In the footer it says:
However, in the footer under Company > Legal > '6. Content Permissions, Restrictions, and Creative Commons Licensing' it instead doesn't specify which CC BY-SA licence we're releasing our content under. It also links to the CC BY-SA 4.0 license:
The CC-BY-SA Creative Commons license terms are explained in further detail by Creative Commons, but you should be aware that all Public Content you contribute is available for public copy and redistribution, and all such Public Content must have appropriate attribution.
Since CC BY-SA 4.0 cannot be licensed to CC BY-SA 3.0 if subscriber content is only provided under 4.0, where the footer says 3.0 it can cause users to break the licences.
The footer under Area 51 also mentions that content is licensed under CC BY-SA 2.5.
Since it's not defined which version of the license the content is provided under, I also interpret it to potentially mean all the versions.
What license is subscriber content licensed under?