Page not found on GitHub?
https://swift.org/source-code/ https://github.com/apple/swift
They changed their mind.
EDIT: I'm joking of course. More likely, they realized they accidentally forgot to excise some incredibly sensitive private information from the repo's history and are working fast on it before they make the repo public again.
It seems to be down due to traffic.
https://github.com/apple/swift wouldn't appear non-existent due to traffic.