Spacer with 10s Cassette and the hub is most likely 11s compatible.
Not convinced by this. My Deore XT hubs won't fit 11 speed but need a spacer for 10. I was surprised.
Shimano 11 speed MTB cassette is different to 11 speed road cassette, the former can be mounted on 10 speed hubs.
@graunch started
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Spacer with 10s Cassette and the hub is most likely 11s compatible.