I think most miles of Autobahns have a speed limit, there are few sections left without the speed limit.
So it would seem a am wrong after i little googling.
WIKI.
"German autobahns have no federally mandated
speed limit for some classes of vehicles.
[1] However limits are posted (and enforced) in areas that are urbanized, substandard, accident-prone, or under construction. On speed-unrestricted stretches, an
advisory speed limit (
Richtgeschwindigkeit) of 130 kilometres per hour (81 mph) applies. While going faster is not illegal as such in the absence of a speed limit, it can cause an increased liability in the case of an accident; courts have ruled that an "ideal driver" who is exempt from absolute liability for "inevitable" tort under the law would not exceed
Richtgeschwindigkeit."
Visual.
http://www.autobahn-speedhunter.com/