Most likely, the Upper Bus Kit will be rated for 400 Amps Continuous (400 Amps drawn for >180 Minutes), as the Service Disconnect is rated 400 Amps. The (2) 200 Amp 2 Pole Devices may draw 200 Amps each, and continue to draw 200 Amps steadily until the Sun Supernovas; yet will not trip.
A Residence drawing 400 Amps continuously is unlikely, so the KWH Meter and Meter Socket might be rated as 400 Amp Maximum, 320 Amps Continuous. The KWH Meter should indicate this on the front label, as: "CLASS 320". (BTW, "KWH" = KiloWatt-Hour; referring to the Utility's Revenue Meter).
Fault Bracing for the Upper Bus Kit is likely to be 22KA, but could be as high as 30KA or even 42KA.
The highest Rating which the Lower Bus Kit would be rated for is 225 Amps Continuous (225 Amps for >180 Minutes). The Lower Bus Kit should be Nominally rated as 200 Amps Continuous (200 Amps for >180 Minutes).
The Bus Tabs (Plug-In stabs for the Over Current Protection Devices), will typically be rated 100 Amps Max., 70 Amps Continuous.
Fault Bracing for the Lower Bus Kit would mimic the Upper Bus Kit: 22KA Nominal; 30KA or 42KA optional.