I don't see how AI needs StackOverflow anymore.

It can either examine the ground truth source code to answer your question "How to expire cookies using RoR Devise gem" or it can read docs for you or it can spin up local experiments to black box examine some software. If humans had done that before posting on StackOverflow, the question never would have made it there.

Its reasoning ability is long passed hoping an example exists online for it to copy.