3 FOs upgraded into the jet but they are all senior. Most junior one of those three is 3+ year seniority. There's about 10 jet captains who are very junior (1.3-1.5 years seniority) who were able to get it during an opportunistic time window. They will be reserve for the rest of their careers at horizon though.
Upgrade/transition is the same thing for the jet. There's no restrictions, if your seniority can hold it you will get it if you're not seatlocked.