SO seems different because the author of the post is republishing it. If they are republishing copyrighted material without notice, it seems like the SO author is the one in violation of copyright.

In the LLM case, I think it’s more of an open question whether the LLM output is republishing the copyrighted content without notice, or simply providing access to copyrighted content. I think the former would put the LLM provider in hot water, while the latter would put the user in hot water.