Large SE wires, what's the rating?

I’ve never run across this gauge wire on a main panel, does anyone know what kind of service I’m looking at? The panel reads 400 Amps max, but that doesn’t tell me what’s actually there. There isn’t a main disconnect, instead there’s the six breakers. These are the largest SE wires I’ve run across to date. Any input would be appreciated!!


After 4/0, you go into kcmils. 400amp service would need 400kcmil CU or 600kcmil AL size wire.