A discussion at https://news.ycombinator.com/item?id=12112352 about https://twitter.com/phlsa/status/754337623964053504 and a change: with some reporting it was opt-out for them. A web search turns up earlier pages mentioning this from the late June early July period. Some saying it is supposed to be opt-in and at least one saying there will be a phased rollout. Check things out if you are affected/interested.
Going to trust a reputable source instead of a random tweet, which states it's opt-in: https://www.wired.com/2016/06/latest-ad-tracking-move-google-gets-opt-right Besides, pretty much anyone using a Google account that is privacy conscious has already disabled ("paused") Web & App activity.
My intention was to communicate contradictory information on the its opt-in vs its opt-out aspect. I saw some (check ycombinator thread for example) saying it is being handled in an opt-out manner but others (that Wired article for example, which I had seen) saying it is supposed to be handled in an opt-in manner. I made a mistake though, and typed an "opt-out" where I meant to type "opt-in". I just fixed that and underlined the place I'm talking about. Apologies everyone. As for the contradictory information, the different possible explanations are obvious. One of them being: there could be a glitch which has resulted in unexpected changes and/or non-uniform handling. So some may want to take a look at it (again).
True. Anyone with a Google Account would benefit from checking and updating their security and privacy settings and account preferences. https://myaccount.google.com/intro