Hi Kevin,
I am not with Laminar Research; just a flight simmer.
The last version of X-Plane 10 was version 10.26. This was completed just after the initial release of XP11.
From then on all development has been on version XP11 and continues to this current day. Earlier in this forum others like yourself asked the same question and Laminar Research advised that any development work on XP10 had ceased.
Good luck
Glenn