Today, the automaker officially announced it's celebrating the 20th anniversary of its A4 model. And why wouldn't it? With ore than 6 million sold, this is currently the best selling Audi of all times and has done a great deal of good over the years. We need only look at the RS4 they built to celebrate the occasion to remind ourselves of why the number 4 has special meaning for any Audi.Having been launched in November 1994, the A4 is quite a young car. However, it's no different to the Mercedes-Benz C-Class, which entered the market in 1993. That's because before that these two Germans were called something else, Audi 80 in the case of the A4's predecessor and 190E in the case of… well, you get the idea.Besides simply celebrating the milestone achieved by its model, Audi also announced that a new model is going to launch next year. The official press statement suggests the famous factory in Ingolstadt is already gearing up for production of the fifthgeneration A4, which will be launched in 2015.Since the A4 is also made at Neckarsulm, Ingolstadt is free to retool itself now. Audi says as many as 1,300 new robots are currently being installed in the body show, suggesting a major undertaking for the so-called B9 generation. It should be ready in time for the Frankfurt motor show, our spy photos suggesting new engines and tech are on the way. How important is this new car for Audi? Crucial, as board of management member Dr. Hubert Waltl points out: “The sporty A4 family is the heart of the Audi brand still today, and is extremely popular with our customers around the world.”More than 700 A4 models are produced every day at the Ingolstadt factory. Another 40,000 units per year are made in Neckarsulm and there are lots more made in Changchun for the Chinese market.