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Ah yeah, you're right 8 speed won't, but 11 speed should fit on any 9 speed campag freehub.
"all Campagnolo-compatible 9/10-speed freehub bodies also are compatible with Campagnolo 11-speed cassettes
Read more at http://www.velonews.com/2014/07/bikes-and-tech/technical-faq/technical-faq-1011-speed-compatibility_337803#K0S1fAKLVphZ87xT.99"
http://www.velonews.com/2014/07/bikes-and-tech/technical-faq/technical-faq-1011-speed-compatibility_337803
Sumo-
I know they should, but some 9/10 speeds aren't compatible, even if they claim they are. I had a lovely pair of wheels with Tune hubs that become redundant when I moved to 11 speed, as I couldn't get a cassette on them. Tune admitted via email that some of their older hubs weren't compatible.
Most now should be fine though, just be aware that compatibility isn't always guaranteed.
andyp
No you can’t. 8 speed is incompatible with 9/10/11 speed. Some 9/10/11 speed hubs won’t take an 11 speed cassette as the lockring won’t get enough purchase to tighten enough.