The Mercedes-Benz CLS, the slope-roofed four-door its maker insists on calling a coupe, has spurred an unlikely rush to fill its dubious niche. Jaguar and Volkswagen are working on similar vehicles, and now Audi is readying one, too. The Audi A7 aims to squeeze into the slender space between the A6 and the A8. Which of the two will it be based on? Neither. Instead, the upcoming Q5 crossover is the donor car-not because of the its body architecture, which is more SUV than passenger car, but because its oversize wheels make a perfect start for a new set of proportions that mix SUV and coupe elements. To separate the A7 from SUV-style crossovers, Audi has opted for a three-box shape. The creative team also favors frameless doors, a partial glass roof, and a four-seat interior. Beneath the unusual skin will be rear-biased Quattro all-wheel drive, a DSG transmission, and engines ranging from a 3.0-liter V-6 to a V-10. The V-10 will be offered in normally aspirated and twin-turbo form for the S7 and the RS7, respectively.