Experiment lifecycle and auto-stop¶
An experiment warms up, runs while synthetic shoppers fill the floor, then completes and files a verdict. This page explains what happens at each phase, how long a run takes, and how auto-stop decides when to end it.
The phases of a run¶
When you click Launch experiment, the run starts and moves through these phases on the experiment page.
- Warming up. Squoosh reserves the synthetic shoppers and prepares both versions of your page — Control page (A) and Variant page (B). No shoppers are on the floor yet. While the run is in this phase, the stop control reads Cancel launch.
- Shoppers entering. The first synthetic shoppers begin to shop both versions, and the floor starts to populate. The stop control changes to Stop.
- Live. The full run is underway. The shopper floor fills in as more shoppers finish, alongside a combined funnel and what individual shoppers did and said. The status reads Live.
- Completed. Every shopper has finished both versions, Squoosh files the verdict, and the status reads Completed.
What you see while a run is Live¶
While a run is Live, the page shows the shopper floor, the combined funnel across both versions, and feedback from individual shoppers. It does not show a winner, a lift, or a confidence figure.
Those numbers are a finish-line reveal. They appear only once the run completes, so a partial result can't mislead you mid-run. For how to read them after the run, see How Squoosh decides a winner and Reading lift and confidence.
How long a run takes¶
Squoosh shows an estimated time before you launch, in the Review step and the launch footer. For an A/B test, the estimate is about 10 minutes. It's an estimate, not a guarantee — the actual time depends on the pages and how quickly a clear winner emerges.
A run can also end before its estimated time if a clear winner emerges. That's auto-stop.
Auto-stop¶
Auto-stop is always on. A run ends early once a winner holds at 80% confidence, and never before 40% of the sample finishes. You don't configure it, and there's no toggle to turn it off.
The two rules work together:
- The 80% confidence bar is the point at which Squoosh is sure enough to call a winner. Squoosh decides winners at 80% confidence rather than the 95% a traditional A/B tool waits for. See How Squoosh decides a winner.
- The 40% completion floor guarantees enough of the sample finishes for the result to be trustworthy, so a few early shoppers can't end the run on a fluke.
The practical effect: a clear result comes back sooner, and a close one runs longer. A test where one version pulls decisively ahead can stop not long after the floor clears. A test where the two versions stay near each other runs out the full sample looking for separation.
A Conversion Report shares this lifecycle but stops when its funnel read is stable rather than at a confidence bar.
How a run ends¶
Every run reaches one of these final states. The state shows as the status on the experiment page and in the experiments list.
| Status | What it means | What to do |
|---|---|---|
| Completed | The run finished and Squoosh filed a verdict. | Read the verdict: ship the variant, keep the original, or re-test if it was too close. |
| Undecided | The run finished, but the two versions never separated enough to call a winner. | Re-test with a sharper change between A and B. This is not a failure. |
| Terminated | You stopped the run before it finished. | Launch a new experiment when you're ready. |
A run you haven't launched yet shows as Draft.
Stopping a run yourself¶
You can end a run early from the top of the experiment page:
- Before any shoppers are live, the control reads Cancel launch.
- Once the run is Live, it reads Stop.
Either way, the run ends in the Terminated state. It does not file a verdict.
Note
A run always reaches a final state. Squoosh recovers a run that stalls so an experiment never hangs. If a single shopper can't reach a decision, that shopper is recorded as undecided rather than failing the run.