> ## Documentation Index
> Fetch the complete documentation index at: https://docs.interchange.io/llms.txt
> Use this file to discover all available pages before exploring further.

# List test cohorts

> List the incrementality test cohorts defined for an advertiser

`GET /api/v2/buyer/advertisers/{advertiserId}/test-cohorts`

Lists test cohorts for an advertiser — the treatment, control, and observation arms used in incrementality tests. Filter by role and active status.

## Request

<CodeGroup>
  ```bash curl theme={null}
  curl "https://api.interchange.io/api/v2/buyer/advertisers/12345/test-cohorts?role=TREATMENT&isActive=true&take=50&skip=0" \
    -H "Authorization: Bearer $SCOPE3_API_KEY"
  ```
</CodeGroup>

## Parameters

| Field          | Type    | Required | Notes                                    |
| -------------- | ------- | -------- | ---------------------------------------- |
| `advertiserId` | string  | Yes      | Path parameter — the owning advertiser   |
| `role`         | enum    | No       | `TREATMENT`, `CONTROL`, or `OBSERVATION` |
| `isActive`     | boolean | No       | Filter by active status                  |
| `take`         | integer | No       | Page size, max 250 (default 50)          |
| `skip`         | integer | No       | Offset for pagination (default 0)        |

## Response

```json theme={null}
{
  "cohorts": [
    {
      "id": "cohort_abc123",
      "advertiserId": "12345",
      "name": "West Coast Treatment Group",
      "cohortType": "geographic",
      "role": "TREATMENT",
      "estimatedSize": 50000,
      "isActive": true,
      "createdAt": "2026-01-15T10:30:00Z",
      "updatedAt": "2026-01-20T14:45:00Z"
    }
  ],
  "total": 6
}
```

Returns compact cohort summaries plus a `total` count matching the query. Summaries omit `definition` and `description` — use [Get test cohort](/v2/buyer/measurement/tasks/get-test-cohort) for the full resource. This endpoint is offset-paginated; see [Pagination](/v2/reference/pagination) for the `meta.pagination` envelope fields.

## Errors

* `404 NOT_FOUND` — `advertiserId` does not exist or is not visible to the authenticated account.

See [Errors](/v2/reference/errors) for the full error contract.

## Related

<CardGroup cols={2}>
  <Card title="Measurement tasks" href="/v2/buyer/measurement/tasks" icon="list-check">
    All measurement operations
  </Card>

  <Card title="Measurement overview" href="/v2/guides/measurement-incrementality" icon="chart-line">
    Pipeline, belief state, and concepts
  </Card>

  <Card title="Create test cohort" href="/v2/buyer/measurement/tasks/create-test-cohort" icon="plus">
    Define a new arm
  </Card>
</CardGroup>