A company stores millions of ringtone files (each at least 128 KB) in Amazon S3 Standard. Downloads are infrequent for ringtones older than 90 days. The company wants to reduce storage costs while keeping frequently accessed files readily available. Which action is the MOST cost-effective?

The most cost-effective solution is to implement an S3 Lifecycle policy that moves objects from S3 Standard to S3 Standard-Infrequent Access (S3 Standard-IA) after 90 days. This directly addresses the requirement to reduce costs for infrequently accessed files while keeping them readily available. S3 Standard-IA is designed for data that is accessed less frequently but requires rapid access when needed. Configuring S3 Standard-IA as the initial storage tier is incorrect because new ringtones are frequently accessed, making S3 Standard more appropriate for the first 90 days. Moving files to S3 Intelligent-Tiering is an option, but an S3 Lifecycle policy to S3 Standard-IA is more cost-effective here because the access pattern is predictable (infrequent after 90 days), eliminating the overhead of Intelligent-Tiering's monitoring and auto-tiering. Configuring S3 inventory to manage objects is not a storage class itself; it's a tool for managing objects, not for automatically changing their storage class to reduce costs.