We still aren't entirely sure what Porsche is testing with these odd Panameras. It seems way too soon for a refresh. The other possibility is a hotter model that the company might call the Turbo GT. These shots catch the model at the Nürburgring and in southern Europe.

This model wears a revised front bumper with revised intakes. There's also a new inlet at the tip of the bonnet, just above the number plate.

Gallery: Porsche Panamera Turbo GT / Facelift Spy Photos

One shot offers a glimpse into the cabin through the open window. The company has a fabric covering in there, which suggests some styling tweaks. Unfortunately, it's impossible to see what Porsche is changing in this photo.

The rear looks largely identical to other high-end trims of the Panamera with dual oval-shaped exhausts on each side. The lower fascia between the pipes has a vertical rib in the centre.

Our spies claim a Porsche insider confirms the company is working on a Turbo GT version of the Panamera. It would allegedly be the sedan sibling to the recently launched Cayenne Turbo GT. This includes sharing the 4.0-litre twin-turbo V8 that makes 631 bhp (471 kilowatts) and 626 pound-feet (849 Newton-metres).

If this is accurate, then it would narrowly top the latest Panamera Turbo S. It also has a 4.0-litre twin-turbo V8, but this one produces 620 bhp (462 kW) and 604 lb-ft (820 Nm). This is enough power for the vehicle to reach 60 miles per hour (96 kilometres per hour) in 2.9 seconds.

It's not clear when Porsche might debut this meaner Panamera. From the low amount of camouflage, the development appears to be complete. The company would just need to find a hole in the busy product launch schedule to premiere this one.