$ git clone https://github.com/rails/rails.git && cd rails

$ find . -name '*.rb' | xargs wc -l | tail -1

232424 total

Maybe I should have said LOCC (lines of commented code)?

That does include all of their unit tests code though. I wouldn't personally define unit tests as "core" framework code since I can deploy a Rails app without them (they never show up in a stack trace). It's going to come down to your own semantics since Rails wouldn't exist as it is today without them either.

Ahhh, you know what? I just realized I was confused: the diff for rails 4 was about +110,000 / -100,000, that's what I'm remembering that number from. My bad!