What is App Tracking Transparency?

Apple's iOS framework, from iOS 14.5 in 2021, that requires apps to ask permission before tracking users across other apps and sites, gating access to the IDFA.

How did ATT affect advertising?

Most users opt out, so deterministic cross-app tracking and attribution largely stopped on iOS, pushing the industry toward SKAdNetwork, modelled conversions, and first-party data.

ATT is the permission prompt that limits user-level tracking; SKAdNetwork is Apple's privacy-preserving framework for measuring app installs in aggregate.

Growth Marketing Glossary

App Tracking Transparency

App Tracking Transparencyproper noun

The prompt that rewired mobile advertising — most users said no, and the identifier went dark.

Schematic — the ATT permission prompt

Owner: Apple
Launched: iOS 14.5, 2021
Mechanism: mandatory opt-in prompt
Gates: the IDFA identifier

Forms & parts of speech

ATT · proper noun

Apple's required prompt to track a user across apps.

"Post-ATT, most users opt out, so the IDFA is rarely available."

What ATT changed

App Tracking Transparency, rolled out in iOS 14.5 in 2021, forces every app to show a standard prompt before tracking a user across other companies' apps and websites. Decline, and the app cannot access the device's advertising identifier, the IDFA.

Most users decline. With the IDFA mostly unavailable, the deterministic user-level tracking that powered mobile ad targeting and attribution largely went dark — the single biggest shift in mobile advertising measurement in years.

How the industry responded

The response was a move from individual tracking to privacy-preserving and modelled measurement. Apple's own SKAdNetwork provides aggregate install attribution, and platforms lean on modelled conversions and server-side signals.

For marketers, the practical effect is less precise targeting, harder iOS attribution, and a premium on first-party data and incrementality testing. The clean per-user funnel of the pre-2021 era is gone on iOS.

Worked example. Suppose an advertiser used to retarget iOS users who viewed a product but did not buy, matching them by the IDFA. After ATT, most of those users opted out, so the identifier is missing and the retargeting pool collapses.

The advertiser shifts to broader contextual targeting, SKAdNetwork for install measurement, and first-party signals through the Conversions API. The campaign still runs — but on modelled and aggregate data rather than the per-user trail ATT removed.

Failure modes to watch. Assuming iOS attribution is as precise as before ATT; comparing pre- and post-2021 mobile performance without accounting for lost signal; and neglecting first-party data and incrementality, which are now the durable measurement base.

Benchmarks

ATT opt-in rates vary by app and prompt design but run low overall. Treat any opt-in figure as directional and plan for mostly-missing identifiers.

Live since

iOS 14.5, 2021

Opt-in rates

low

Effect

IDFA mostly unavailable

Ranges are illustrative; every published figure is cited from a named public source or labelled “RGM analysis.”

Synonyms & antonyms

Synonyms

ATTtracking transparency

Antonyms

IDFA

Usage trends

Search interest for this term over the last five years:

View interest-over-time on Google Trends →

Common questions

What is App Tracking Transparency?: Apple's iOS framework, from iOS 14.5 in 2021, that requires apps to ask permission before tracking users across other apps and sites, gating access to the IDFA.
How did ATT affect advertising?: Most users opt out, so deterministic cross-app tracking and attribution largely stopped on iOS, pushing the industry toward SKAdNetwork, modelled conversions, and first-party data.
ATT vs SKAdNetwork?: ATT is the permission prompt that limits user-level tracking; SKAdNetwork is Apple's privacy-preserving framework for measuring app installs in aggregate.

Related tools & calculators

toolCAC calculator
toolRGM benchmarks compendium

Resources & people to follow

referenceApple — App Tracking Transparency (developer.apple.com)
referenceAdjust — mobile measurement after ATT

Curated, non-competitor resources verified per term.

Sources

trendsGoogle Trends — "app tracking transparency"