RAGEN: Understanding Self-Evolution in LLM Agents via Multi-Turn Reinforcement Learning
Paper · 2025 · Zihan Wang, Kangrui Wang, Qineng Wang et al.
Summary
The paper asks how LLM agents can be trained with reinforcement learning to improve through their own experience in interactive settings. Unlike single-turn math or coding, these settings involve many turns and noisy environment responses. The authors define StarPO, a framework that optimizes whole agent trajectories (observations, thinking traces, actions, rewards) with either PPO or GRPO. They also release RAGEN, a modular open-source system covering rollout generation, reward assignment and policy updates. Experiments use four environments: Bandit, Sokoban, Frozen Lake and WebShop. They show that multi-turn agent RL often falls into an "Echo Trap". In this collapse, reward variance shrinks, entropy drops and gradients spike. A stabilized variant, StarPO-S, counters this by filtering trajectories, adding a critic baseline and decoupling clipping. Further analysis shows that rollout design and reward design strongly affect learning. When rewards reflect only the final outcome, explicit reasoning tends to fade or becomes hallucinated. The work matters because it offers both reusable infrastructure and practical design guidance for stable agent RL.
Key points
- StarPO (State-Thinking-Actions-Reward Policy Optimization) treats a full multi-turn trajectory as the unit of optimization. In each turn the model writes
<think>…</think><answer>…</answer>output, and the framework supports both critic-based PPO and critic-free GRPO. - The four test environments span different challenges:
- Bandit: single-turn and stochastic.
- Sokoban: multi-turn and deterministic.
- Frozen Lake: multi-turn and stochastic.
- WebShop: multi-turn and open-domain.
- A semantically reversed BanditRev variant is also studied.
- StarPO-S reduces Echo Trap instability through three changes: it keeps trajectories selected by how much they vary, uses a critic as a baseline, and applies clipping in a decoupled manner.
- Rollout design helps training in three ways:
- Start from diverse initial states and sample several responses for each.
- Allow multiple actions per turn.
- Refresh rollouts often. In the Online-k experiments (k = 1, 2, 5, 10), the lowest reuse, Online-1, converged better.
- Reasoning in multi-turn tasks shrinks over training, and no-think variants often match or beat thinking ones. The authors suggest format penalties and finer-grained rewards as remedies. They list small-scale tasks, no replay buffers and no multimodal tasks as limitations.
Fields, topics and concepts
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksArts and Humanities · 17,450 worksLanguage and Linguistics · 17,296 works
Cite
Cite as Zihan Wang, Kangrui Wang, Qineng Wang, Pingyue Zhang, Linjie Li, Zhengyuan Yang, Xing Jin, Kefan Yu, Minh Nhat Nguyen, Licheng Liu, Eli Gottlieb, Yiping Lu, Kyunghyun Cho, Jiajun Wu, Li Fei-Fei, Lijuan Wang, Yejin Choi and Manling Li. 2025. RAGEN: Understanding Self-Evolution in LLM Agents via Multi-Turn Reinforcement Learning. arXiv:2504.20073.
@misc{wang2025ragen,
title = {{RAGEN: Understanding Self-Evolution in LLM Agents via Multi-Turn Reinforcement Learning}},
author = {Zihan Wang, Kangrui Wang, Qineng Wang, Pingyue Zhang, Linjie Li, Zhengyuan Yang, Xing Jin, Kefan Yu, Minh Nhat Nguyen, Licheng Liu, Eli Gottlieb, Yiping Lu, Kyunghyun Cho, Jiajun Wu, Li Fei-Fei, Lijuan Wang, Yejin Choi and Manling Li},
year = {2025},
doi = {10.48550/arxiv.2504.20073},
eprint = {2504.20073},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2504.20073}
}References
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