Switching orgs at Microsoft: do you have to do a full interview loop again?

Yes, usually a full loop, four or five interviews like an external candidate. Your current manager technically doesn't have to approve it, but if they don't, the new team will notice. The real blocker is headcount: no open req, no transfer. Best time to move is right after a reorg. Budget 3 to 6 months from first chat to start date.