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, on the audience card and in the launch footer. For the Standard sample of 1,000 synthetic shoppers, the estimate is about 20 minutes. It's an estimate, not a guarantee — the actual time depends on the pages and the sample size you chose. A larger sample runs longer; a smaller one finishes sooner.
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, or a larger sample. 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.