Lexus GS

What It Is: A completely undisguised Lexus GS sedan prototype decked out in high-performance, F-style gear. Lexus’s high-performance F sub-brand is similar in concept to BMW’s M or Mercedes-Benz’s AMG, but has thus far only churned out the IS F sedan and the LFA supercar as full-fledged models, as well as a passel of F Sport–branded trim levels for theIS, GS, and LS. Currently, the GS sedan lineup consists on the GS350, GS350 F Sport, and GS450h hybrid.

Why It Matters: If this test mule indeed previews a production GS F sedan, it would continue the mainstream expansion of Lexus’s F sub-brand, which will also launch the RC F—the F variant of the IS’s coupe sibling—next year. Furthermore, a true supersedan from Lexus finally would give its customers an alternative to stuff like the M5, the E63 AMG, or the Audi S6.

Platform: The GS F would get a completely worked-over chassis, and perhaps even some enhancements to the body structure to further stiffen things up. You can count on the sedan spending a decent amount of time circling Germany’s Nürburgring circuit, because, well, you can’t put out a performance variant anymore without claiming it was tuned on the ’Ring. Visually, the GS F will be set apart by subtly pumped-up styling, some of which is visible in these photos. The stacked exhaust finishers are an F signature, and the rear diffuser element and rear lip spoiler are spicier than even those of the GS F Sport. The front of the car can’t be seen in these shots, but look for the front clip to get sassier.

Powertrain: When our spy photographers recently captured the smaller RC F coupe testing, they managed to snag a video of the car in motion. The audio for that clip seemed to indicate eight-cylinder power, which could mean a V-8 will slide into the larger GS F, too. Currently, no GS offers more than six cylinders. An eight-cylinder engine would go a long way to differentiate the GS F and give it a fighting chance at taking on the M5, S6, and E63 AMG, all of which are powered by twin-turbo V-8s. We expect the Lexus to be rear-drive, but it could potentially incorporate theGS350 AWD’s four-wheel-drive components to better match up with the S6 and E63 AMG 4MATIC.

Competition: Audi S6, BMW M5, Mercedes-Benz E63 AMG.

Estimated Arrival and Price: This GS F prototype seems pretty far along in its gestation, which indicates its reveal is just around the corner. We expect a debut next spring, and it should hit dealer lots a few months later as a 2015 model. Expect to pay a hefty premium over the GS350 F Sport, with the starting price approaching $70,000.