Audi is formally unveiling its long-wheelbase 2011 A8 L next week at the 2010 Beijing Auto Show. The company said the fourth-generation flagship sedan is slated to arrive in the U.S. this fall alongside the standard-wheelbase A8, but a new direct-injection 6.3-liter W12 engine won't be available in the States until spring 2011.

The redesigned 2011 A8 was revealed earlier this year at the 2010 Detroit Auto Show. Both the standard- and long-wheelbase models share a variety of hardware, including a standard 372-horsepower 4.2-liter FSI V8, eight-speed Tiptronic automatic transmission and Quattro all-wheel drive.

The new 6.3 W12 that will be shown next week in Beijing ? it replaces the previous 6.0-liter unit ? makes 494 hp and 461 pound-feet of torque. In combination with the eight-speed gearbox, Audi says the A8 L will accelerate from zero to 60 mph in less than 4.9 seconds and on the EU test cycle will return an average 20 mpg. Top speed will be electronically limited to 155 mph.

As with the standard-wheelbase version, the A8 L can be ordered with an optional sport differential and torque vectoring, as well as a choice of 20- or 21-inch wheels. The standard setup includes an adaptive air suspension and 19-inch wheels and tires.

Visually, the A8 L is barely distinguishable from the standard A8, although it will offer optional LED front lighting. The top-of-the-line A8 L W12 gets additional black and chrome exterior trim and twin trapezoidal tailpipes integrated into the rear bumper.

The A8 L is more than 5 inches longer than the A8, while width and height are virtually identical. Most of that extra space between the wheels is devoted to the rear passenger compartment.

The rear doors are longer, for easier entry and exit, and the vehicle can be ordered with two individual power-adjustable seats with heating and ventilation. Among the optional rear-seat amenities are an entertainment system, a full-length console with separate controls for the four-zone automatic air-conditioning, a refrigerator, a folding table and a massaging/reclining seat with power-adjustable footrest.

The cabin is trimmed in leather and wood, and there is a long list of optional equipment, including a twin-panel panoramic glass roof, a 1,400-watt Bang & Olufsen audio system with 19 speakers, and a "navigation plus" system equipped with a touch-sensitive control panel.

Among the available high-tech hardware are adaptive cruise control with stop-and-go, side assist and lane assist, night view assistant with pedestrian detection, automatic emergency braking and the pre-sense safety system.

Audi has not announced U.S. prices, but said the A8 L "will maintain its relative [price] position in the market" against such competitors as the Mercedes-Benz S-Class, the BMW 7 Series and the Lexus LS.