New Features

• Add support for bucket retention policies (#5534)
• Allow destination.content_type to be None in Blob.compose. (#6031)

Implementation Changes

• Ensure that method for Blob.generate_signed_url is uppercase. (#6110)

Documentation

• Clarify GCS URL signing limitations on GCE (#6104)
• Redirect renamed 'usage.html'/'client.html' -> 'index.html'. (#5996)