Xbox one and Windows 10's Crossplay not working.

My friends and I, are unable to join each other in private worlds. (Not the public servers that are featured). They are running on version 1.2.0.20 on xbox, I have tried inviting them via Xbox live, They have tried inviting me, and it does not work. I have port-forwarded and I am on beta, so are they, they are "Unable to join world".

Is this a bug or is cross-play in private worlds not out.

Update: Windows 10 players can join Xbox one worlds only, Xbox one cannot join window 10 worlds.