The One:1 name comes from the power (1361 PS) to weight (1361 kg) ratio and the fact that this is the first production car to produce a megawat of power.
Koenigsegg says this is a more focused as a track car than the previous cars it has produced. From the photos, I have to agree. This Koenigsegg One:1 definitely looks more aggressive and racey.
Koenigsegg had to sacrifice a few things to be able to achieve their goal with the car. There is an airscoop on the removable roof, so it would not have been possible to stow the roof in the trunk like previous models. As such, Koenigsegg have taken advantage of this and modeled the front to create more downforce, which reduces trunk capacity by 40%.
Powerplant-wise, the Koenigsegg One:1 has a variant of the same 5.0-litre twin-turbocharged V8 engine used in the Koenigsegg Agera. It produces 1,361 PS (1,001 kW) at 7500 rpm and 1,371 N·m (1,011 lb·ft) of torque at 6000 rpm. Total weight of the engine is only 197 kg (434 lb) thanks to a carbon fiber intake manifold and the aluminium construction. The transmission is a 7-speed dual clutch paddle shift.