demo · v134

Aggregatable Report Limit Lifted

When a trigger registration sets trigger_context_id, the per-source aggregatable report cap (previously 20) no longer applies. Each conversion can spawn its own report. Use the probe below to build registrations and compare the report eligibility the backend returns.

Heads up Attribution Reporting is a Privacy Sandbox API. To exercise browser registration, enable chrome://flags/#privacy-sandbox-ads-apis-override and register with attributionsrc-bearing pixels. This page calls the local trigger-registration endpoint so the response header is emitted by a server route.
probing navigator.attributionReporting...

Try it — trigger header probe

Set the number of conversions and toggle whether each trigger carries a trigger_context_id. The bars show how many aggregatable reports are eligible under the new and old rules.

conversions 42
trigger_context_id mode
waiting for backend route…

pre-134 (cap = 20)

v134+ (no cap when ctx_id set)

backend-emitted header

waiting for fetch…

The cap lift is not a looser privacy budget. Setting trigger_context_id changes how many aggregatable reports may be generated from one source; contribution budgeting, aggregation, and noise still govern what can be learned from those reports.

The code

// reporting origin sends, on a trigger pixel:
Attribution-Reporting-Register-Trigger: {
  "aggregatable_trigger_data": [...],
  "aggregatable_values": {"key": 1},
  "trigger_context_id": "conv_42"   // <-- non-empty string lifts the cap
}

see also