> ## Documentation Index
> Fetch the complete documentation index at: https://docs-dev-docs-event-stream-action-templates.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Experiment Center

> Learn about Auth0 Experiment Center and how to create authentication flows for A/B testing.

export const ReleaseStageNotice = ({feature, stage, plans, contact, terms}) => {
  const stageTextMap = {
    "beta": "Beta",
    "ea": "Early Access"
  };
  const stageText = stageTextMap[stage] || "a product release stage";
  const prsLink = "/docs/troubleshoot/product-lifecycle/product-release-stages";
  const linkify = (text, url) => {
    return <a href={url} target="_blank" rel="noreferrer" class="link">{text}</a>;
  };
  const includeDetails = (plans, contact, terms) => {
    const hasDetails = terms || plans || contact;
    if (!hasDetails) return null;
    return <span data-as="p">
            {plans && <>This feature is available for {linkify(`${plans} plans`, "https://auth0.com/pricing")}. </>}
            {contact && "To participate, contact " + contact + ". "}
            {terms && <>By using this feature, you agree to the applicable Free Trial terms in Okta's {linkify("Master Subscription Agreement", "https://www.okta.com/legal")}.</>}
        </span>;
  };
  return <Warning>
            <span data-as="p">
                <strong>The {feature} feature is in {linkify(stageText, prsLink)}.</strong>
            </span>

            {includeDetails(plans, contact, terms)}
        </Warning>;
};

<ReleaseStageNotice feature="Auth0 Experiment Center" stage="beta" terms="true" contact="Auth0 Support" />

Auth0 Experiment Center is a native Auth0 experimentation engine. It lets you A/B test changes to your [authentication](/docs/authenticate/login/auth0-universal-login) experience and see the impact in your auth event [logs](/docs/deploy-monitor/logs).

With Experiment Center, you define your A/B test in Auth0, traffic splits deterministically, and your existing auth events come back enriched with experiment metadata so you can analyze results in your own tools.

## How it works

Experiment Center lets you run controlled A/B tests on your Auth0 authentication pipeline. Instead of deploying a change to every user at once, you expose new behavior to a controlled percentage of traffic, measure the result through enriched auth events, and promote the winner when you are ready.

Experiment Center is built around three entities:

* **Experiment**: defines how traffic is split and when the test runs.
* **Feature flag**: defines what you are testing and the possible variations.
* **Segment**: defines a set of rules to route experiments to specific variations.

<Warning>
  During Beta, Experiment Center runs on development tenants only. Production tenants are not supported.
</Warning>

## Experiment

An experiment is a measurement wrapper around a feature flag. It defines:

* Which feature flag is being tested
* How traffic is allocated across variations
* When the test is running

Each experiment references exactly one feature flag.

### Experiment lifecycle

Experiments have five states:

| Status      | Meaning                                                                                      |
| ----------- | -------------------------------------------------------------------------------------------- |
| `draft`     | Created but not running. Safe to test using query parameter overrides.                       |
| `active`    | Running. Variant assignment and context injection are live for all auth transactions.        |
| `paused`    | Temporarily suspended. No new assignments. In-flight sessions keep their assigned variation. |
| `completed` | Concluded. No new assignments. Configuration retained for reference during manual promotion. |
| `archived`  | Soft-deleted. Hidden from default list views. Analytics data retained.                       |

### Allocation strategies

An experiment uses one of two allocation strategies:

**Percentage-based:** Traffic is split across variations by weight. All weights must sum to 100. A weight of 0 is valid (the variation is in the experiment definition but receives no traffic).

**Segment-based (targeted):** Traffic is routed to variations based on segment membership. Segments are evaluated in priority order. The first matching segment wins. If no segment matches, the `is_fallback` allocation receives the request.

To learn more about the experiment entity, read [Entities Details](/docs/customize/experiment-center/entities#experiment).

### Experiment context

When an experiment is active and a variation is assigned, Experiment Center injects an `ExperimentContext` object into your runtime surfaces.

[ACUL](/docs/customize/login-pages/advanced-customizations#advanced-customizations-for-universal-login-acul) screens receive it only when you opt the screen in via `context_configuration`.
To learn more, read [ACUL integration guide](/docs/customize/experiment-center/integrations/acul-integration-guide).

[Actions](/docs/customize/actions/actions-overview) and [page templates](/docs/customize/login-pages/universal-login/customize-templates#customize-universal-login-page-templates) receive it automatically whenever an experiment is active. The object shape:

```typescript theme={null}
{
  experiment_id: string;   // The active experiment ID
  variation_id: string;    // The assigned variation ID
  config: {                // Merged configuration (baseline + overrides)
    [paramName]: { value: unknown }
  };
  is_control: boolean;     // True if this is the control variation
}
```

The `config` field contains the complete merged configuration for the assigned variation. Every parameter defined on the feature flag always has a value. You do not need to write fallback logic.

### Assignment

An assignment is how a user gets routed to a specific variation during an auth transaction. Assignments are deterministic and sticky: the same user consistently sees the same variation for the same experiment on the same device, so their experience stays stable across logins.

* **Percentage allocation** splits traffic across variations by weight. A given subject is consistently assigned to the same variation.
* **Segment allocation** evaluates the request's properties against your segment rules in priority order. The first matching segment determines the variation, and a request that matches the same segment always resolves to the same variation.

Assignment results are recorded in your tenant logs under `details.experiment`; they are not exposed through a separate API.

To learn more about the assignment entity, read [Entities Details](/docs/customize/experiment-center/entities#assignment).

## Feature flag

A feature flag is the control unit for what is being tested. It contains:

* A **baseline configuration**: typed parameters and their default values
* One or more **variations**: alternative configurations that differ from the baseline

Feature flags are tenant-scoped and reusable. The same flag can be referenced by multiple experiments over time (for example, a Q1 test and a Q2 refinement on the same feature).

### Feature flag lifecycle

Feature flags have a stored lifecycle with three states:

| Status     | Meaning                                                                               |
| ---------- | ------------------------------------------------------------------------------------- |
| `draft`    | Created but not yet active. Cannot be referenced by an active experiment.             |
| `active`   | Ready for use. Required before any experiment that references this flag can activate. |
| `archived` | Terminal. No new experiments can reference this flag. Create a new flag if needed.    |

To learn more about the feature flag entity, read [Entities Details](/docs/customize/experiment-center/entities#feature-flag).

### Variation

A variation is one version of the experience defined within a feature flag. It specifies which configuration parameters differ from the baseline, and by how much.

* The **control variation** is the baseline; it has empty overrides (no parameters changed from the flag's defaults).
* **Treatment variations** each specify one or more parameter overrides.

Variations do not carry an `is_control` marker. Whether a variation is the statistical control for a given experiment is set on the allocation, not the variation. The same variation can be the control in one experiment and a treatment in another.

To learn more about the variation entity, read [Entities Details](/docs/customize/experiment-center/entities#variation).

## Segment

A segment is a named group of authentication requests that match a set of rules. You use segments in targeted allocation experiments to route specific traffic cohorts to specific variations.

Segments are tenant-scoped and reusable across experiments.

To learn more about the segment entity, read [Entities Details](/docs/customize/experiment-center/entities#segment).

## Limitations

The following limitations apply during Beta:

* **One active experiment per tenant.** You can have many experiments in `draft`, `paused`, or `completed` states, but only one can be `active` at a time.
* **Structured parameters only.** Feature flag parameters use the key/type/value structure.
* **Three Actions triggers.** Experiment context is available in [`post_login`](/docs/customize/actions/explore-triggers/signup-and-login-triggers/login-trigger), [`pre_user_registration`](/docs/customize/actions/explore-triggers/signup-and-login-triggers/pre-user-registration-trigger), and [`post_user_registration`](/docs/customize/actions/explore-triggers/signup-and-login-triggers/post-user-registration-trigger).
* **Test traffic only.** Beta runs on development tenants with traffic you generate. Production end-user data does not flow through Beta.
* **Manual promotion.** When an experiment completes, you apply the winning variation's configuration to your tenant manually.

## Learn more

Read **[Entities Details](/docs/customize/experiment-center/entities)** to learn about Experiment Center entities and properties.

Read **[Experiment Center Quickstart](/docs/customize/experiment-center/quickstart)** to learn how to create a flag, activate an experiment, and observe enriched log events end to end.