The car has been commissioned by a customer in Europe and is thought to have a price tag of at least €350,000 (£280,000).
It measures 6.36m long, with a wheelbase of 4.22m, and the manufacturer says other customers have already shown an interest in the product.
No small-scale production is planned, although Audi has said other customers will be able to purchase duplicates of the car, but only while the current generation of A8 remains on sale. The next generation is scheduled to arrive next year.
The model, which can seat six people, has a 2.4m glass panel in the roof and a quoted unladen weight of 2418kg, some 323kg more than the standard 4.2-litre diesel Audi A8 L.
The car, which took one year to develop, has been completely reworked from the A-pillar backwards, with extra aluminium braces added in the roof and sills.
It is powered by a 306bhp 3.0 TFSI petrol engine paired with an eight-speed automatic gearbox and Audi's quattro all-wheel drive system and is capable of hitting 62mph from rest in 7.1sec. Top speed is electronically limited to 155mph.
The car runs on 19 in wheels and gets firmer anti-roll bars and brakes from the Audi S8, but the air suspension is unchanged.