Mercedes-AMG continues to fine-tune the all-new GT 4, subsequent to its Geneva Motor Show presentation in March.

The latest spy video comes from YouTube channel AutomotiveMike and shows several pre-production models being driven on the Nurburgring.

The Affalterbach-born four-door coupe with supercar performance, which serves as a more upscale replacement for the old AMG CLS 63, will arrive at dealers across Europe later this year. Subsequently, it will launch in the United States early next year, with the ’53’ model following from mid-2019.

Mercedes-AMG has already detailed the Edition 1 earlier this week, which features a few updates, such as special exterior amenities and the AMG Aerodynamics Package.

Opening the door reveals the illuminated AMG door sills, exclusive leather upholstery with contrast stitching, yellow seatbelts, special floor mats and other gizmos. The AMG GT 4 special edition welcomes the Air-Balance Package, too, along with the Multicontour Performance Seats with Memory Package and matte carbon fiber trim.

Powering it is the twin-turbo 4.0-liter V8 engine, which pushes out 639PS (630hp / 470kW) and 900Nm (664lb-ft) of torque. The mill is married to a nine-speed automatic transmission, and the all-wheel drive GT 63 goes from rest to 100km/h (0-62mph) in 3.2 seconds. Top speed is 315km/h (196mph).

Mercedes-AMG might eventually equip the GT 4 with a hybridized powertrain. Previewed in the AMG GT Concept last year, it combines the V8 lump with an electric motor, and could produce as much as 800hp, as the performance brand’s head honcho Tobias Moers recently confirmed in an interview.