What it does
Since iOS 14.5 (2021), an app must show the ATT prompt and receive permission before it can access the device's advertising identifier (IDFA) or otherwise track the user across apps and sites owned by others. If the user declines, tracking isn't allowed.
Impact on app marketing
- Less user-level data for targeting and attribution.
- More reliance on SKAdNetwork / AdAttributionKit and on aggregated, modeled data.
- Higher and harder-to-measure cost per install for many advertisers.
Tips for the prompt
- You may show your own explanation screen before the system prompt, explaining the benefit honestly.
- Time it well — after the user understands the app, not on first launch.
- Apple's guidelines forbid rewarding users for allowing tracking.
Example
A game shows a short screen "Allow tracking to keep the game free and see more relevant ads" before the system prompt; its opt-in rate is noticeably higher than when it showed the prompt on first launch.