Apple introduced App Tracking Transparency in iOS 14.5, which began rolling out in late April 2021. By the time of WWDC 2021 in June, the first reasonably solid data on what the change was doing to mobile advertising was starting to arrive. The numbers told a clearer story than the marketing on either side had.
App Tracking Transparency required apps to ask users for permission before tracking them across other apps and websites for advertising purposes. The prompt that appeared was not subtle. It asked the user to either allow tracking or ask the app not to track. Across most categories, the share of users who chose to allow tracking was around fifteen to twenty percent. In some categories it was lower.
What this meant practically was that the advertising infrastructure that had grown up over the previous decade, which depended on identifying individual users across different contexts to build profiles for targeting, suddenly lost access to that identification for the majority of iOS users.
The companies most affected were those that depended heavily on Facebook ads to acquire customers. Facebook itself was significantly affected because its advertising platform depended on the same cross-app tracking. Smaller advertisers, who had built businesses around the precision of Facebook targeting, found their unit economics changing rapidly. Customer acquisition costs went up. Ads stopped finding the people most likely to buy the way they had before.
The effects were uneven. Performance for some advertisers and some categories was relatively stable. For others, the change was severe enough to require fundamental restructuring of marketing strategies that had worked for years.
What WWDC 2021 added to the privacy story was further extension of similar ideas. Mail Privacy Protection blocked email tracking pixels. iCloud Private Relay obscured browsing patterns from network providers. The trajectory was clear. Apple had decided to position itself as the privacy-focused alternative in mobile and was making product decisions consistent with that positioning.
The broader question was about who had standing to make these privacy decisions on behalf of users. Apple framed it as user choice, with the user being asked at the appropriate moment. The advertising industry framed it as Apple making decisions that affected an entire economy of small businesses without giving them meaningful input. Both framings had merit. Neither was the whole picture.