The new version of the Oak Segment Tar present since AEM 6.3 requires a repository migration. This step is mandatory if you are upgrading from an older version of TarMK or want to switch the new Segment Tar from another type of persistence. For more information on what the benefits of the new Segment Tar are, see the Migrating to Oak Segment Tar FAQ.
Various enhancements have been made to the UI to make it more productive and easier to use.
Adobe will not make further enhancements to the Classic UI. Experience Manager 6.5 includes Classic UI for backward compatibility. Classic UI remains fully supported while being deprecated Read more.