Intent to Extend Experiment: Privacy Sandbox Ads APIs

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John Delaney

Apr 12, 2023, 5:44:47 PM4/12/23
to blink-dev

We would like to extend the origin trial for all of the Privacy Sandbox Ads APIs including: Topics, FLEDGE, Private Aggregation, Fenced Frames, Attribution Reporting, and Shared Storage.

We are sending a single intent for the extension because the rationale is shared among the APIs.

Contact emails,,,

Attribution Reporting: and
Fenced Frames:
Shared Storage:
Private Aggregation:
Topics API:

A collection of APIs to facilitate advertising: Attribution Reporting, Fenced Frames, FLEDGE, Private Aggregation, Shared Storage and Topics.
Link to “Intent to Experiment” blink-dev discussion
Attribution Reporting:
Fenced Frames:
Private Aggregation:
Shared Storage:
Topics API:

Unified OT Thread:
Goals for experimentation

Experimental timeline
We'd like to extend the origin trial for 3 additional milestones, with the extension starting in 113 continuing through Chrome 115. The experiment is therefore running from Chrome 101 through 115. We previously requested an extension from Chrome 110 - 113 here.

Any risks when the experiment finishes?
The unified origin trial is only available for a subset of Chrome users, and requires developers to perform feature detection to use the APIs.

Reason this experiment is being extended
We received feedback from developers resulting in the need for continued testing and addressing several points of feedback that required changes to the APIs. The extension will allow the ecosystem more time in stable channels to continue their experiments. We additionally added individual isolated experiments for each of the Privacy Sandbox APIs, an extension will allow us to understand individual metrics outside of our existing unified experiment

These improvements include, but are not limited, to the following:

Attribution Reporting
  • Various bug fixes & utility improvements
  • Test cross app and web measurement
  • Additional debugging capabilities including source success debug reports

Fenced Frames

  • Improve latency (e.g. parallelization of FLEDGE auction support, more timeout support, more latency reporting)
  • Origin Trial Support (e.g. better integration with Private Aggregation API, k-anonymity testing, misc features)

Private Aggregation (OT started in M107)
  • Adding support for a “context ID” to support report verification within Shared Storage worklets

Shared Storage SelectURL
  • Replaced k-anon requirement with lower entropy limits during initial phase
  • Would like to have feedback from additional testers.

  • General utility improvements (filtering is less restrictive without loss of privacy)
  • Performance optimizations (topics can be sent via headers in fetch and subframe navigation requests rather than creating an iframe and calling javascript)

Feedback from the ecosystem will continue to influence the evolution of the APIs.

Ongoing technical constraints
Please see each API's initial Intent to Experiment.

Will this feature be supported on all five Blink platforms supported by Origin Trials (Windows, Mac, Linux, Chrome OS, and Android)?
Please see each API's initial Intent to Experiment.

Link to entry on the feature dashboard
Attribution Reporting:
Fenced Frames:
Private Aggregation:
Shared Storage:

Unified Feature Dashboard:

Mike Taylor

Apr 13, 2023, 11:04:02 AM4/13/23
to John Delaney, blink-dev

Hi John,

Could you comment on any additional progress made in the 5 required areas for OT extensions (see


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John Delaney

Apr 14, 2023, 3:22:17 PM4/14/23
to Mike Taylor, blink-dev

Hi Mike,

Happy to give an update on each of these points:

Each API is continuing to make progress on draft specs. All early specifications have been published and each API is currently working on iterating on more recent changes based on feedback.

TAG review requests have been made for each of the API's, except for Private Aggregation which is a work in progress.

We are currently looking at re-filing / updating these requests to include recent changes, as some of these requests were made some time ago. requests are ongoing and are expected to finish in the next couple of weeks. We have already started receiving feedback on some APIs.

WPT tests are ongoing, many are completed with sufficient coverage. Private Aggregation has not begun yet.

If you have questions on specific areas here, let me know and I can provide any additional details/context.


Yoav Weiss

Apr 19, 2023, 3:56:58 AM4/19/23
to John Delaney, Mike Taylor, blink-dev
LGTM to extend experimentation M113-M115 (inclusive)

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