Researchers writing in Nature present MIRA, an autonomous medical AI agent that works inside a sandboxed electronic health record, ordering labs and imaging, forming diagnoses, prescribing, and planning admissions under FHIR and major coding systems. On more than 500 MIMIC-IV emergency cases spanning surgery, internal medicine, and oncology, it reached about 88% diagnostic accuracy and matched or exceeded board-certified physicians on a matched subset, with strong medication-safety checks. Why it matters: the bar is moving from chat advice to governed clinical actions. Caveat: results are simulation-based on retrospective notes, so prospective hospital trials are still required.