The OS X Mavericks 10.9.3 Update is recommended for all Mavericks users. It improves the stability, compatibility,m and security of your Mac.
● Improves 4K display support on Mac Pro (Late 2013) and MacBook Pro with 15-inch Retina Display (Late 2013).
● Adds the ability to sync contacts and calendars between a Mac and iOS device using a USB connection.
● Improves the reliability of VPN connections using IPsec
● Includes Safari 7.0.3
Apple is expected to release OS X 10.9.3 to the public soon as it is already testing 10.9.4.