Layout A/B testing: where to run it post-Optimize

Layout A/B testing: where to run it post-Optimize

What it does: splits traffic between two ad layouts to measure RPM, not just CTR. Google Optimize is dead, so the question is what replaced it.

Setup effort: 3/5. Options: GrowthBook (free, self-host, server-side flags), VWO, or your ad manager's native split (Ezoic/Mediavine bake it in).

RPM lift seen: the test itself adds nothing — but finding a winning layout is routinely +10 to +25%.

Pros
— Server-side flags (GrowthBook) avoid the CLS flicker client-side tools cause
— Ad-manager native tests use real RPM as the metric, not a proxy

Cons
— Client-side tools repaint the layout = CLS penalty that can erase the win
— Tiny sites never reach significance on RPM (high variance)

Verdict: use your ad manager's built-in test if it has one; else GrowthBook server-side. Lift: ★★★★☆ — Risk: ★★☆☆☆
Best for: 100k+ pageviews/mo. Skip A/B entirely under 30k — you'll chase noise.