When running an experiment, track each user's [exposure](/docs/feature-experiment/under-the-hood/event-tracking#exposure-events) to your feature flag's variant experience. Without exposure tracking, results aren't reliable.

{% callout type="note" %}
Exposure tracking is optional for feature flags that don't require analysis.
{% /callout %}

## Analytics REST API

In this example, the [Analytics REST API v2.0](/docs/apis/analytics/http-v2) sends an [exposure event](/docs/feature-experiment/under-the-hood/event-tracking#exposure-events) to Amplitude with `curl`.

{% api-tester type="exposure" / %}

When the request succeeds, a user appears in the Exposures chart in Amplitude Experiment.

The flag is now active in your deployment, and your experiment evaluated a user and served them the variant.

## SDKs

As with fetching variants, you can simplify exposure tracking using a client-side [Experiment SDK](/docs/sdks/experiment-sdks) in your app. Client-side Amplitude Experiment SDKs [automatically track exposures](/docs/feature-experiment/under-the-hood/event-tracking#automatic-exposure-tracking) through your installed analytics SDK whenever the Experiment SDK accesses a variant from the variant store.