18 months late you can finally winterize your Grail.
(Realise this is of no interest to most people)
They come in both sizes 700c & 650b (29" & 27.5") but typically for Canyon the 700c is sold out and Canyon live chat just told me they would be back in stock in January, which in Canyon-time is May.
Irritatingly I've just bought a set of SKS Edge mudguards to try to fit, and I'm wondering whether it's worth the many hours of fettling for one winter or send them back, wait and probably miss the winter for the Canyon ones. They do look good. It'll be a total pain in the arse to fit conventional fenders with no brake bride and an elevated boss on the seat tube. Sounds like I've convinced myself to wait!