MBP (2015) supports 4k monitor in yosemite but not in bootcamp Win 8.1

[Akbermo]

I've got a dell p2715q 4k monitor that I connect to MBP (mdp to dp). It works at 4k in Yosemite @ 60Hz, but maxes out at 1440 in bootcamp windows 8.1. I can use a hdmi on windows at 4k 30Hz but I can't get the display port 4k 60hz to work on windows. Any ideas?

I have updated iris drivers .

 

[tezagt]

Did you ever find a fix to this? I have the same issue.

Using a P2715Q, a 2015 13" rMBP, mDP to DP cable, and I can't get Windows 8.1 in Bootcamp to work 3840x2160 @ 60 Hz, it only allows 29 Hz or 30 Hz. Booting into OS X gives me 3840x2160 @ 60 Hz just fine.