EnactToM: An Evolving Benchmark for Functional Theory of Mind in Embodied Agents

Theory of Mind (ToM), the ability to track others' epistemic state, makes humans efficient collaborators. AI agents need the same capacity in multi-agent settings, yet existing benchmarks mostly test literal ToM by asking direct belief questions. The ability to act optimally on implicit beliefs in embodied environments, called functional ToM, remains largely untested. We introduce EnactToM, an evolving benchmark of 300 embodied multi-agent tasks set in a 3D household with partial observability, private information, and constrained communication. Each task is formally verified for solvability and required epistemic depth, and new tasks are generated to increase difficulty as models improve. On the hard split, all seven evaluated frontier models score $0.0\%\,\mathrm{Pass}^3$ on functional task completion, while averaging $45.0\%$ on literal belief probes. Manual analysis traces $93\%$ of sampled failures to epistemic coordination breakdowns such as withheld information, ignored partner constraints, and misallocated messages, providing a concrete target for future work.