When they get that big, you usually have engineering support. Standard breaker sizes in article 240 are 1600 2000 2500 3000 4000
5000 6000 but there are bigger ones. I suppose you could dig out all the answers you need from the NEC but I have always been looking at engineered drawings when I see anything much over 800 amps. It was only a few times inspecting but in computer center design, 1600a or 2000a services were not unusual before computers got small.
