An Experimental Paradigm for Evaluating Shared Agency in Humans and LLMs

Coordination is central to social life, yet LLMs are poor coordinators. We introduce the Hangman game as a novel experimental paradigm to study why. Our focus is on shared agency, a precondition for coordination, defined as the ability to form shared goals, intentions, and plans. Success in Hangman requires agents to coordinate on word choices across rounds. Human teams reliably develop shared strategies, coordinating on mutually predictable word patterns. LLMs fail to do so. Across Human-Human, Human-LLM, and LLM-LLM teams, humans outperform all tested state-of-the-art LLMs, and humans paired with LLMs perform worse than when paired with other humans. As LLMs are increasingly deployed as collaborative agents, coordination failures undermine their usefulness. Hangman offers a flexible, controlled method for measuring and tracking coordination skills as models develop.