S3 Glacier Flexible Retrieval is designed for long-lived archive data that is accessed infrequently and can be retrieved in minutes to hours, making it a strong cost-effective choice for medical records that are rarely accessed. AWS documentation states that standard retrievals from this storage class typically finish in 3 to 5 hours, which fits the requirement to retrieve records within a few hours. For immutability, AWS S3 Object Lock provides a WORM model and can prevent deletion or overwriting for a fixed retention period. Together, Glacier Flexible Retrieval and Object Lock satisfy the needs for low-cost archival storage, long retention, immutability, and acceptable restore times. S3 Standard and Intelligent-Tiering cost more than necessary for rarely accessed 10-year data, and One Zone-IA does not provide the same resilience posture.

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