The ABB GHS2901909R0011 is a shunt trip accessory for circuit breakers, used to remotely trip the breaker via a control signal. It sits in the circuit breaker accessory category, subcategory trip devices, so it's the piece that receives a voltage signal and mechanically releases the breaker latch. That's another SKU I don't need to second-guess — the part number is right on the box.
No obsolescence notice or successor part number appears on record.
Mounts inside the breaker panel, wired to a control voltage source. The shunt trip coil draws current only during the trip pulse.