Hi
I am curious about 400 amp service. Some one told me that it is actually split into two 200 amp panels. Where dot hey split it at and do they treat one panel like a subpanel. What should I be looking for
Thanks
J

A residential 400A service is typically 400A total and 320A continuous. This is why many times you'll see it listed as a 320A.

The easiest and best way to do this is with two 200A panels. One 400A panel will only give you the same 40-42 panel spaces, only with more amperage capacity. You STILL need sub-panels.
A two 200A setup will most times give you all the breaker space you need, is cheaper, easier to install, and takes up less room.

Usually they are split at the meter. A single larger lateral or service drop on the line side, and parallel 200A service entrances on the load side.

When you say "What should <you> be looking for", what do you mean? Where are you looking?