According to Stack Exchange and Stack Overflow have moved to CC BY-SA 4.0, subscriber content is now licensed under version 4.0 of the Creative Commons license. The change is reflected in the footer of each Q&A site:
user contributions licensed under cc by-sa 4.0 with attribution required.
The footer has been adjusted on other sites as well, e.g. the API. However, the Stack Exchange Data Explorer still has the old footer referring to version 3.0 of the license:
user contributions licensed under cc by-sa 3.0 with attribution required
Is this an oversight or was this intended? Also, Area 51's footer already links to 4.0, but it's named 'cc-wiki' instead, which is a bit confusing.