Official fuel numbers are 11.4 L / 100 km city, 7.7 L highway, though in a cold week of mixed driving, I averaged around 13.4 L / 100 km, and never got lower than 10.3 on the highway. (driving.ca)
My week of mixed driving netted 12.4 L / 100 km. (driving.ca)
We averaged 15.2 mpg after a week of mixed driving and every AMG GT is subject to a $ 1,000 gas - guzzler tax. (kbb.com)