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A frontier MLLM driving a robot beats post-trained policies on short tasks, and loses on long ones

AspireAI community · arXiv
EBench measures GPT-6 Astra controlling a robot through an agent harness under the same visual and proprioceptive protocol as post-trained vision-language-action and world action model policies. On direct control the agent leads on short-horizon tasks and shows the least performance variation across generalization dimensions, but underperforms post-trained policies on long-horizon tasks, tabletop manipulation and high-precision contact-rich work. Giving the agent the option to hand execution to a post-trained policy lifts overall task success to the level of the strongest compared policy while cutting token cost, yet the combined system still sits below the per-task ceiling of its own components because of suboptimal policy invocation and grasp disruption when control resumes. The paper positions this as a characterization of the capability boundary of a frontier agent rather than a recipe for winning, and the evaluations cover a fixed set of manipulation tasks rather than general robot work.
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