This update is recommended for all Mac Pro (Late 2013) systems. It includes all updates from OS X Mavericks 10.9.1 plus system-specific enhancements and fixes to improve the stability and compatibility of your Mac.
This update includes the following fixes:
Improved support for Gmail in OS X Mail, and fixes for users with custom Gmail settings
Improves the reliability of Smart Mailboxes and search in Mail
Fixes an issue that prevented contact groups from working properly in Mail
Resolves an issue that prevented VoiceOver from speaking sentences that contain emoji
Updates Shared Links periodically when open in the Safari Sidebar
For detailed information about this update, see About the OS X Mavericks 10.9.1 Update