What is the Google Advertising ID (GAID)?

What it does

The GAID performs the same function on Android that the IDFA performs on iOS: it lets two parties recognise the same device at two moments, which is what deterministic attribution requires.

It is resettable by the user, and can be deleted entirely — at which point apps receive a string of zeros rather than an identifier, which is Android's equivalent of an opt-out signal.

How Android's approach has differed

Google took the same destination by a slower route. Rather than a system prompt that gates the identifier for everyone at once, Android kept the GAID broadly available while building Privacy Sandbox as a replacement set of APIs.

The commercial reason is not subtle: Google's business depends on the advertising ecosystem in a way Apple's does not, so a transition with a replacement in place matters more than a fast removal.

The practical consequence for advertisers is that Android measurement has remained more granular than iOS for several years, and that the gap is closing on a published timeline rather than overnight.

What to do about it

• Do not build anything that only works with a GAID. The direction of travel is unambiguous.
• Handle the zeroed identifier properly. Deleted GAIDs are a real and growing share, and code that treats the zero string as a valid identifier will merge unrelated users.
• Invest in the same replacements as iOS — first-party identity, contextual signals, causal measurement.
• Test Privacy Sandbox APIs before you need them, because migration under time pressure is where errors enter.