• Renamed message types
• pyout vs display_data
• display metadata
• Python API changes
• Notebook format changes
• Third-party use of metadata
• Application: image shapes
• Backward compatibility
• multiple objects
• getpass
• Message headers
• kernel_info
• mime-bundles
• object_info_reply
• JSON data
• user_expressions / user_variables
• Payloads
• pager mime-bundle