Colosseum paper finds most off-the-shelf LLM agents prone to collusion
nandofioretto · x · 2026-09-28
A new arXiv paper from UMass Amherst and collaborators introduces Colosseum, a framework for auditing collusive behavior among LLM agents in cooperative multi-agent systems. Key findings:
- Grounds collusion measurement in a formal multi-agent decision-making framework, comparing action-based collusion (regret vs. the cooperative optimum) with communication-based collusion.
- Supports audits across benign settings, different coalition objectives, persuasion tactics and network topologies.
- A new behavioral probe creates secret communication channels between agents: most out-of-the-box models show a propensity to collude under this probe, termed emergent collusion.
- The paper also documents "collusion on paper" — agents plan to collude in text but often choose non-collusive actions in practice.
Related event: Colosseum paper shows LLM agents prone to collusion(4 posts)→
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