I believe the shimano CS-HG800-11 cassette is 11 speed for 10 speed hubs
Otherwise you'd need to machine either the freehub or the cassette as Snottyotter says.
As he said in the question. That HG800-11 is 11-34 anyway, so basically MTB.
Basically but not really. Its listed in the road section of Shimano's tech docs
@snottyotter started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
I believe the shimano CS-HG800-11 cassette is 11 speed for 10 speed hubs
Otherwise you'd need to machine either the freehub or the cassette as Snottyotter says.