App Tracking Transparency (ATT)
App Tracking Transparency (ATT) is Apple's framework requiring iOS apps to ask users for permission before tracking them across other companies' apps and websites. When users decline, apps lose access to the device's advertising identifier (IDFA) for cross-app tracking.
ATT made cross-app tracking opt-in on iOS, and many users decline, which significantly reduced the signal available for mobile ad targeting and measurement.
Like the decline of third-party cookies, ATT pushed marketers toward first-party data and privacy-preserving measurement they own rather than borrowed device identifiers.
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