The ABB XT1SU3050AYD000XXX is a molded case circuit breaker from the NEXT1S 125 series, a 3-pole unit with a TMF 50-500 A trip unit, marked for UL/CSA compliance. That's another SKU that sits in the standard MCCB footprint — no special mounting or oddball cutout to worry about when swapping into an existing panel.
The description decodes as NEXT1S 125 frame, TMF (thermal-magnetic fixed) trip unit rated 50-500 A, 3-pole, with front terminals and UL/CSA certification. The TMF trip gives you a fixed thermal and magnetic pickup — no field-adjustable dials, so the trip curve is set at the factory. For a panel builder, that means one less thing to verify during commissioning, but the trip rating must match the load calcs exactly at order time.