> ## 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.

# Get test cohort

> Read a single test cohort by ID

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

Returns the full test cohort resource, including its targeting `definition`.

## Request

<CodeGroup>
  ```bash curl theme={null}
  curl https://api.interchange.io/api/v2/buyer/advertisers/12345/test-cohorts/cohort_abc123 \
    -H "Authorization: Bearer $SCOPE3_API_KEY"
  ```
</CodeGroup>

## Parameters

| Field          | Type   | Required | Notes                                  |
| -------------- | ------ | -------- | -------------------------------------- |
| `advertiserId` | string | Yes      | Path parameter — the owning advertiser |
| `cohortId`     | string | Yes      | Path parameter — the cohort ID         |

## Response

```json theme={null}
{
  "id": "cohort_abc123",
  "advertiserId": "12345",
  "name": "West Coast Treatment Group",
  "description": "Users in CA, OR, WA receiving full ad exposure",
  "cohortType": "geographic",
  "role": "TREATMENT",
  "definition": { "type": "geo_region", "regions": ["US-CA", "US-OR", "US-WA"] },
  "estimatedSize": 50000,
  "isActive": true,
  "createdAt": "2026-01-15T10:30:00Z",
  "updatedAt": "2026-01-20T14:45:00Z"
}
```

## Errors

* `404 NOT_FOUND` — `cohortId` (or `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="Update test cohort" href="/v2/buyer/measurement/tasks/update-test-cohort" icon="pen">
    Change definition or role
  </Card>
</CardGroup>