Apple has updated a support document on its website to reflect that the high-end 15-inch Retina MacBook Pro, equipped with AMD Radeon R9 M370X graphics, is capable of driving Dell's dual-cable UP2715K 27-inch 5K display



From MacRumors:

Apple initially released OS X 10.10.3 in April with support for the dual-cable 5K monitor on the Retina 5K iMac and 2013 Mac Pro, but no notebooks supported the display at the time.Dual-Cable Displays Some displays with resolutions higher than 4K require two DisplayPort cables to connect the display at full resolution. With OS X Yosemite v10.10.3 or later, the Dell UP2715K 27-inch 5K display is supported on the following Mac computers: Mac Pro (Late 2013) iMac (Retina 5K, 27-inch, Late 2014 and later) MacBook Pro (Retina, 15-inch, Mid 2015) with AMD Radeon R9 M370XDell's dual-cable 5K display requires more bandwidth than is currently supported over a current single DisplayPort cable, so it uses a dual-cable solution that takes up two Thunderbolt ports on a Mac.

  Apple Adds High-End 15" Retina MacBook Pro to List of Macs Supporting Dell's 5K Display