Beginning in Model Year 2013, ZIPP wheels were produced as 11-speed and backward compatible to 10-speed.
Wheels produced before Model Year 2012 are not compatible with an 11-speed conversion, and freehubs are not available.
The older silver hubs are too narrow internally and lack the correct flange shape for conversion parts and wheel re-dish.
Only Zipp 188 v7 rear hubs from the model year 2012, which are Falcon Grey or Black with a red endcap, are convertible to 11-speed.
If you have a black or dark grey hub from 2012, it will need the conversion kit installed and the wheel re-dished for 11-speed. This work is usually done at the ZIPP Tech Center as the wheel will need to be de-tensioned. Due to age, a new wheel may be recommended.