macOS Sierra doesn't scale for 4k monitor

I just upgraded to macOS Sierra. In El Capitan, I could have my 4k monitor (Dell P2715Q) scale so it was the equivalent of a 2560x1440 monitor, but in Sierra it only lets me do 2k/4k resolutions now.

Anyone know of a fix?

Solution 1:

Immediately I thought to recommend enabling HiDPI mode, which basically allows you to change the display to use half of the real pixel density without changing the resolution:

sudo defaults write /Library/Preferences/com.apple.windowserver.plist DisplayResolutionEnabled -bool true

but then I did the math and realized that you want 2/3 of your full resolution, not half.

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^ This feature does not seem to be applicable in macOS Sierra anymore.

Third party apps such as 'QuickRes' and 'SwitchResX' don't resolve the issue. They only see the same resolutions that macOS sees.

For what it's worth, a reboot should fix it temporarily when you have your display plugged into your laptop. Once the screen sleeps though the issue returns.