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/2

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/ 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 :)