Let's just put it this way, Mercedes added all-wheel drive and still wants a four-door AMG GT before it thinks it can compete.
What the heck was the Porsche Panamera supposed to compete with anyways? When it came out, it was easy to read what the product planners had in mind from the get-go. Take the world's most indisputable sports car champion, the 911, and put four doors on it. But wait, it couldn't just be a performance car with an extra set of doors to allow passengers to actually fit into the rear, it needed to be comfortable too. Not quite Mercedes S-Class comfortable, but enough to appeal to edgier sedan buyers.
Despite its awkwardness the first time around, Generation II of the Panamera seems to have done away with the bulging rear end to become something that actually looks as good as a Porsche should. It's been successful enough to convince Mercedes and BMW to join the fight.
With the Panamera now good and powerful enough to be considered a four-door sports car, Mercedes decided to launch the 800 horsepower four-door AMG GT and BMW has hinted that it'll follow that up with an upcoming replacement to the 6 Series Gran Coupe. Neither is currently ready to race the Panamera, leaving Porsche with a monopoly, but since the four-door AMG GT is likely to be built using the AMG department's latest tech, all featured on the AMG E63 S, pitting the two against each other should give us a good idea of which automaker will come out on top. Keep egging on this German civil war from the sidelines by watching for yourself.