Example of two Piefed instances that currently federate hexbear:
- https://piefed.zip/instances?page=9&filter=federated&search=
- https://piefed.au/instances?page=6&filter=federated&search=
- https://anarchist.nexus/instances?page=4&filter=federated&search= , which is related to https://lemmy.dbzer0.com/, also federated with hexbear
List of Piefed instances that currently defederate hexbear:
- https://piefed.blahaj.zone/ , the same way https://lemmy.blahaj.zone/ does
- https://piefed.world/, the same way https://lemmy.world/ does
- https://piefed.ca/, the same way https://lemmy.ca/ does
- https://feddit.online/, the same way https://fedia.io/ does (by the way, Fedia isn't a software, it's called Mbin, and doesn't have such code, so not sure why you're including them into your title)
- https://quokk.au/, it used to be the same when it was still a Lemmy instance
- https://piefed.europe.pub/, the same way https://europe.pub/ does
https://piefed.fediverse.observer/list
As you can see, instances defederating hexbear are instances managed by teams which were going to do so anyway, as they already did on Lemmy.
Instances who want to federate know how to do so, there are three examples.