略更新带来的隐式探索不足以控制后悔。其次,提出一种显式探索的迭代NLHF算法,融合SFT正则与对抗策略探索,保持直接策略优化结构,无需显式估计偏好模型,且实现无指数依赖的$O(\sqrt{T})$后悔界。若具备极小极大预言机,后悔可进一步降至$O(\log(T))$,揭示了学习一般偏好博弈中的计算-统计权衡。最后,在\texttt{Llama-3-8B-Instruct}上验证该方法,多基准测试中显式探索带来持续改进。

原文摘要 · Abstract (English)

Preference alignment is central to improving large language models, but standard reward-based formulations can be restrictive when human preferences are cyclic, non-transitive, or otherwise not representable by a scalar reward. Nash Learning from Human Feedback (NLHF) addresses this limitation by modeling alignment as a preference game and targeting a Nash equilibrium rather than a reward maximizer. However, the learning-theoretic foundations of scalable NLHF remain limited. Existing regret guarantees rely on oracle-based methods that estimate a general preference model and solve KL-regularized minimax problems, while iterative NLHF methods directly optimize policy-level preference losses and are easier to implement but lack regret guarantees. We study online iterative NLHF under general preference models and identify exploration as the key obstacle. First, we show that standard iterative NLHF can suffer an exponential dependence on the KL-regularization parameter, revealing that implicit exploration through policy updates is insufficient for controlling regret. Second, we propose an explicitly exploratory iterative NLHF algorithm that combines SFT-based regularization with adversarial policy exploration. The resulting method retains the direct policy optimization structure of iterative NLHF, avoids explicit preference model estimation, and achieves an $O(\sqrt{T})$ regret bound without an exponential dependence on the KL-regularization parameter. We show that the regret can be improved to $O(\log(T))$ with access to a minimax oracle, clarifying the computational-statistical tradeoff in learning general preference games. Finally, we instantiate our method for LLM fine-tuning and evaluate it on \texttt{Llama-3-8B-Instruct} across multiple benchmarks, where explicit exploration yields consistent improvements over existing NLHF baselines.

偏好对齐纳什均衡大模型微调强化学习

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