There are no instances in ActivityPub either. There's only actors.
The instance'ification came outside of the work on the spec, though it did start with the particular shape of how sharedInbox was defined. I wish I had pushed harder for sharedInbox to retain the actor-like properties I believed were important, rather than the implicit-routing that Mastodon pushed for. My biggest regret.
Nonetheless, even then, there's still no "instance" in AP, in terms of the spec. In terms of the fediverse, the way it became, that's a different story.
That said, "instance" has become several things on the fediverse, and even though it's not how I have argued things should be, it encompasses several things, including often a kind of community, and also including participatory infrastructure.
I'm not interested in playing the comparison game too much, but there is where we are: ATproto allows for movement across the network, but still does rely on server-oriented sources of authority (and looks like it will get more of it in the upcoming versions of their authorization systems, from what I have read), and the fediverse has developed into a strong sense of server-oriented sources of authority, but is more participatory.
Directed delivery remains an important part of how the fediverse manages to achieve participatory involvement that is still lacking from the ATmosphere's hub-and-spoke-in-practice ecosystem at present. It is how you scale down and wide.
Both could learn from each other, though. Even combined is not the full answer.
Overall I remain *mostly* disinterested in the fediverse-vs-atmosphere debates, because I am not interested in squabbles over the present but building towards a future. It's hard not to make a bit of side commentary though, I guess.
@cwebber agreed.
What's interesting is to see how instance-like structures are evolving in the Atmosphere. Blacksky includes a PDS, AppView, Feeds, and Assembly (as well as a not-user-visible Relay and PLC mirror) ... and with Acorn, is also providing similar structures as a basis to Latinsky etc. Northsky, Eurosky, and Gander are also on the path to instance-like structures.
Of course with PDS's allowing data movement, it's more flexible than the Mastodon et al instance architecture (although ActivityPods highlights that this data movement is compatible with fedi-style instances too); and there are a lot more moving parts (although FIRES and FASP are adding more parts to the fedi model as well). @thisismissem has suggested that the ecosystems are converging in some ways; I'm not so suare about that, but there's definitely cross-fertilization.
Agreed though that even combined it's certainly not the full answer! Still, the prototypes-at-scale are useful for understanding the dynamics with future platforms like Spritely.
But do those convergences seem like crude (and/or crudely implemented) features being bolted on messily? I haven't looked into it, so I don't know, but I can imagine such shoehorning of functionality that doesn't really fit.
