Can a Bucket and Its Objects Use Different Storage Classes?

Yes.

By default, an object inherits the storage class of its bucket when it is uploaded. However, you can specify a different storage class for the object during upload, and you can also change the object's storage class after the upload is complete.

Changing the storage class of a bucket does not change the storage class of existing objects in the bucket. However, any new objects uploaded to the bucket will inherit the bucket's new storage class.