Intent to Extend Experiment: Cookie Deprecation Label Throughout 3PC Phaseout

[John Delaney]

Contact emails
john...@chromium.org, wande...@chromium.org, lin...@chromium.org

Explainer
https://github.com/privacysandbox/tpcd-labeling/blob/main/cookie_deprecation_labeling_explainer.md
https://developer.chrome.com/en/docs/privacy-sandbox/chrome-testing

Summary
With the end of Chrome-facilitated testing period, we will continue to expose cookie deprecation labels within Chrome to facilitate evaluation of the Privacy Sandbox Relevance and Measurement APIs by ad-techs until sometime during the third-party cookie phase-out process in 2025. Third-party cookie phase-out is subject to addressing any remaining concerns of the UK Competition and Markets Authority (CMA).

We will be extending the current set of labels, documented on the developer blog (https://developers.google.com/privacy-sandbox/relevance/setup/web/chrome-facilitated-testing). We are still evaluating possible changes to the labeling configuration in this period between facilitated testing and third-party cookie phase-out. Further guidance will be provided in the coming milestones on any changes to labels.

We expect to support labeled browser groups until we begin phasing out third-party cookies in early 2025, and for some time during the phase-out process.
 
Link to “Intent to Experiment” blink-dev discussion
https://groups.google.com/a/chromium.org/g/blink-dev/c/3escBQGtIpM/m/ntcytva5BgAJ
https://groups.google.com/u/1/a/chromium.org/g/blink-dev/c/v3PiIzm1M-Y
 
Goals for experimentation
While the Chrome-facilitated testing period concluded at the end of H1, we expect ad-techs to continue to use the labels to evaluate and optimize deployments of the Privacy Sandbox Ads APIs.

Experimental timeline
This feature was previously approved to run from Chrome 119 -> 126. We expect to extend this experiment every 3 milestones (per standard process) until some point during third-party cookie phaseout.

We would like to start with extending this for Chrome 127 through 129. 

Any risks when the experiment finishes?
Minimal, the cookie deprecation labels are only available for a subset of users and must be requested. 

We expect to support labeled browser groups for some time during the third-party cookie phase-out process. In this case, the fraction of labeled browsers would increase, which was not the case in the original Intent to Experiment. We will seek approval for this in subsequent Intent to Extend Experiments, and plan to maintain a holdback group at those times.

Any changes in usage/availability will be communicated beforehand to blink-dev.

Reason this experiment is being extended
We have received feedback that these labels are useful for ad tech companies to evaluate the APIs with limited browser groups beyond the Chrome-facilitated testing period.

Ongoing technical constraints
None

Will this feature be supported on all five Blink platforms supported by Origin Trials (Windows, Mac, Linux, Chrome OS, and Android)?
No, not supported on webview.

Link to entry on the feature dashboard
https://chromestatus.com/feature/5189079788683264

[David Dabbs]

> We are still evaluating possible changes to the labeling configuration in this period between facilitated testing and third-party cookie phase-out. Further guidance will be provided in the coming milestones on any changes to labels.

Can you share changes you are evaluating, rationale?

>We expect to support labeled browser groups for some time during the third-party cookie phase-out process. In this case, the fraction of labeled browsers would increase, which was not the case in the original Intent to Experiment. We will seek approval for this in subsequent Intent to Extend Experiments, and plan to maintain a holdback group at those times.

Fractions are expected to remain as currenty publicly published on the developer blog through M129?

David

[John Delaney]

> Can you share changes you are evaluating, rationale?

The current label configuration was designed to support Chrome-facilitated testing through the period ending June 30, 2024.  We are considering ways to simplify this configuration to continue supporting developers, while also making it easier to maintain and understand.

> Fractions are expected to remain as currenty publicly published on the developer blog through M129?

We currently do not have a plan to adjust labels prior to M129, but any changes will be communicated in-advance through blink-dev and the developer blog.

[Mike Taylor]

LGTM to extend from 127 to 129 inclusive.

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[John Delaney]

We wanted to clarify that the above extension also includes sending the Cookie-Deprecation label headers during the trusted bidding and trusted scoring signals fetches for Protected Audience auctions (https://github.com/WICG/turtledove/issues/946) as noted on the original I2E.

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