What feature allows S3 bucket owners to shift data transfer costs to the requester?

The feature that allows S3 bucket owners to shift data transfer costs to the requester is known as "Requester Pays." When this feature is enabled on an S3 bucket, the requester (who is accessing or retrieving the data) becomes responsible for the data transfer costs rather than the bucket owner. This is particularly useful for use cases where large datasets are shared with multiple users, such as in research or public datasets, where the bucket owner may not want to bear the costs of data transfer for every user accessing the data.

By configuring the "Requester Pays" option, the bucket owner can maintain control over cost management and can effectively handle situations where many requests come from users who might not necessarily be contributing to the operational costs of storing the data. Requesters will need to ensure their AWS account is set up to handle these costs if they wish to access the data, which encourages responsible usage.

The other options, while they offer various functionalities within Amazon S3, do not pertain to the shifting of data transfer costs. S3 Batch Operations allows for bulk processing of S3 objects, S3 Event Notifications enable triggering workflows based on bucket events, and S3 Default Encryption ensures that all new objects in a bucket are automatically encrypted. None of these features involve altering