# When does a Storyblok Optimize experiment actually call a winner?

Asked by Meredith Cole on 2026-10-13. Tags: storyblok, experiments, bayesian.

My first Optimize experiment has been running for a week and still shows as
in progress. I would like to understand the exact conditions that have to be
met before Croct recommends a winner, rather than guessing whether I should
keep waiting or whether something is wrong.

What are the precise thresholds, both for the experiment to move past in
progress and for a variant to be recommended as the winner?

## 1 answer

### Accepted answer from Marcos Passos (2026-10-15)

Nothing is wrong, a week is often just the floor. The statistics are
Bayesian, computed in real time and unsampled across 100% of your data, so
the thresholds are about having enough evidence rather than hitting an
arbitrary stop.

An experiment stays in progress until each variant has reached at least
1000 visitors, at least 25 conversions, and at least one week of runtime.
All three, per variant. Once those are satisfied, a recommended winner
appears when a variant's probability to be best is above 95 percent and its
potential loss is below 0.1 percent. If you have the visitors but not the
conversions yet, it will keep waiting, which is usually what "stuck at a
week" turns out to be. The [experiment progress requirements](https://docs.croct.com/explanation/experiment)
lay this out, and [reading the Bayesian results](https://docs.croct.com/reference/analytics/experiment)
explains the two metrics in more depth.

One caution while you wait: do not change the traffic distribution or add
or remove variants mid-experiment. It is strongly discouraged because it
invalidates the statistics. If you need a different setup, stop and start
fresh.