import { Cards, Callout, Steps } from 'nextra/components'

Feature Flags: Rollout with precision control

Feature Flags is a separately priced product add-on. It is currently only offered to those on the Enterprise Plan. See our [pricing page](https://mixpanel.com/pricing/) for more details.

Overview

Feature Flags let you control who sees a feature and when. Use them to:

Gradually roll out changes (E.g 1% → 10% → 100%)
Target cohorts, regions, platforms, or group accounts
Kill-switch risky functionality instantly
Serve variants for A/B/x tests and analyze results with Mixpanel Experiments

Flags deliver variants to users whereas Experiments measure impact with statistical rigor. Use flags to deploy and orchestrate and use experiments to decide.

Concepts & terminology

Flag Key — unique identifier for a flag used by SDKs.
Variant Assignment Key — the randomization bucket unit: distinct_id (user), device_id, or a group key like account_id.
Variants — experience labels (e.g., control, A, B).
Variant Splits — allocation across variants (e.g., 90%/10%).
Fallback Value — variant to use when an assignment is unavailable.
Sticky Variants — the same entity keeps the same variant over time.
Rollout Groups - The configuration determining which users are in the rollout. This is comprised of:
- Targeting — eligibility definition (All Users vs Cohorts; may include runtime properties).
- Rollout % — percentage of the eligible audience that receives the flag now.
Rollout % — percentage of the eligible Rollout Group that receives the flag now.
Runtime Properties — request-time attributes (e.g., URL path, app version) used to target immediately.
Assignment vs Exposure — assignment is deciding the variant; exposure is when your app uses that variant to render.
Feature Flag API Request - is a call made to a feature flag API to retrieve the current state or configuration of one or more feature flags. This request allows an application to dynamically determine which features should be active for a user
Context - key value pairs mapping variant assignment keys to user values for variant assignment

Types of Feature Flags

We support the following types of Flags

Feature Gate : Toggle a feature on or off for targeted users or all users. Useful for phased or controlled rollout.
Experiment : Deliver different variant experiences (e.g., layouts, flows, pricing) to a targeted group of users. Enables measuring and analyzing impact.
[Coming Soon] Dynamic Config : Configure features with flexible key-value pairs instead of just on/off. It lets you:
- Pass JSON payloads (e.g., {"cta_text": "Buy now", "discount": 20}) to customize behavior or UI dynamically
- Update values instantly without redeploying code

Targeting & Identity Management

### Variant Assignment Key

This is the randomization bucket unit: distinct_id (user), device_id, or a group key like account_id.

How to choose the right key?

User distinct_id — best for logged-in experiences across device; a user sees a consistent experience across various sessions and devices
Device device_id — best for pre-auth or acquisition flows; a device keeps a consistent variant between pre-auth and post-auth experiences.
Group group_id — target by account/org using a group key (e.g., account_id). Values for group keys will need to be supplied to the Mixpanel feature flag SDK through the context parameter

Variants Management

Variants are served / allocated around the variant assignment key

Variant management includes 3 concepts -

Variants are the experiences to serve. (e.g., control, A, B).
Variant split % is the allocation across the variants.
- For example, 10% of users in variant A, and 90% in variant B.
Sticky Variants ensures continuity in the variant experience served
- If a user is assigned to a sticky variant B, regardless of how variant splits, rollout percentage, or cohort memberships change in the future, the user will continue to see the variant B.

Control variant by is always set to non-sticky. This is to ensure this is the only group of users that can move up to other variants if allocation of other variants is increased.

Rollout Groups

Feature flags may consist of one or more rollout groups. Users are evaluated against each rollout group in order until one is found that the user qualifies for.

You can target 'All Users', or optionally target rollout of your feature flags to subsets of your user base rather than to all your users with Cohorts. These are dynamic audiences of Mixpanel users based on user behavior or properties. Use these to target feature flags to specific subsets of your user base. For example, target only users who did 5 purchases in the last week.

- Cohorts used in feature flag targeting refresh on a periodic cadence (~every 2 hours). So once a user qualifies for a cohort, it can take up to 2 hours before they see a desired experience. - If you want users to continue seeing the same variant even if they disqualify from the cohort in the future, couple this with **Sticky Variants.** This will ensure a user continues to see the new experience until the flag is turned off.

Runtime Targeting

This method enables targeting users immediately based on device or platform properties. For example, only users who are on Android devices and in the UK.

When building a cohort, if you add a filter, navigate to + Create New, you'll be able to add a new runtime property filter.
Runtime properties (e.g., platform, path, country) should be passed by the SDK at request time for immediate, per-request decisions.

Rollout Percentage

This is the percentage of the requests that should be targeted, according to the Variant Assignment Key.

Example: If we want to rollout to 50% of Active Users cohort, and 10% to Dormant User Cohort, we would create

2 rollout groups : Rollout Group 1 - Active Users, Rollout Group 2 - Dormant Users
Rollout percentage will be applied to each Rollout Group : 50% and 10% respectively

Variant allocation happens within the roll-out group.

Example: Building on the same example above, variant allocation is 50-50 for A/B.

Rollout Group 1 - Active users will see - 25% users in A (50% of 50%); 5% users in B (50% of 50%)
Rollout Group 2 - Dormant users will see - 5% users in A (50% of 10%); 5% users in B (50% of 10%)

Frequently Asked Questions

1. How do Data Views affect feature flags?

Feature flags are scoped to data views. If targeting your flag to specific user cohorts, only end users included in the data view where the flag is created, will be targeted. Only users with access to a data-view and can view and edit the flag

2. Can I target a cohort, but also include run-time targeting like device or url path?

Yes. You can couple run-time targeting with general cohorts. It works with an and condition across the 2 groups.

3. Why is control variant always non-sticky? I want all my variants to be sticky

Control variant is set to always be non-sticky to ensure this is the only group of users that can move up to other variants if allocation of other variants is increased. This is to avoid users moving from non-control variants.
NOTE: If you do want all users to be sticky and do not anticipate needing to change the variant allocation, mark control variant as 0%, and allocate all the 100% to the other variants. This is recommended for use-cases where you have no default or control experience, and are testing a brand new experience with 2+ variants

4. How do we avoid overlapping target audiences across 2 different feature flags?

Let's say we have 2 features: feature A and feature B, and we want these to be non-overlapping in audience targeting. In the feature flag B page, in the target audience -

Create Rollout Group 1: any user who was exposed to feature flag A
- Variant served: control 100% (no new experience, revert to default)
- Rollout % : 100%
Create Rollout Group 2: All users, or any specific users you want for flag B

5. Are there any limits to variants or rollout group?

Yes, today you can have a maximum of 5 variants per flag, and a maximum of 5 rollout groups per flag

Governance, permissions & audit trail

We recommend establishing light-weight controls without slowing teams.

Permissions

Project Role — you need to have at least an “analyst” role to create and edit feature flags. “Consumer” roles can only view feature flags.
- [coming soon] Overall Feature Flag permissions - this setting allows you to give users or teams access to all feature flags. It overrides the permissions set at a per-flag level. For example, you might want your ops-lead team to have edit access to all flags for emergencies.
Feature Flag Permissions — You can manage share settings per flag.. Only editors for a flag will have access to modify a flag generally.

Audit Trail

This shows the history of changes related to the flag. This allows you to know the change history (who, what, when) of all the updates.

QA Testers

This section allows you to whitelist users who will receive the experience, vs rolling out more broadly. You can select users based on the $email user profile property. Once selected, you can specify which experience you would like each user to get.

Testing Environment

Use separate Mixpanel projects, which are connected to your different environments, to reduce risk and promote safety. You might have just 1 or 2 of these, which is also fine -

Dev Project — rapid iteration; permissive targeting
Staging Project — mirrors prod cohorts; dry runs for promotion
Prod Project — customer-facing

Recommended workflow:

Create the flag in dev with a consistent Flag Key. Validate eligibility, variants, etc.
Create the same flag in staging. Use the same Flag Key. QA Test in this mode
Lastly, create the same flag in prod. Use the same Flag Key. Ensure the right edit permissions are provided, and the right rollout % is set.

[Coming soon]: Ability to push a flag from Dev or Staging project to Prod project in one click.

Performance, Reliability & security

Privacy

EU & IN projects must initialize the SDK’s with the correct api host endpoints for their regions.
You should only send the context/runtime properties you need; avoid sensitive PII.

Regions

Keep traffic within region by using the correct project & API hosts.

Reliability

Mixpanel analytics downtime will result in suspended cohort membership refreshes, though feature flag variants will continue to be served.

When using sticky variants, the last available variant per user will be served.
In case of Feature flagging service downtime, your fallback variant will be served by the SDKs.

Performance

The latency of Feature flags API responses is usually on the order of milliseconds. NOTE: Cohort membership is refreshed every 2 hours when targeting anything aside from 'All Users' or 'Run Time Properties'. Therefore, new users entering cohorts may not be reflected in Feature flags API responses for up to that 2 hour period.

Implementation

Feature Flagging is supported on three client-side SDK's: Web, iOS, and Android and currently in "Beta" on one server-side SDK, python.

See our developer guides on implementing feature flags on these platforms below:

Coming soon: React Native, Java, Ruby, Node.js, Go

If you'd like to see Feature Flags availability in other SDKs, please [reach out to the Support team](https://mixpanel.com/get-support).

Other Implementation Methods

We use a CDP in our company. How do we use Mixpanel Feature Flags with our CDP? You have two options -

Option 1: Use Mixpanel sdk for purely feature flagging assignment and exposure event $experiment_started
Option 2: Use mixpanel sdk for only feature flagging assignment, not exposure event
- When you initialize the mixpanel feature flag SDK, configure it to not track any $experiment_started events directly to Mixpanel.
- This way you use the mixpanel SDK to serve the feature flags, but when an end-user sees exposure, they manually use their existing method of tracking events through their CDP to mixpanel to track the $experiment_started event

Feature Flagging Pricing FAQ

Feature Flags is a separately priced product offered to organizations on the Enterprise Plan. Please [contact us](https://mixpanel.com/contact-us/sales/) for more details.

Pricing Unit: Feature Flags are priced based on Feature Flag API Requests, and number of 'active' feature flags at any time

1. What is a Feature Flag API Request?

A feature flag API request is a call made by your application to a Feature Flag system’s API to determine which all features should be enabled or disabled, or which variant should be served to a user. All the active flags in the system are evaluated as part of this API request.

2. How can I estimate Feature Flag API requests?

In general, you can expect every user session to have 1 API request. When the session starts, all the flags for the user are fetched in the single API request. So monthly API requests is at minimum equivalent to the total user sessions that month. Few notes:

If you have multiple sdk inits each session, that would increase the count of API requests in a session
Considering above, general rule of thumb: would consider API requests to be 1.5 x User Sessions considering implementation challenges, or multiple sdk inits in a session

3. How do I estimate API requests if implementing via server side sdk?

If you are using server side sdk, with only local evaluation: your API requests depend on a) how many server instances you have and b) how frequently you poll your servers
If you are using server side sdk, but with remote evaluation or leveraging cohorts: your API request estimation is similar to client-side sdk requests laid our above

4. What happens if I go over my purchased Feature Flag API Request bucket?

You can continue using Mixpanel Feature Flags, but you will be charged a higher rate for the overages.

5. Is there any limit on number of feature flags per API request?

Yes, there is a limit depending on the plan you purchase. You can choose from 3 plans: to have upto 50, 200 or 1000 'active flags' per API request.

Once you reach this limit, no more flags will will be fetched as part of the API request until you disable some others or upgrade your plan
Active flags are flags which are marked 'Enabled'. Only these flags are counted under the 'active flag' limit
If you are on the 50 active flag limit, the first 50 flags based on the 'start' date are fetched

6. Do I get double charged if I create the same feature flag across projects?

No. We charge based on active 'feature flag keys'. If the same flag-key is used across projects, it will be charged only once.

7. How can I monitor my account’s Feature Flag API requests consumption?

You can see your feature flag usage by going to Organization settings > Plan Details & Billing.

8. If I purchase the feature flag add-on, do I still need to purchase the experimentation add-on as well?

Yes. Both these are separate add-ons to ensure we're compatible with your tech stack. So, if you are also looking to analyze experiments, please check our [experimentation offering.] (https://docs.mixpanel.com/docs/experiments)

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!