What is cookie deprecation?
Cookie deprecation refers to the decline of third-party cookies, small files set by a domain other than the site a person is visiting. Advertisers have long used them to follow people across sites for targeting, retargeting, frequency capping, and attribution.
Third-party cookies haven't disappeared everywhere. Safari and Firefox block them by default. Google announced plans to phase them out of Chrome but later reversed course and kept them. The practical result is the same for advertisers: cookie-based tracking now covers a shrinking, uneven share of people, and it can't be relied on alone.
What changes when third-party cookies decline?
| Use case | How cookies supported it | What teams use instead |
|---|---|---|
| Retargeting | Recognizing past visitors on other sites | First-party audiences and platform-native signals |
| Conversion tracking | Linking ad views or clicks to later sales | Server-side tracking and Conversions APIs |
| Attribution | Following journeys across sites | Modeled measurement and incrementality testing |
| Frequency capping | Counting exposures across sites | Platform controls and contextual planning |
What is an example of cookie deprecation's impact?
A retargeting pool that kept shrinking
A travel brand built its retargeting on third-party cookies. Over time, visitors on browsers that block those cookies, or who decline them, dropped out of its audiences, and its reporting missed conversions from those visitors.
The brand moved to first-party audiences and server-side conversion tracking, so its signal no longer depended on which browser a traveler used.
First-party cookies vs. third-party cookies
| First-party cookies | Third-party cookies | |
|---|---|---|
| Set by | The site the person is visiting | A different domain, such as an ad tech provider |
| Typical use | Logins, carts, site analytics | Cross-site tracking and advertising |
| Browser treatment | Generally allowed, sometimes shortened | Blocked by default in Safari and Firefox |
| Future outlook | Durable | Declining as a basis for measurement |
Why does cookie deprecation matter?
The headline about cookies matters less than the trend behind it. Between browser rules, ad blockers, operating system changes, privacy regulation, and consent choices, any measurement plan that depends on third-party cookies is measuring part of the audience.
- Build on first-party data. Data a business collects directly is usually the most durable signal it has.
- Send signals server-side. Server-to-server connections are far less affected by browser limits.
- Model what you can't see. Marketing mix modeling and incrementality testing don't depend on cookies.
- Respect consent. Durable approaches still follow consent and privacy rules.
How does Alli do this?
Alli by PMG's Audience Gateway gives brands a first-party, server-to-server path for conversion and audience signals to the major ad platforms' Conversions APIs, from one managed implementation. Because the data travels server to server, it's far less dependent on browser cookies, and platform API changes are handled as part of the service.
Alli Datasources brings first-party systems in next to media data, and Alli Scenario Planner models media response from aggregate spend and sales, which doesn't depend on cookies at all.
Explore Alli Audience GatewayCookie deprecation FAQ
Are third-party cookies going away?
Not everywhere. Safari and Firefox block them by default, while Google decided to keep them in Chrome. Their reach for tracking is still shrinking because of privacy rules, consent choices, and ad blockers.
What is the difference between first-party and third-party cookies?
First-party cookies are set by the site a person is visiting, for things like logins and carts. Third-party cookies are set by other domains, usually for cross-site tracking and advertising.
What replaces third-party cookies for advertisers?
A mix of first-party data, server-side tracking through platforms' Conversions APIs, contextual targeting, and modeled measurement such as marketing mix modeling.
Does cookie deprecation affect measurement?
Yes. Cookie-based conversion tracking and attribution miss more activity as cookies are blocked or declined, which is why teams pair them with server-side tracking and modeling.
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