The ap-next developer guide was removed from the https://activitypub.rocks website: https://github.com/swicg/activitypub.rocks/issues/63 (by the father of the Fediverse, no less).
The reason:
It's a fork outside the SocialCG.
This is utter nonsense. The guide refers to the original ActivityPub specification and even to SocialCG reports covering Webfinger and HTTP signatures. The other ap-next project is NomadPub - a collection of FEPs that significantly expand the capabilities of the protocol but don't diverge from the original spec.
However, since dissenting opinions about the present and the future of ActivityPub are now openly censored, a fork may indeed be necessary.
