Seems to be the case of now https://stackoverflow.com/help/licensing .

One of the more recent features added to SO was a timeline of activity and within the timeline you can see which license each the question is under. Here's an example for a random question https://stackoverflow.com/posts/49083680/timeline .

It's kind of weird that while the questions have a license declared the answer don't ... not sure what that's all about.

They're already periodically sending a snapshot to The Internet Archive: https://archive.org/details/stackoverflow.com

They can’t legally retroactively change the license on existing content though - and as soon as they change their EULA to say “You irrevocably assign copyright on your postings to us” then they’ll lose their thought-leader users - and the rest tumbles.

Experts exchange was NEVER the place to get answers. They just perfected the SEO so that Google would point to them first. But everything was behind paywalls and it was never useful.