Chrome advises that ad tech checks whether the relevant API is available before using it, using the approaches documented here.

However, if a user opts-out of Privacy Sandbox trials (e.g., by visiting chrome://settings/privacySandbox), the sandbox APIs still appear exposed to javascript.

This presents a challenge, particularly for FLEDGE, as significant resources and latency can be incurred when attempting call FLEDGE's runAdAuction. For example, if sellers believe FLEDGE is eligible to run, they may:

• Call out to buyers with this information, in order to fill perBuyerSignals
  • Buyers may, in turn, spend additional resources/compute in order to generate their signals
• Run additional server-side FLEDGE-specific code (e.g., to generate an AuctionConfig in preparation of the FLEDGE auction)
• Call the runAdAuction API, releasing the thread on the client and potentially incurring unbounded latency before rendering an available contextual ad (i.e., while waiting for runAdAuction to return, in competition with other tasks on the page)

In contrast, if access to an API is disabled via a permissions policy, callers can check whether the feature is blocked before calling the relevant API.

Ask:

• Ideally, Chrome would provide a ‘user has opted out of sandbox APIs’ signal, which ad tech and websites can use to know whether to run any sandbox-specific setup/function calls
• Alternatively, Chrome can more simply make the API unavailable, similar to users who are not participating in the origin trials, so that no calls against the API are possible