StepSearch: Igniting LLMs Search Ability via Step-Wise Proximal Policy Optimization

• URL: http://arxiv.org/abs/2505.15107v2
• Date: Mon, 26 May 2025 04:44:21 GMT
• Title: StepSearch: Igniting LLMs Search Ability via Step-Wise Proximal Policy Optimization
• Abstract summary: StepSearch is a framework for search LLMs that trained with step-wise proximal policy optimization method.<n>It consists of richer and more detailed intermediate search rewards and token-level process supervision based on information gain and redundancy penalties.<n>On standard multi-hop QA benchmarks, it significantly outperforms global-reward baselines, achieving 11.2% and 4.2% absolute improvements for 3B and 7B models.
• Score: 14.931231544839687
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Efficient multi-hop reasoning requires Large Language Models (LLMs) based agents to acquire high-value external knowledge iteratively. Previous work has explored reinforcement learning (RL) to train LLMs to perform search-based document retrieval, achieving notable improvements in QA performance, but underperform on complex, multi-hop QA resulting from the sparse rewards from global signal only. To address this gap in existing research, we introduce StepSearch, a framework for search LLMs that trained with step-wise proximal policy optimization method. It consists of richer and more detailed intermediate search rewards and token-level process supervision based on information gain and redundancy penalties to better guide each search step. We constructed a fine-grained question-answering dataset containing sub-question-level search trajectories based on open source datasets through a set of data pipeline method. On standard multi-hop QA benchmarks, it significantly outperforms global-reward baselines, achieving 11.2% and 4.2% absolute improvements for 3B and 7B models over various search with RL baselines using only 19k training data, demonstrating the effectiveness of fine-grained, stepwise supervision in optimizing deep search LLMs. Our code will be released on https://github.com/Zillwang/StepSearch.

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