Xbox One and Xbox360 parties

Party wise, a way is for your friend to use the xbox app with a earphones or a headset that works through the device and then he joins your party or you join his that he starts up from there.

I believe if the user on xbox one has a backwards compatible game you are able to add there xbox 360 account and join the party but only while playing said gsme.

There are several solutions:

For Party chat, you can start any backwards compatible Xbox 360 game on your Xbox One, and then initiate or join a party with them through the Xbox 360 dashboard (accessible on the Xbox One by pressing View and Menu buttons (the small buttons left and right
of the Xbox button on the controller) at the same time).

Alternatively, your friends can use the Xbox App on a Windows 10 PC or Xbox App on a compatible smartphone to join your Xbox One party.

As for playing on the "same game server", you would need to play the Xbox 360 version of their game.

So for example, if your friends play FIFA [insert year number here] on the Xbox 360, you can NOT join them by starting the Xbox One FIFA [same year number here].

Also, if your friends play Halo on the Xbox 360, you can NOT join them by launching the game in the Master Chief Collection.

However, if they start a game that is on the
Xbox One Backwards Compatibility list, and you do have the Xbox 360 version of the game on your Xbox One, you can play on the same server as them.

To play a BCG, Yes.

Sometimes I play Reach on my Xbox one, and join some friends party chats.

So yeah, you can.

Hello Bug,

Thanks for coming to the forums with your question. You can
view this guide for help with this issue. Basically you are able to if you do it through the Xbox 360 emulator.

In an Xbox 360 game, send game invites and start parties the way you would on Xbox 360: using the Xbox Guide. Open the guide by pressing the
View button and Menu
button at the same time, then choose Friends or
Party and follow the instructions.

Thanks,

Brad