I read the entire sub-tree under this comment and still cannot figure out what exactly Facebook is written in. Is this because nobody at Facebook actually knows

I read the entire sub-tree under this comment and still cannot figure out what exactly Facebook is written in. Is this because nobody at Facebook actually knows what the entire stack looks like or because they keep it a secret? With their "Move fast, break things" motto I can only shudder at the imagination of the scenarios happening at Facebook HQ: "Hey, so you are the new developer in town? Can you build service X which service Y and Z can use? Just write a proper API, we need this ASAP." - "So what do I write this service in? Any framework already build to support these operations?" "Pick your poison! Check our internal repository collection and see if you can re-use anything useful. As long as we can communicate with it via the API!"