Seems that you can get the black models for a extra $25 more here.
https://www.glockstore.com/Glock-43X-9mm?quantity=1&color=1&custcol9=93
https://www.glockstore.com/Glock-48-9mm?quantity=1&color=1&custcol9=93
Just called glockstore. They are stripping the slides and “refinishing with black oxide” They’re not coming from Glock with black slides.