Which Q&A sites in the Stack Exchange network don't participate in Winter Bash?
The following Q&A sites don't participate in Winter Bash 2018 or 2017. They can be recognized by not having the snowflake in the top bar, and the fact that they don't appear in the Winter Bash leaderboard.
- MathOverflow – they have never participated at all since they were migrated to Stack Exchange 2.0 in 2013, according to this Meta post.
- CS50 - this is in several aspects (e.g. privilege levels) a private beta, and private betas don't participate in Winter Bash.
- The sites hosted by Stack Overflow for Teams don't participate in order to keep activity there private.
Additionally, the Iota site didn't participate in Winter Bash 2017 since it was still in private beta when Winter Bash 2017 started.
Data from earlier editions of Winter Bash is incomplete/non-existing, but it is known that sites that were in private beta at the time a specific Winter Bash started didn't participate in Winter Bash that year.