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Optimizely Knowledge Base

Launch features with feature rollouts

Relevant products:
  • Optimizely X Full Stack

  • Mitigate risk with feature rollouts
  • Control how much traffic to your site sees a feature
  • Gradually expose winning variations of your feature to visitors

A feature rollout is the process of exposing a new feature to specific visitors in a controlled fashion. Feature rollouts (“rollouts”) allow you to specify the percentage of traffic for which a feature is enabled and apply audiences to target a group of visitors based on attributes.

Rollouts help you mitigate risk. Rollouts for new features default to OFF with 0% of traffic allocated. You can adjust rollout as needed as you iterate on and refine your feature. For example, if you want to be sure that a new feature doesn’t degrade the visitor experience, start by launching the feature to a small percentage of visitors.

Rollouts also let you launch winning variations that you identify through experimentation. For example, if you find a winning variation when running a feature test, use a feature rollout to gradually expose the winning variation to your visitors in a controlled fashion.

Here’s how to launch a feature rollout, with step-by-step instructions below:


  1. Navigate to Features and select the name of the feature you want to roll out.

  2. Under Rollout, set the Feature toggle to ON and use the slider to specify traffic allocation.
    If you prefer, type the traffic allocation directly in the Traffic field.

  3. Click Save.

After defining or changing a rollout, you must click Save to confirm your changes. If you enable a rollout for a non-zero traffic percentage, clicking Save launches the rollout.

Bucketing logic and traffic percentages in feature rollouts

Feature rollouts use the same bucketing logic to evaluate traffic allocation as in traditional Full Stack A/B tests: we combine user ID and a unique rollout ID and compute a deterministic hash that outputs a number between 0 and 10,000. If that number falls within the range specified by the feature rollout’s traffic allocation, the visitor is eligible for the feature.

If you toggle a feature rollout on for a percentage of traffic, then toggle it off, then toggle it back on, the rollout will retain the previously defined traffic percentage. This ensures that you can turn the same features back on for the same percentage of visitors. For example, imagine you roll out a feature to 1% of your site traffic, then learn that the feature is broken. You can turn off the feature, deploy a fix, then turn the feature back on. The same 1% of traffic who saw the broken feature will see the fixed feature.

Target rollouts by audience

Target feature rollouts using the same audiences you would use in a traditional Full Stack A/B test:


  1. Navigate to Features and click the feature you want to target by audience.

  2. In the Audiences section, click the names of the audiences you want to add.

  3. Click Save.

You can target more than one audience for a feature rollout. Multiple audiences are combined with the Boolean operator OR.

Manage feature rollouts

Feature tests take precedence over feature rollouts.  If there is a test and a rollout running on a feature, the test will be evaluated before the rollouts. Learn more about interaction between feature tests and feature rollouts.

The Features dashboard gives you a snapshot of what is happening to a feature at a given point in time:


  • Active Experiments: lists all active (running or paused) feature tests for each feature.

  • Rollout: shows the traffic allocation if a rollout is currently running for the feature (or OFF, if the feature is toggled off).

  • Created: date the feature was created

  • Modified: date the feature or rollout was last modified

To archive a feature, click … and select Archive: