One question that @rwg asks is when Mastodon chose to adopt ActivityPub to replace OStatus. I remember this Tweet from the period:

https://x.com/evanpro/status/851155551325229058

I don't know if anyone else read it, but I remember it being a hard thing to write. I was happy about the work but I felt that OStatus was the past and AP was the future, and I wanted to point new projects in the right direction.