Minimum version : 9.20.
Recommended version : 9.51.
Last available version : 9.51.
QuarkXPress version 9 was tested extensively by both Xtensions developers and the general public, before its release and has seemed to be free of any show-stopping defects from day 1, just as Quark 8 was.
However, in late 2011 the file format and internals of QuarkXPress 9.1 was changed with the result that the minimal version of QuarkXPress 9 is 9.20.
See also: other QuarkXPress versions.