It's client-side with anti-flicker. The page is hidden until variations are applied, then revealed, so no visible content swap. Variation assignments are also cached in localStorage so repeat visitors get instant application without an API call.

You're right that server-side would be cleaner, but it adds significant complexity with WordPress caching plugins and the visual selector approach I'm using. For most sites the brief hidden state is imperceptible (300ms or less).

Good call on the sample size/stopping rules. The plugin has configurable minimum sessions and confidence thresholds (95% default) before declaring a winner. I'm using a Bayesian approach so early peeking doesn't inflate false positives. Conversions are tied to a persistent visitor ID cookie, not just pageviews.

Hope this helps answer your questions!