Which feature is configured to define when objects are moved to another storage class in S3?

Transition actions are the feature in Amazon S3 that defines when objects are moved to another storage class. This is part of the S3 Lifecycle Management capabilities, which allow users to automate the process of moving data between different storage classes based on specified rules. Transition actions can be set based on the age of the objects or specific dates, enabling cost optimization by moving infrequently accessed data to lower-cost storage classes such as S3 Standard-IA (Infrequent Access) or S3 Glacier over time.

In contrast, expiration actions are used to automatically delete objects after a specified period but do not govern the movement to a different storage class. Availability zones and bucket regions relate to the geographical and availability structure of AWS infrastructure but do not pertain to the management of object lifecycle in terms of storage class transitions. Thus, the ability to specifically determine when objects transition to a different storage class through defined rules clearly identifies transition actions as the correct feature in this context.