Well, documentation I have read seems to indicate everything should work in 2.1 if it works in 2.0 however, simply changing the api version to 2.1 on a existing client script gives the message "Failed to validate script type: unsupported script type ClientScript ...". I have tried the same upload with a User Event Script and it seems to work. I am running Eclipse Mars 2, release 4.5.2 and have already applied the latest updates, so I tend to think that is not the problem.