With your built-in HDMI port you can use 4K displays at the following resolutions and refresh rates:
● 3840 x 2160 at 30 Hz refresh rate
● 4096 x 2160 at 24 Hz refresh rate (mirroring is not supported at this resolution)
With OS X Mavericks v10.9.3 or later, the following DisplayPort displays are supported at their default 30 Hz using single-stream transport (SST).
● Sharp PN-K321
● ASUS PQ321Q
● Dell UP2414Q
● Dell UP3214Q
● Panasonic TC-L65WT600
MacBook Pro (Retina, Late 2013) or Mac Pro (Late 2013) also support 60 Hz displays using multi-stream transport (MST). These displays need to be manually configured to use MST. Follow the steps below to use the display's built-in controls to enable this feature.
● Sharp PN-K321: Choose Menu > Setup > DisplayPort STREAM > MST > SET
● ASUS PQ321Q: Choose OSD menu > Setup > DisplayPort Stream
● Dell UP2414Q and UP3214Q: Choose Menu > Display Setting > DisplayPort 1.2 > Enable
● Panasonic TC-L65WT600: Choose Menu > Display Port Settings > Steam Setting > Auto
Your Mac will automatically detect an MST-enabled display. However, your display may require a firmware update to support 60Hz operation.
Adjusting your display
Use System Preferences > Displays to adjust or scale the resolution on your display. This can make text and objects appear larger or give you more space on your screen.
Hovering your mouse over one of the resolution options will show more detail on that option. To get a Detect Displays button to appear, press the Option key. To see all the available resolutions, hold down the Option key while clicking the Scaled button.
More details in the full support document linked below...
Read More [via Emad]