[kemenaran]

Which is why they switched to dual OStatus / ActivityPub broadcasting – except for private messages, which are now only sent over ActivityPub.

All of this without breaking compatibility across instances running different versions; quite a nice piece of engineering IMHO.

[rogerbraun]

this doesn't make much sense. The very easy way to add AP-level privacy to ostatus was to just use a different salmon endpoint for private messages. This way, messages would never have federated to servers that don't respect privacy settings (by accident. if the server leaks on purpose, that's a different story).

This solution was discussed at length with mastodon devs before the implementation of the private messages. It was ignored. Now we have a situation were Mastodon is likely to switch off OStatus soon, leaving behind all those projects that don't have the dev resources to rewrite their core federation systems every few years.

The Ostatus/AP dual stack is also pretty hacky and not even valid according to the AP spec, although it's getting better all the time.