The Mercedes-AMG GT 4-Door Coupe first made its debut at the 2018 Geneva Motor Show and is currently being offered in four variants, including the GT 43 4Matic+, GT 53 4Matic+, GT 63 4Matic+ and GT 63 S 4Matic+. A fifth addition to the line-up will be the GT 73 EQ Power+, which was first teased at the tail end of 2019, and has now been captured by our spy photographers.

The GT 73 will be the plug-in hybrid version of the AMG super sedan, and is rumoured to be powered by a 4.0 litre twin-turbo V8 with an electric motor that draws power from a lithium-ion battery. This setup is said to provide a total output of 800 hp (812 PS) and a zero to 96 km/h (0-60 mph) time of under three seconds. If all this sounds vaguely familiar, look back to the GT Concept that first previewed the GT 4-Door Coupe in 2017.

Compared to the current GT 63 S that has 630 hp (639 PS) and 900 Nm of torque on tap from its V8, the GT 73 looks to have a clear advantage in terms of horsepower thanks to the addition of an electric motor. Aside from improved performance, expect the GT 73 to offer better efficiency and fuel economy as well.

Based on the photos provided, the test vehicle doesn’t look too different from a regular GT 63/63 S, with only the rear bumper being wrapped up. However, there are cues that indicate this is a plug-in hybrid car, like the hidden charging port under the left taillight and regulatory yellow stickers that hybrid prototypes are forced to have on their windows.

The obvious rival to the GT 73 will undoubtedly be the Porsche Panamera Turbo S E-Hybrid, which features a 4.0 litre biturbo V8 that serves up 542 hp (550 PS) and 770 Nm, coupled to an electric motor with 134 hp (136 PS) and 400 Nm. The total system output for the Porsche is 671 hp (680 PS) and 850 Nm, which is less than the upcoming GT 73, and allows for a 0-96 km/h time of 3.2 seconds.