Currently, the A8 offers a choice of two turbocharged V6 engines: a 3.0-litre petrol developing 335bhp (badged 55 TFSI) and a 3.0-litre diesel with 282bhp (badged 50 TDI). We have experienced the latter previously in the Q7 SUV and it remains just as brilliant in the A8; with 443lb ft of torque available from low in the rev range, performance is remarkably brisk and overtakes largely effortless.
And don't think that being a diesel it'll be a noisy beast; the 50 TDI is free from vibration and relatively subdued even when pushed hard, so we'd rate it the pick of the range. But for those worried about the future implications of purchasing a diesel, the petrol makes a wholly convincing alternative.
The 55 TFSI may not have quite the same level of low-down grunt as the diesel, but it still feels perfectly suited to the A8. Its power delivery is buttery smooth and you barely hear anything. It's a characteristic that becomes even more evident in Efficiency mode; lift off the accelerator at motorway speeds and the engine turns off automatically, allowing the car to enter a fuel-saving 'coasting' mode. And with the A8's 48V electric motor available to power all the auxiliary functions, such as the air conditioning and power steering, it can coast for up to 40 seconds before the engine comes back on, entirely unnoticed.
When you want to push on and utilise the petrol unit's performance, it revs more keenly and offers greater outright pace than the diesel, although the equivalent petrol in the Mercedes-Benz S500 is even more responsive and quicker still. Whichever engine you choose, you get a standard smooth-shifting eight-speed automatic gearbox.
Of course, power is nothing without control, and the A8 is a long and relatively heavy car. However, Audi’s quattro four-wheel drive system comes as standard on all models and provides supreme all-weather traction and reassurance compared with rear-wheel-drive versions of the S-Class and BMW 7 Series.
There’s also the option of four-wheel steering. At low speeds, this steers the rear wheels in the opposite direction to the front ones, improving manoeuvrability and making the A8 feel shorter than it is in tight spots, such as multi-storey car parks; at higher speeds, the wheels move in the same direction for greater stability. As a result, the A8 fills you with confidence and proves just as easy to drive in town as it does on the motorway.
While it is easy to drive and decidedly sure-footed, if you're a keen driver you'll find an S-Class or 7 Series more entertaining to pedal down a country lane, because press on and the A8's big body wallows more on its standard-fit air suspension than those better-tied-down rivals.
But, of course, pointy handling is not really its primary purpose, and the A8's softer bent has a more important upside: it's not only the best-riding car in its class, it's also one of the best-riding cars full stop. It simply glides along any stretch of road seemingly untroubled by all but the very worst road scars, so whether you’re sitting in the front or the back, you’ll enjoy unparalleled levels of comfort.
There will, perhaps, be even greater comfort on offer with the optional active suspension system. This scans the road ahead and alters the dampers and springs for each wheel individually accordingly to upcoming bumps but, unfortunately, it’s not available just yet, so we've not had an opportunity to try it.
Granted, on 20in wheels the A8 lets in a hint of road noise over coarse surfaces, but wind noise is kept to a minimum at 70mph. If you want even greater separation from the outside world, you can option double-glazed side windows for a reasonable cost.
What about the autonomous tech? After all, the A8’s USP is that it offers Level 3 autonomy, meaning it allows the driver to focus on other activities in certain circumstances while the car drives itself. Well, that tech isn’t available yet. Indeed, you’ll have to wait until later in 2018 for such gizmos.
We have had a chance to sample a pre-production version of the parking and remote garage pilot, which allows the driver to park their A8 without being in the car. It works through an app on your smartphone, letting you ‘drive’ the car into a space while the A8's sensors, cameras and radars ensure it doesn’t hit anything. We have tested similar technology in the Tesla Model S, but the A8's system is capable of making far more complex manoeuvres. It's a genuinely convincing piece of kit and bodes well for further artificially intelligent technology in the future.