not entirely related, but has anything happened WRT tumblr and activitypub? or is that no longer being considered?

Tumblr 3.0 launched way back in Nov 2007, when David shut down his software services consultancy to focus entirely on Tumblr: https://davidville.wordpress.com/2007/11/01/tumblr-3/

Internally, the mysql database schema was called "tumblr3" as an artifact from that. Or at least that's the explanation I heard when joining the company in 2010.

I don't think anything was ever versioned after v3. So that means if you're saying this is now 4.0, I guess we should expect the biggest change in 16 years :)