8/9-speed HG freehubs take 10-speed HG cassettes, in most cases with a 1mm spacer because of the undercut on 10-speed cassettes with spider-mounted big sprockets. I thought the 11-speed MTB cassettes were supposed to have an even bigger undercut to allow them to fit on 8/9/10-speed hubs too.
8/9-speed HG freehubs take 10-speed HG cassettes, in most cases with a 1mm spacer because of the undercut on 10-speed cassettes with spider-mounted big sprockets. I thought the 11-speed MTB cassettes were supposed to have an even bigger undercut to allow them to fit on 8/9/10-speed hubs too.