In the PA-API, there is a 10MB limit for interest group size on devices (as per https://wicg.github.io/turtledove/#max-interest-groups-total-size-per-owner). Currently, ad-tech companies lack visibility into the frequency with which browsers reach this limit, resulting in interest group purging. This information is crucial for understanding the extent to which interest group payload optimization is necessary. We propose that Chrome implement a mechanism to surface this data, maybe along with the distribution of interest group sizes, potentially through the Private Aggregation Reporting API.

Additionally, we have a similar request to expose time-out information via the Private Aggregation API (patcg-individual-drafts/private-aggregation-api#119).