And my favorite, Raverly (~7 mil user accounts), is done by two engineers (or was, not too long ago - it's hard to get numbers on these things). Two! Talk about developer efficiency.
"We use Go at Twitch for many of our busiest systems. Its simplicity, safety, performance, and readability make it a good tool for the problems we encounter with serving live video and chat to our millions of users..." - blog post a year ago.
Do your research before spreading old news.
I was not able to determine when Twitch began doing this, but seeing as their first major growth spurt was on launch, seems unlikely it was before they had to scale Rails to a substantial degree. I was also not able to determine what else they've switched over.
Old news is still relevant information, particularly when that news is "went from zero to ~10m on tech X".
Saying twitch "is in Rails" in 2017 is disingenuous to say the least.
...but Twitch still uses Ruby[1], and was still originally in Rails. It still stands as an example of scaling Rails, even if it no longer uses it.
[1] https://jobs.lever.co/twitch/c795ef2d-2621-4383-8aa1-c85c875...