iOS 11 Ships Intelligent Tracking Prevention

What Changed

WebKit announced Intelligent Tracking Prevention (ITP) in June 2017, and it shipped that September with Safari 11 and iOS 11.¹ Instead of relying on a block list, Safari used a machine learning model, running on the device, to classify domains that had the ability to track people across websites.

Once a domain was classified, Safari limited its cookies. If the user had not interacted with that domain as a site they visited directly in the last 24 hours, its cookies could no longer be used in a third-party context. After 30 days without interaction, its cookies and other website data were deleted.

ITP was on by default for every Safari user, with no setting to opt in. That was the decisive difference from content blockers two years earlier, which only affected people who installed one.

Why It Mattered

Most cross-site advertising on the web relied on third-party cookies: a pixel from an ad network, a retargeting vendor or an attribution tool would recognize the same browser on many sites. ITP broke that recognition for a large share of mobile traffic, because Safari is the default browser on every iPhone. It still is: in September 2026 Safari accounted for about a quarter of mobile browsing worldwide, 46% in the US and 55% in Canada, according to Statcounter.^2,3

Six advertising trade groups published an open letter arguing that Apple's approach would "sabotage the economic model for the Internet".⁴ Apple replied that ad tracking had become so pervasive that it was possible to recreate most of a person's browsing history, and kept the feature.⁵

It also started a cycle that ran for the next eight years. Ad platforms moved their tracking to first-party cookies on advertisers' own sites, and ITP 2.1 capped those too; each later workaround met a new restriction.