AT protocol doesn't federate the way ActivityPub does. There are separations between how your dat is stored, how it is aggregated, how it is filtered, and how it is displayed. Each part can be hosted separately and federate differently with separate instances of each part. The aggregation part is the thing that is most critical and there are probably some limited independent instances of that, but BlueSky has offered no support in facilitating this beyond making their peices AT Protocol compliant. You van take what BlueSky built and try to run your own instance of the aggregation service but they provide no documentation or support. You could also build your own, but that's difficult and I don't think anyone is trying.

So it is federated, but pretty much no one is interested in doing the work to federate with the primary infrastructure.