It's not. As https://developers.facebook.com/docs/chat/ explains, "Facebook Chat should be compatible with every XMPP client, but is not a full XMPP server. It should be thought of as a proxy into the world of Facebook Chat on www.facebook.com.
Er, so isn't that the exact same situation as Google? You can still connect with any XMPP client, but XMPP support is now just a proxy into the world of Hangouts.
Yes, my pidgin is working just fine right now. You have to log in through a google account now, you can't connect through a federated account, but AFAIK all previous XMPP clients still work just fine.
It supports client federation, not server federation. Server federation is what it allows XMPP servers to send messages between each other, while client federation allows for other clients to connect over XMPP.
What I don’t quite get is how server federation is much more difficult than ‘client federation’. s2s XMPP looks extremely similar to s2c XMPP, and since they still have s2c XMPP, they don’t seem to have a problem with only exposing parts of their architecture via XMPP.
Really, I can only think of laziness and trying to build a walled garden as reasons to support c2s but not s2s connections.
Both of which are not exactly good explanations for one of the largest companies in software engineering.
As stated by Google officially, and by all accounts of everyone using external clients, XMPP works fine. Federation doesn't, just like with Facebook as mentioned above.
