Just a heads up for anyone else who watches in 4K HDR, there seems to be a bug in the Amazon app on Samsung Tv's (8000 series atleast).
If you select The Grand Tour straight from the splash page, it takes you to a Ultra Hd version, but not HDR! it doesn't say anything about it and when playing it's not HDR.
If you go to the specific Ultra Hd 4K section on the app, and then select The Grand Tour, then it says it's HDR, and when playing it clearly states it's now plying in HDR..
Odd bug, maybe tv specific, haven't tried the app on pc or xbox but worth keeping an eye out for.