Here in NJ (Northern) a RESI 400 amp can be thru a meter pan. (320 continuous, single phase) or a CT can be installed. PSE&G territory. 3 phase is 200 amp meter pan, larger is CT.
Occasionally, a CT cab is omitted, and donut CT's placed on a rack at the weatherhead. Note 'occasionally'!
IMHO, the POCO is the 'boss', so you don't have much choice.