Staged rollouts

A staged, percentage-based rollout is a special case of an A/B test with only one dimension and one arm.
To create a staged rollout, insert a "Test / ML" expression in your flag logic. Create a new "split" from the split dropdown and add a single arm with the percentage of traffic you want to roll out to. Save the split, then in your flag logic, enable your feature for that arm and disable it for the "Default" arm.