my takeaway is that I'm impressed they're running such a large scale on scala/JVM. I was at a retail startup in the mid 2010s that was doing their own 3PL, $500m / year and the JVM was a constant pain while scaling up.
Also, there are more large companies running on way more "shoddy" technologies like Rails, which Twitter also used up to some point.
Yet, such a pain in the ass…