A company stores backup files in Amazon S3 Standard. Files are accessed frequently for the first month, then not accessed afterward. The company must retain the files indefinitely. Which storage solution is MOST cost-effective?

The most cost-effective solution is to transition objects to S3 Glacier Deep Archive. The problem states files are accessed frequently for the first month and then not accessed afterward, but must be retained indefinitely. S3 Glacier Deep Archive is the lowest-cost storage class for long-term archival and is suitable for data that is rarely accessed. An S3 Lifecycle rule automates this transition. Transitioning to S3 Intelligent-Tiering is less cost-effective because while it automatically moves objects, S3 Glacier Deep Archive offers lower storage costs for indefinite retention of rarely accessed data. Transitioning to S3 Standard-Infrequent Access (S3 Standard-IA) or S3 One Zone-Infrequent Access (S3 One Zone-IA) is not as cost-effective as S3 Glacier Deep Archive for data that is rarely accessed and needs indefinite retention, as S3 Glacier Deep Archive has significantly lower storage costs.