Paper
Demystifying Reinforcement Learning for Long-Horizon Tool-Using Agents: A Comprehensive Recipe
Authors
Xixi Wu, Qianguo Sun, Ruiyang Zhang, Chao Song, Junlong Wu, Yiyan Qi, Hong Cheng
Abstract
Reinforcement Learning (RL) is essential for evolving Large Language Models (LLMs) into autonomous agents capable of long-horizon planning, yet a practical recipe for scaling RL in complex, multi-turn environments remains elusive. This paper presents a systematic empirical study using TravelPlanner, a challenging testbed requiring tool orchestration to satisfy multifaceted constraints. We decompose the agentic RL design space along 5 axes: reward shaping, model scaling, data composition, algorithm selection, and environmental stability. Our controlled experiments yield 7 key takeaways, e.g., (1) reward and algorithm choices are scale-dependent as smaller models benefit from staged rewards and enhanced exploration, whereas larger models converge efficiently with simpler dense rewards, (2) ~ 1K training samples with a balanced difficulty mixture mark a sweet spot for both in-domain and out-of-domain performance, and (3) environmental stability is critical to prevent policy degradation. Based on our distilled recipe, our RL-trained models achieve state-of-the-art performance on TravelPlanner, significantly outperforming leading LLMs.
Metadata
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Raw Data (Debug)
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"raw_xml": "<entry>\n <id>http://arxiv.org/abs/2603.21972v1</id>\n <title>Demystifying Reinforcement Learning for Long-Horizon Tool-Using Agents: A Comprehensive Recipe</title>\n <updated>2026-03-23T13:40:08Z</updated>\n <link href='https://arxiv.org/abs/2603.21972v1' rel='alternate' type='text/html'/>\n <link href='https://arxiv.org/pdf/2603.21972v1' rel='related' title='pdf' type='application/pdf'/>\n <summary>Reinforcement Learning (RL) is essential for evolving Large Language Models (LLMs) into autonomous agents capable of long-horizon planning, yet a practical recipe for scaling RL in complex, multi-turn environments remains elusive. This paper presents a systematic empirical study using TravelPlanner, a challenging testbed requiring tool orchestration to satisfy multifaceted constraints. We decompose the agentic RL design space along 5 axes: reward shaping, model scaling, data composition, algorithm selection, and environmental stability. Our controlled experiments yield 7 key takeaways, e.g., (1) reward and algorithm choices are scale-dependent as smaller models benefit from staged rewards and enhanced exploration, whereas larger models converge efficiently with simpler dense rewards, (2) ~ 1K training samples with a balanced difficulty mixture mark a sweet spot for both in-domain and out-of-domain performance, and (3) environmental stability is critical to prevent policy degradation. Based on our distilled recipe, our RL-trained models achieve state-of-the-art performance on TravelPlanner, significantly outperforming leading LLMs.</summary>\n <category scheme='http://arxiv.org/schemas/atom' term='cs.LG'/>\n <category scheme='http://arxiv.org/schemas/atom' term='cs.CL'/>\n <published>2026-03-23T13:40:08Z</published>\n <arxiv:comment>Codes are available at https://github.com/WxxShirley/Agent-STAR</arxiv:comment>\n <arxiv:primary_category term='cs.LG'/>\n <author>\n <name>Xixi Wu</name>\n </author>\n <author>\n <name>Qianguo Sun</name>\n </author>\n <author>\n <name>Ruiyang Zhang</name>\n </author>\n <author>\n <name>Chao Song</name>\n </author>\n <author>\n <name>Junlong Wu</name>\n </author>\n <author>\n <name>Yiyan Qi</name>\n </author>\n <author>\n <name>Hong Cheng</name>\n </author>\n </entry>"
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