I'm almost certain that Twitter is still using Rails in parts of the stack (they replaced the messaging bus with Scala, or something of that sort). Most importa

I'm almost certain that Twitter is still using Rails in parts of the stack (they replaced the messaging bus with Scala, or something of that sort). Most importantly, a single Mastodon instance is not supposed to grow as big as Twitter. Lots of smaller instances don't have to deal with the same load as Twitter alone.