The interrupting ratings tell the real story: 187 kA at 240 V AC, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, and 7.5 kA at 690 V. That 187 kA figure at 240 V gives you serious SCCR headroom for high-fault panels; the drop to 7.5 kA at 690 V is the limit to watch if you're feeding a 690 V bus. The thermal-magnetic trip unit is fixed at 400 A; the minimum adjustable trip is 600 A, maximum 4 000 A, so this is a fixed-trip frame, not an electronic-trip with a wide adjustment band.
At 40, 45, and 50 °C ambient the breaker holds full 400 A. Above that it derates linearly: 385 A at 55 °C, 370 A at 60 °C, 355 A at 65 °C, 340 A at 70 °C. If your panel ambient runs 55 °C — common in a cement plant control room or a packed MCC lineup — you lose 15 A. Plan your load accordingly; don't size the breaker at 400 A for a 400 A load if the enclosure runs hot.