The GT4 is just a concept, but a production model is coming next year.

Mercedes-AMG plans to celebrate its 50th birthday with a four-door version of the GT. The company's third standalone model debuted this week as a close-to-production concept at the Geneva Auto Show.The concept looks like a stretched GT with two sets of doors. However, the similarities between the two models will only be skin-deep. The sedan will ride on an evolution of the modular MRA platform that underpins a number of recent Mercedes-Benz models including the E-Class, according to British magazine Autocar.

The four-door's platform will feature its own wheelbase and track width; the sedan won't be simply a re-skinned E-Class. It will also make extensive use of lightweight materials like hot-formed steel and aluminum in order to keep weight in check.

The concept is branded as a hybrid, but it is expected that the production model will launch next year with a twin-turbocharged 4.0-liter V8 engine borrowed from the E63. It will send over 600 horsepower to all four wheels via an automatic transmission and Mercedes' 4Matic all-wheel drive system. The lineup could also include an entry-level variant powered by a V6 engine.

The announcement was vague about the possibility of electrified powertrains, promising only that "[...] Mercedes-AMG will develop segment-specific hybrids in the future that will boast impressive performance and maximum efficiency."

Mercedes-Benz claims the concept is an extension of the SLS AMG and AMG GT line of performance coupes, but it will likely act as a replacement for the slow-selling CLS Shooting Brake.

Live photos by Ronan Glon.