The inbred and some other On One frames used to come with changeable dropouts (swapouts) a few years ago, then, they changed to just doing 3 versions of the frame, one with vertical (geared dropouts), one with sliding dropouts and a gear hanger, and one just with sliding, horizontal dropouts for single speed use.
It seems they haven’t got the sliding dropout with hanger version anymore. You could just go for vertical and use a tensione/conversion kit on a cassette hub if you think you might want gears, all depends how much ss’ing or geared riding you’ll do, as the conversion will be a compromise compared to a proper ss frame.