让大模型一边生成答案一边自我评分,提升对齐效果。
URPO: A Unified Reward & Policy Optimization Framework for Large Language Models
- 将奖励模型与策略模型合一,在同一阶段共同优化。
- 在AlpacaEval上指令遵循得分提升至44.84,推理平均分达35.66。
- 适合追求高效对齐、减少训练流程复杂度的研究者。
大规模对齐流程通常将策略模型与独立训练的奖励模型配对,后者在强化学习中参数冻结,导致流程复杂且性能受限。本文提出统一奖励与策略优化框架(URPO),将指令遵循(“玩家”)与奖励建模(“裁判”)整合进单一模型和单次训练阶段。所有对齐数据——包括偏好对、可验证推理与开放指令——被统一转换为生成格式,并由单一的组相对策略优化(GRPO)循环优化。该方法使模型既能学习真实偏好与逻辑,又能为开放任务自动生成奖励。在Qwen2.5-7B模型上的实验表明,统一模型显著优于使用独立生成式奖励模型的强基线:AlpacaEval指令遵循得分从42.24提升至44.84,复合推理平均分从32.66增至35.66。此外,训练过程中自然形成更优的内部评估器,RewardBench得分为85.15,超过被替代的专用奖励模型(83.55)。通过消除独立奖励模型并促进生成与评估的协同进化,URPO提供了一条更简洁、高效、有效的语言模型对齐路径。
原文摘要 · Abstract (English)
Large-scale alignment pipelines typically pair a policy model with a separately trained reward model whose parameters remain frozen during reinforcement learning (RL). This separation creates a complex, resource-intensive pipeline and suffers from a performance ceiling due to a static reward signal. We propose a novel framework, Unified Reward & Policy Optimization (URPO), that unifies instruction-following ("player") and reward modeling ("referee") within a single model and a single training phase. Our method recasts all alignment data-including preference pairs, verifiable reasoning, and open-ended instructions-into a unified generative format optimized by a single Group-Relative Policy Optimization (GRPO) loop. This enables the model to learn from ground-truth preferences and verifiable logic while simultaneously generating its own rewards for open-ended tasks. Experiments on the Qwen2.5-7B model demonstrate URPO's superiority. Our unified model significantly outperforms a strong baseline using a separate generative reward model, boosting the instruction-following score on AlpacaEval from 42.24 to 44.84 and the composite reasoning average from 32.66 to 35.66. Furthermore, URPO cultivates a superior internal evaluator as a byproduct of training, achieving a RewardBench score of 85.15 and surpassing the dedicated reward model it replaces (83.55). By eliminating the need for a separate reward model and fostering a co-evolutionary dynamic between generation and evaluation, URPO presents a simpler, more efficient, and more effective path towards robustly aligned language models.
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