Kevin Montrose is a Stack Exchange developer who writes about the Stack Exchange API, machine learning, and performance work like the Jil JSON library.
HN links it for inside accounts of Stack Exchange engineering, including its API history and machine learning projects.
They have some machine learning projects: https://kevinmontrose.com/2015/01/27/providence-machine-learning-at-stack-exchange/
Also, they do get a lot of comments. You can read about their setup here: http://nickcraver.com/blog/2016/02/17/stack-overflow-the-architecture-2016-edition/
http://nickcraver.com/blog/2016/03/29/stack-overflow-the-hardware-2016-edition/
Here's a post about it from Kevin Montrose (API dev @ SE): http://kevinmontrose.com/2012/02/01/stack-exchange-api-v2-0-no-write-access/