Well Spartan's post war have their own branch in the UNSC military called the Spartan Branch, former 2's 3's and current 4's dont have their ranks anymore and just go by Spartan (name whatever) the only ones that have a rank/title is Sarah Palmer as Spartan Commander which is the highest and they run all ops on whatever ship/military installation Spartans are stationed on.

[url=https://halo.fandom.com/wiki/Spartan_(Branch)]Source from wiki[/url]