What Changed
Apple announced the enforcement date a week before iOS 14.5 shipped, after delaying the requirement from iOS 14 the previous autumn.1 The App Tracking Transparency (ATT) prompt applies to any app that wants to track users. Apple defines tracking as linking data from your app with data from other companies' apps, websites or offline sources for targeted advertising or ad measurement, or sharing it with data brokers.
If a user taps "Ask App Not to Track", the app gets an Identifier for Advertisers (IDFA) of all zeros, and it must not track that user by other means. Apple's rules also ban fingerprinting, meaning combining device signals to identify a user, whatever the user chooses.
For measuring ads without consent, Apple pointed developers to SKAdNetwork, its own attribution framework. SKAdNetwork reports app installs to ad networks in aggregate and after a random delay, with only a small amount of information about what the user did next.
Why It Mattered
Mobile advertising had been built on the IDFA. It let ad platforms connect an ad view in one app to an install or purchase in another, target people based on what they did elsewhere, and optimize campaigns user by user.2 Many users declined when asked, so that link disappeared for a large share of iPhone users. Opt-in rates have risen since: AppsFlyer, an attribution company, reported in 2025 that about half of users globally now consent to tracking, so roughly half still can't be tracked.3
The effect was largest for businesses that depended on targeted mobile ads. In February 2022 Meta told investors the change would cost it about $10 billion in revenue that year.4 Advertisers saw higher reported costs per result and far less detailed reporting, especially for app installs.
ATT also raised questions about Apple's own position. Its rules apply to tracking across companies, so a company's use of its own first-party data, including Apple's, is largely unaffected. That distinction, which Ben Thompson examined in "Data and Definitions",5 later drew the attention of competition authorities in France, Italy and Germany.
The privacy gain was real but incomplete. A study by Oxford researchers of 1,759 iOS apps, before and after the new rules, found that ATT did stop collection of the IDFA, but the number of tracking libraries in the apps stayed roughly the same.6 It also found apps computing a fingerprint-based identifier on their servers, in breach of Apple's policies.
Notes
- “Upcoming AppTrackingTransparency Requirements,” Apple Developer News, April 20, 2021, https://developer.apple.com/news/?id=ecvrtzt2. ↩
- Eric Benjamin Seufert, “The End of the Beginning on Mobile: ATT Is Enforced Next Week,” Mobile Dev Memo, April 20, 2021, https://mobiledevmemo.com/the-end-of-the-beginning-on-mobile-att-is-enforced-next-week/. ↩
- “AppsFlyer Shows Mobile Ad Market Thrives 4 Years After ATT,” AppsFlyer, October 27, 2025, https://www.appsflyer.com/company/newsroom/pr/post-att-growth-2/. Vendor data. ↩
- Kif Leswing, “Facebook Says Apple iOS Privacy Change Will Result in $10 Billion Revenue Hit This Year,” CNBC, February 2, 2022, https://www.cnbc.com/2022/02/02/facebook-says-apple-ios-privacy-change-will-cost-10-billion-this-year.html. ↩
- Ben Thompson, “Data and Definitions,” Stratechery, June 21, 2022, https://stratechery.com/2022/data-and-definitions/. On how Apple defines tracking. ↩
- Konrad Kollnig et al., “Goodbye Tracking? Impact of iOS App Tracking Transparency and Privacy Labels,” Proceedings of the 2022 ACM Conference on Fairness, Accountability, and Transparency (FAccT ‘22), Oxford University Research Archive, June 20, 2022, https://ora.ox.ac.uk/objects/uuid:38e54298-23b1-4338-a120-2ba715c0af82. Paper presented at the 2022 ACM Conference on Fairness, Accountability, and Transparency (FAccT ’22). ↩