Late-2013 iMac 4k@60Hz

[Bullzie]

I would like to know if anyone has been able to make this work and if so how did you go about doing it? It is very frustrating because if I Bootcamp into Windows 10 it works just fine at 4k60Hz without even doing anything. Whatever I try with MacOS never gets me past 30Hz.

 

[294307]

I don't quite follow what your problem is. Are you trying to connect an external monitor to your iMac that supports 4K? If that's the case, the Late 2013 iMac only supports external resolutions up to 2560 by 1600 at 60 Hz. Technically, 4K is 4096 x 2160, but many monitors at 3840 x 2160 are being promoted as 4K these days.

If you could clarify what you are actually trying to do, we might be able to help you further.

Edit: Late 2013 iMacs only supports up to 2560 x 1600, not 3840 x 2160 as originally thought.

 

[Bullzie]

My apologies, now that I re-read what I posted I did leave out a lot of details. First off, I have already gotten a 4k monitor hooked up and I should clarify that when I say 4k in my situation that is 3840x2160. My issue is getting it to run at 60Hz. I have tried numerous 'active' adapters to get to 60Hz but the best I have been able to get is 4k30Hz. I am running 10.13.6. Where it gets frustrating is that when I Bootcamp into Windows 10, without changing anything (cable, HDMI/mDP, adapter, etc) it automatically runs fine in 60Hz. So my issue isn't a hardware problem, there is some software issue in MacOS that is holding me back. This is my 'needle in a haystack' as whatever utility I have tried I just can't seem to get it running at 60Hz.

 

[294307]

After looking into this further it appears that the Late 2013 27-inch iMac only supports resolutions up to 2560 x 1600, according to Apple's technical specifications for your iMac (and I presume it is a 27-inch model you have). It's very likely that macOS is refusing to enable resolutions higher than this, and even so, Windows 10 might be running the monitor at below 60 Hz but higher than 30 Hz to fit within the bandwidth constraints of first-gen Thunderbolt, given that you have witnessed the machine actually supporting 3840 x 2160. As far as I know, Thunderbolt 1 does not support 4K @ 60Hz (but may do at lower frequencies such as 50 Hz).

I should also point out that some monitors only support their native HiDPI resolution on specific ports. I have purchased monitors in the past with both DisplayPort and HDMI ports on them, with only the DisplayPort supporting the necessary bandwidth to drive 4K @ 60 Hz.

Sorry I don't have a solution for you. It might simply not be possible. A last-ditch attempt would be to try SwitchResX and to try 3840 x 2160 at a lower frequency such as 50 Hz. There are instructions on how you can create custom resolutions in the first FAQ item here.