Training AI agents using Reinforcement Learning (RL) to handle complex, multi-turn tasks is notoriously difficult.Traditional methods face two major hurdles: high computational costs (generating numerous interaction scenarios, or "rollouts," is expensive) and sparse supervision (rewards are only given at the very end of a task, making it hard for the agent to learn which specific steps were useful).

In this episode, we explore "Tree Search for LLM Agent Reinforcement Learning," by researchers from Xiamen University, AMAP (Alibaba Group), and the Southern University of Science and Technology. They introduce a novel approach called Tree-GRPO (Tree-based Group Relative Policy Optimization) that fundamentally changes how agents explore possibilities.

Tree-GRPO replaces inefficient "chain-based" sampling with a tree-search strategy. By allowing different trajectories to share common prefixes (the initial steps of an interaction), the method significantly increases the number of scenarios explored within the same budget. Crucially, the tree structure allows the system to derive step-by-step "process supervision signals," even when only the final outcome reward is available. The results demonstrate superior performance over traditional methods, with some models achieving better results using only a quarter of the training budget.

📄 Paper: Tree Search for LLM Agent Reinforcement Learning https://arxiv.org/abs/2509.21240