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arXiv · 2609.31590

AgentWorld: Benchmarking Long-Horizon Collaboration of Multi-agent LLMs

Raphael Shu·Yusen Zhang·Young Min Cho·Jin Mo Yang·Yuan Yuan·Wenliang Zheng·Sharath Chandra Guntuku·Lyle Ungar·Zhou Yu·Rui Zhang
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Abstract

Existing multi-agent benchmarks primarily test in competitive settings, short-horizon interactions under 20 steps, or simply aggregate individual performance, failing to isolate and highlight genuine collaboration capabilities of LLM-based agents. We introduce AgentWorld, a benchmark of 100 human-annotated tasks (with 100 augmented variants) for evaluating long-horizon, multi-agent collaboration. Tasks span 50+ interaction rounds across a rich MMORPG sandbox and require 3-20 agents with asymmetric roles and abilities to coordinate through communication, joint planning, and resource sharing under a blackbox setting where each agent acts independently without access to others' internal states. To quantify collaboration effectiveness in addition to conventional binary task success, we propose Causal Collaboration Effectiveness (CCE), a graph-based metric that traces causal dependencies between agent actions and measures what fraction of a team's effort actually contributed to the outcome. Experiments with Gemini 3 Flash, Claude Haiku 4.5, GPT-5 Mini, and DeepSeek R1-70B show that even the best model achieves only 52.0% task success, with systematic failure modes including communication breakdowns, role confusion, and inability to maintain shared plans across rounds. AgentWorld is fully open-source.

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Raphael Shu, Yusen Zhang, Young Min Cho, Jin Mo Yang, Yuan Yuan, Wenliang Zheng, Sharath Chandra Guntuku, Lyle Ungar, Zhou Yu, Rui Zhang. 2026-09-25. AgentWorld: Benchmarking Long-Horizon Collaboration of Multi-agent LLMs. https://arxiv.org/abs/2609.31590

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