How does Bloomberg promotion from junior to senior work?

It's based on tenure but it's pretty non-eventful. The title change only shows up in some internal platforms that people don't check on their day to day, and the performance review of the year you get promoted is not noticeably better than that of other years. As a matter of fact, having made it to senior only randomly came up in conversations with my manager a year or a couple years after it happened.

usually 3 years

You asked for it in your 1 on 1, then you full out this eval sheet on why you're senior material. Just put the usual bullsht on it. Then the TL give you a couple trial sprints. Offer you less help than usual and scope out less detail ticket, etc. after that you get promoted. Can be done in a few weeks if you already doing senior level work.

It’s not a promotion, it’s a label. You get hired as an N year junior and when N=4… boom senior. If you look at your role on the HR portal the day of your anniversary it will update and not the day before. Your eval ranking is relative to other N years and once you are senior the pool is all seniors.