Process Reward Models
Also known as PRM
Overview
Process reward models estimate whether intermediate steps in a reasoning chain or agent trajectory are valid, useful, and moving toward a goal, rather than judging only the final answer. They are trained from human step labels, formal or execution-based checks, rubrics, and signals inferred from successful or failed outcomes; some methods avoid a separate model and derive rewards from rollouts or internal probabilities. These rewards support reinforcement learning and test-time methods such as reranking, beam search, and tree search across math, coding, retrieval, multimodal, and agent tasks. A central challenge is that noisy or miscalibrated step scores can compound errors or be exploited, and it remains difficult to make process evaluation reliable across domains and task settings.
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