I do not know. I recall hearing you do not, but I don't have 1st hand knowledge (i.e. my 10spd stuff has 10spd shifters and RD). I bought the 11spd group, just had to switch some parts and I do know my 9spd front ring will not work.
A 10speed cassette will work pretty well in an 11speed setup. If you adjust each limit screw, you can hardly tell. Without screw adjustment - they work.
But that assumes you have an 11spd setup and want to use some 10spd stuff.