They’ve been testing since at least June. That’s when I saw the first reports that they were rolling this out to random users. I just started seeing the notice

They’ve been testing since at least June. That’s when I saw the first reports that they were rolling this out to random users. I just started seeing the notice but I have friends that still don’t see it. It also does not appear when I’m logged in to an alternate account. I suspect they may be showing it to users who they’ve detected using adblockers for a while but that’s just my speculation based on my non-scientific testing.