无需奖励模型,直接优化多目标冲突的文本生成。
Reward-free Alignment for Conflicting Objectives
- 基于成对偏好数据,用裁剪梯度法解决多目标冲突。
- 在多个大模型上实现更优的权衡表现,优于现有方法。
- 适合需要平衡多个对立目标的对齐任务,如安全与简洁性。
直接对齐方法被广泛用于将大语言模型(LLMs)与人类偏好对齐。然而,许多现实中的对齐问题涉及多个相互冲突的目标,简单聚合偏好会导致训练不稳定和权衡不佳。特别是加权损失方法可能无法找到同时提升所有目标的更新方向,而现有多目标方法通常依赖显式的奖励模型,增加复杂性并扭曲用户设定的偏好。本文贡献有二:第一,提出一种无奖励的冲突目标对齐框架RACO,直接利用成对偏好数据,通过一种新型裁剪型抗冲突梯度下降法解决梯度冲突,并提供收敛至满足用户指定权重的帕累托临界点的理论保证;进一步证明在双目标场景下裁剪可严格提升收敛速度。第二,引入若干启发式改进,并在多目标摘要与安全对齐任务上进行实验,验证该框架在Qwen 3、Llama 3、Gemma 3等多个大模型家族上的兼容性。定性和定量评估均表明,该方法在帕累托权衡上持续优于现有基线。
原文摘要 · Abstract (English)
Direct alignment methods are increasingly used to align large language models (LLMs) with human preferences. However, many real-world alignment problems involve multiple conflicting objectives, where naive aggregation of preferences can lead to unstable training and poor trade-offs. In particular, weighted loss methods may fail to identify update directions that simultaneously improve all objectives, and existing multi-objective approaches often rely on explicit reward models, introducing additional complexity and distorting user-specified preferences. The contributions of this paper are two-fold. First, we propose a Reward-free Alignment framework for Conflicted Objectives (RACO) that directly leverages pairwise preference data and resolves gradient conflicts via a novel clipped variant of conflict-averse gradient descent. We provide convergence guarantees to Pareto-critical points that respect user-specified objective weights, and further show that clipping can strictly improve convergence rate in the two-objective setting. Second, we improve our method using some heuristics and conduct experiments to demonstrate the compatibility of the proposed framework for LLM alignment. Both qualitative and quantitative evaluations on multi-objective summarization and safety alignment tasks across multiple LLM families (Qwen 3, Llama 3, Gemma 3) show that our method consistently achieves better Pareto trade-offs compared to existing multi-objective alignment baselines.
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