Your sales rep may be your best resource on this - he can check with corporate more readily than you can.
Keep in mind that the GT is built on the 7-series chassis, and things on the 7 and 5 series don't always line up. Sometimes, the 7-series gets it first, sometimes, it depends on the whims of corporate.
April is a nice month to visit...I picked mine up the end of April. It happened to be just after Easter, which has it's good and bad things...lots of things had been closed. Depending on where you plan to go, you may or may not run into snow. Don't get caught in the mountains in a snow storm without snow tires, as there's a really big fine (all season tires or summer ones do not cut it there)! And, if you get stuck or cause an accident, they will fine you. Be prepared for some sticker shock when you fill the car up...it didn't come with a full tank, either!
If you've never driven in Germany before, keep in mind the priority road signs and right-of-way rules...in small towns, the sidestreets often do NOT have stop or yield signs...you have to know who has the right-of-way or you'll cause an accident. Also, there may not be speed limit signs upon entering small towns - it automatically drops to 50Km/h when you cross the rectangular yellow town name sign, and returns to 'normal' (100km/h) when you exit unless there's a sign changing that. The town 'exit' sign is the same as enter with a diagonal line through it. They do enforce their highway rules. One guy I worked with got two tickets going around a curve where he touched the solid line twice...they expect you to stay in your lane, use your turn signals, and merge and yield properly. Traffic circles can be messy, as Germany differs from most European countries. In most, those coming INTO the circle have the right-of-way, in Germany, they have priority signs giving those IN the circle the right-of-way (for the most part). BTW, the priority road sign is an upended square , white background with a yellow square inside. This trumps other right-of-way rules.
The first few days, I hit a couple of (thankfully low) curbs since it was hard to judge the length and turning radius, so be careful on that. It all worked itself out after a few miles. Enjoy! Try not to exceed their recommended 1000-mile break-in restrictions. It may be hard on the autobahn, but the vehicle will reward you in the long term if you do. FWIW, I averaged about 24mpg while there. This included maybe 70 miles at 100mph when allowed, and lots of smaller roads. Gradual acceleration and smooth. I don't drive like that so much now, but felt it prudent at the time.