How to get active users from the GA4 Data API

The endpoint

GA4 reporting is one POST to the Data API.

curl -s -X POST \
  'https://analyticsdata.googleapis.com/v1beta/properties/123456789:runReport' \
  -H "Authorization: Bearer $ACCESS_TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{
    "dateRanges": [{ "startDate": "2026-10-01", "endDate": "2026-10-07" }],
    "dimensions": [{ "name": "date" }],
    "metrics": [{ "name": "activeUsers" }]
  }'

The property id is numeric, and it goes in the URL path. It is not the measurement id beginning with G-, which is the one in your tracking snippet. Mixing them up returns a 403 that reads like a permissions problem.

The metric names changed

If you are porting anything from Universal Analytics, the vocabulary moved.

screenPageViews is the one that catches people. There is no pageViews in GA4: the name folds app screens and web pages into one metric, because GA4 treats both as the same kind of thing.

A metric name GA4 does not know returns a 400 naming the field, which is at least a clear failure.

The response, and where the total is

{
  "dimensionHeaders": [{ "name": "date" }],
  "metricHeaders": [{ "name": "activeUsers", "type": "TYPE_INTEGER" }],
  "rows": [{ "dimensionValues": [{ "value": "20261001" }], "metricValues": [{ "value": "120" }] }],
  "rowCount": 7
}

Values are strings, including integers. "120", not 120. Summing them without converting concatenates, which produces an absurd number rather than a subtly wrong one, so at least it fails loudly.

Dates come back as YYYYMMDD with no separators.

Do not sum the rows

This is the central thing. Summing activeUsers across seven daily rows does not give you weekly active users. Each row is de-duplicated within its own day, and a person active on three days appears in three rows.

For the de-duplicated total, ask for it:

{
  "dateRanges": [{ "startDate": "2026-10-01", "endDate": "2026-10-07" }],
  "metrics": [{ "name": "activeUsers" }],
  "metricAggregations": ["TOTAL"]
}

The result arrives in totals, separate from rows, and it is correctly de-duplicated across the window. Or run the query with no date dimension at all, which gives you a single row that means the same thing.

Either way, the headline and the chart are two requests or one request with aggregations, and they will not match. That is right.

Data is sampled and thresholded

Two caveats worth carrying with any GA4 figure.

Sampling. Large properties with complex queries get sampled results, and the response says so. Check for it rather than assuming.

Thresholding. GA4 withholds rows with very few users to protect identity, especially when demographics are involved. So a breakdown can add up to less than its total, and a missing row is not a zero.

Authentication

OAuth with https://www.googleapis.com/auth/analytics.readonly, or a service account added as a viewer on the property. The service account route is better for anything unattended, because an OAuth refresh token is one revocation away from a silent outage.

Or read it off the notch

Notch Metrics calls runReport and shows GA4 active users, new users, sessions and page views in the MacBook notch, with the headline de-duplicated over the window and the chart per day, which the page explains rather than leaving you to notice.

Everything Google Analytics reports, or download Notch Metrics.