The OS X Mavericks 10.9.3 Update is recommended for all Mavericks users. It improves the stability, compatibility, and security of your Mac.10.9.3 will include improved 4K display support, enabling a HiDPI "Retina" scaling option for 4K monitors used with the 2013 Mac Pro and the 2013 Retina MacBook Pro, along with a 60Hz refresh rate.
- 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
For detailed information about this update, please visit: http://support.apple.com/kb/HT6228
For detailed information about the security content of this update, please visit: http://support.apple.com/kb/HT1222
It is unclear exactly when the beta might be released, but it could be as soon as this afternoon.