The A8 4.2 rides on a 115.9-inch wheelbase, while the A8 L adds 5.1 inches in both wheelbase and overall length. Both are powered by a 4.2-liter V8 rated at 350 horsepower and come with a six-speed automatic transmission with Tiptronic manual shift control. Both models come with dual-zone automatic climate control that uses temperature, moisture, and infrared sensors to demist the windows before they can even think about fogging. Other standard features include leather upholstery; heated front and rear seats; 16-way power adjustable front seats with lumbar adjustment; interior air filter; power tilt/telescoping leather-wrapped steering wheel with audio controls; cruise control; memory for the driver's seat, mirrors, and steering wheel; heated power mirrors with auto-dimming and passenger side tilt-down back-up aid; power windows and door locks; remote keyless entry; sunroof, Bose AM/FM radio with 6-disc CD changer; Sirius satellite radio; auxiliary audio input jack; navigation system with voice recognition; Bluetooth wireless cell phone link; trip computer; auto-dimming rearview mirror; Homelink universal garage door opener; rain-sensing wipers with heated nozzles; trunklid-closing assist; automatic bi-xenon adaptive headlights with washers; theft-deterrent system; front and rear fog lights; adjustable load-leveling air suspension; front and rear limited-slip differentials; and P255/45HR18 tires on alloy wheels. The A8 L adds manual rear side sunshades. The parking brake is operated by a switch.

The A8 L W12 rides on the 121-inch wheelbase and is powered by the 450-hp W12 engine. It comes with ultra-luxury amenities, including front and rear park assist; power sunshades for the rear windows; power-adjustable rear seats; leather upholstery on the door panels, console and dashboard; rear dual-zone automatic climate control; massaging and ventilated front seats; Alcantara interior trim; wood and leather-wrapped steering wheel; rearview camera; keyless access and starting; door-closing assist; power trunklid; trunk pass-through with a ski sack; and P255/40HR19 tires. The A8 L W12 also comes standard with a full-length rear-seat center console, housing elaborate climate controls and seat adjustments, plus a dual-screen entertainment system; this limits seating capacity to four, though the rear center console can be deleted at no cost in favor of a three-place bench seat.

The S8 rides on the standard 115.9-inch wheelbase, and features a high-performance 5.2-liter V10 rated at 450 hp. The air suspension is firmer, the brakes are larger and the steering is quicker. Extra bright trim and 20-inch wheels with P265/35R20 tires contribute to a distinctive look outside; while inside are sport seats upholstered in two-tone leather, darker wood or carbon fiber trim with aluminum accents, and white-on-gray italic gauge faces.

Option packages for the A8 and A8 L include a Sport Package ($4,300) with firmer suspension settings, 20-inch wheels with P265/35R20 summer performance or all-season tires, and a multi-function leather-wrapped three-spoke steering wheel with shift paddles. A 14-speaker, 1000-watt Bang & Olufsen sound system custom-tailored to the Audi's interior acoustics ($6,300) is available.

Options for the A8 and A8L include adaptive cruise control ($2,100), which uses radar to maintain a prescribed distance from traffic ahead; four-spoke wood and leather multifunction steering wheel with wood shift knob ($690); a solar-powered sunroof panel ($790) that blows cooling air through the car while it is parked (and replaces the standard glass sunroof); front seat massage and ventilation ($1,500); rear-seat electric lumbar adjustment ($350); 19-inch wheels with P255/40R19 all-season tires ($1,900); and, for the A8 L only, a personal refrigerator ($1,500) in the trunk accessible through the rear-seat armrest.

A8 L W12 options are limited to the adaptive cruise control, solar roof panel, four-spoke multi-function steering wheel ($200), Bang & Olufsen stereo, refrigerator, full-leather upgrade ($3,900), and 20-inch wheels with P265/35R20 tires ($3,200).

Most of the stand-alone luxury options offered on the standard-wheelbase A8 are available on the S8 for the same prices. Carbon-fiber interior trim ($550) is available.

Safety features on all A8 models includes 10 air bags, including dual front airbags, front and rear side airbags, curtain side airbags, and front knee airbags. In a crash, computers quickly determine which dual-threshold, dual-stage air bags to deploy, how quickly to deploy them, and how intensely they should be deployed. Also standard are antilock 4-wheel disc brakes with brake assist, traction control, electronic stability control, front-seat active head restraints, and a tire-pressure monitor. A Technology Package ($3,600) adds Audi Side Assist and Audi Lane Assist.