Gimp still lacks full CMYK color model support. The ability to separate and then edit an image in CMYK mode is still a long way down the list of features to be added. … separate a RGB image. color management (using ICC profiles and lcms)

Does Gimp use RGB or CMYK?

edit: Just a thought: Do not open the CMYK in Gimp for other than viewing. Edit or re-export and Gimp uses RGB colourspace.

Can gimp open CMYK files?

As you found Gimp does not support cyan-magenta-yellow-black (cmyk) colour space. Gimp is a red-green-blue (RGB) bitmap editor.