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M4Bench gave clinical AI agents 28 EHR derivation tasks, and found the specification mattered more than the agent skills everyone was shipping

AspireAI community · arXiv
*Clinical research over electronic health records depends on derived variables whose definitions live outside the schema - item codes, time windows, missingness rules - and the M4Bench finding is that writing those rules down beats anything you hand the agent.* The benchmark spans 28 derivation tasks across 15 task families on MIMIC-IV and eICU, with controls that separate the value of agent skills into specification completeness, delivery format and schema familiarity. In a Docker-isolated Codex campaign with GPT 5.4 Mini and GPT 5.5, clinician-reviewed skills raise reward by 0.136 with 26 of 28 tasks improving - but on an eight-task control subset an operational specification alone raises reward by 0.162, and the skills add only 0.024 on top of that, which is indistinguishable from zero. The honest headline is the second number: only 25 of 280 with-skill and 13 of 280 no-skill Codex runs pass every strict check, and skills barely change which rows come back (key F1 +0.003). A Claude Code replication across 560 runs is directionally consistent (+0.120, 21 of 28 improving). The benchmark, skills and sanitized per-run evidence are released.
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