Humm, interesting, but I guess it was just some experiment. I had a look on their techblog and see no mentions of crystal All posts | SoundCloud Backstage Blog
And in this post from 2 years ago Learning Scala at SoundCloud | SoundCloud Backstage Blog the author mentions that most of their microservices are written in Scala. That’s interesting too because I thought people were avoiding Scala after all the breaking changes from 2 to 3.