The feature will be on by default in Safari in a release later in 2019, and is available in a preview release now. Apple is hoping to make it a true web standard and has submitted a proposal through the World Wide Web Consortium's Web Platform Incubator Community Group.

Advertisers might not be happy with the technology. Although it still lets them see how ads translate to more business, it would prevent them from tracking habits in real time. They'd have a harder time determining just when and where to run ads. Apple is betting that this is an acceptable trade-off, though. The added privacy might prevent people from resorting to more drastic measures to protect their privacy, like disabling cookies and using ad blockers.