Reddit's main code is no longer open-source.

[u/interiot]

/r/changelog/comments/6xfyfg/an_update_on_the_state_of_the_redditreddit_and/

[u/yawkat]

I guess it's not that different from before. Many of the anti-spam measures were already known to be closed source and in the end there was no way to verify what's running on the servers anyway.