cs.AIMar 5, 2026

STRUCTUREDAGENT: Planning with AND/OR Trees for Long-Horizon Web Tasks

Authors: ELita Lobo, Xu Chen, Jingjing Meng, Nan Xi, Yang Jiao, Chirag Agarwal, Yair Zick, Yan Gao

Organizations: University of Massachusetts Amherst · Amazon · Virginia Commonwealth University · University of Virginia

Abstract

Existing LLM-based web agents struggle on complex, long-horizon tasks due to limited in-context memory, weak planning abilities, and greedy behaviors that lead to premature termination. To address these challenges, we propose \SA{}, a hierarchical planning framework that interleaves planning and execution via dynamic \ANDOR\ANDOR trees. The framework separates structural planning from LLM-based reasoning, enabling principled error recovery through node repair, systematic exploration of alternatives via OR nodes, and modular plans that can facilitate human intervention. On WebArena (630 tasks), \SA{} achieves a ∼\sim53% success rate vs.\ ∼\sim46% for AgentOccam, and on complex multi-constraint Amazon shopping tasks, gains reach 10% over the strongest baseline.

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