Quote Originally Posted by KDSilver View Post
9S is not a guaranteed drop.
Per the patch notes, 9S and other items like the Stuffed Android Units "will now appear in a treasure chest allotted to each party of an alliance when undertaking the Tower at Paradigm's Breach" meaning the intent was to have all of the drops be 100% for each party akin to what was done with the previous two alliance raids and their rare drops in 5.5.