The 75 mph (120 km/h) locomotive has a maximum tractive effort of "up to" 500 kN (110,000 lbf), and a power rating of 6,170 kW (8,270 hp) in electric mode.

[2] These figures exceed those of the diesel-powered British Rail Class 66.

The Class 99 locomotive has a 16-cylinder 1,790 kW (2,400 hp) Cummins QSK50 engine installed.

[2] Peter Dearman, an expert in traction electrification,[3] reported in Rail Engineer in early 2023 that the Class 99 may only be able to deliver 1,600 kW (2,100 hp) at the rail in diesel mode.

[8][9] The locomotive was formally launched by GBRf in September 2024 at Innotrans 2024.