The biggest changes are at the back, and even those tweaks are quite minor.

Audi doesn't even bother to conceal the S6 during the performance model's testing anymore, possibly due to the incredibly close resemblance with the standard A6. This mix of a spy video and photos of the new model provide a look at all angles of the upcoming four-door.

Gallery: Audi S6 Spy Shots

A very close look is necessary to spot the differences between the A6 and S6. The sporty model as more openings in the lower fascia on the driver's side, but the overall design still looks similar. The differences are a little more striking at the back where the more aggressive four-door features a pair of circular exhausts emerging from each side of the vehicle, rather than the standard model's pentagonal-shaped pipes.

We expect the S6 sedan and its Avant wagon counterpart to use a 2.9-liter twin-turbo V6 making around 450 horsepower (336 kilowatts). If this educated speculation is accurate, the output would be a healthy upgrade over the mild-hybrid 3.0-liter turbocharged V6 making 335 horsepower and 369 lb-ft of torque in all current trims of the A6 in the U.S. Other performance tweaks would include a sharper suspension and better braking. Expect better seat bolstering to hug the front occupants.

If you're looking for more performance, a new RS6 is also on the way. Rumors indicate the latest generation has the same 605 hp (451 kW) as the current Performance model but with a boost in torque to around 590 lb-ft (800 Nm), versus 553 lb-ft (750 Nm) from the existing one.

The new S6 will almost certainly debut in 2019. The RS6 will take longer to arrive, in part to let the milder model put its mark on the segment.

Source: Carpix, Automotive Mike via YouTube