@jeroenpraat You mean Mastodon started using ActivityPub in September 2017, when Mastodon and ActivityPub both existed and had been released. :-)

MissKey started using ActivityPub in December 2018 I believe -- it's the first changelog item that mentions it:

https://github.com/syuilo/misskey/releases/tag/10.63.0

I have asked before about what MissKey was using before AP, and I believe the answer was that it simply didn't federate.

@lidia_p @liaizon @orrpetrichorr @estragon @clacke