But in the reddit comments for the OP, the author of this article sheds some light:
> "Hey, author here! I chose to skip that part just because when I was researching our new API, I read so many posts just like that about how great GraphQL is. So I thought it might be more interesting to hear about some of the mechanics of executing the swap and making sure things didn’t go wrong in a production app."
> "But I will say that our previous API, while it worked well for years and enabled huge amounts of growth in our client codebases, was written in a language that was made up at OkCupid that came with our custom web server, so that’s one good reason to switch!"
https://www.reddit.com/r/reactjs/comments/jthwdz/moving_okcu...
I'm interested to see how large companies do these types of migrations, but for me, the more interesting story would've been how on earth some custom language was invented and used for a REST API and what they did to migrate _that_.