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Nope, their entire stack is JVM based now.

That wouldn't exclude JRuby though

I know they're not using JRuby

That's not the move they made; they moved to Scala. Their original Rails app couldn't scale. They now use Rails on the front end, but the real data isn't Rails. This has been written about extensively:

http://highscalability.com/blog/2013/7/8/the-architecture-tw...

http://highscalability.com/scaling-twitter-making-twitter-10...

The newer link doesn't mention them using Rails anymore. It's probably still in use in some internal apps, but the main twitter.com site should be 100% Scala now.

No, I asked to an engineer last month and their still using their 'Monorail' for twitter.com

Not entire stack, they are still using some parts of the original monorail app in their stack.

This was true as of July 2013. Source: A Twitter Engineer working on the Tweets Service inside their mothership SoA Application.

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