STTV

STTV is the acronym for Start Time To Variant, representing the duration between page load initiation and the moment an A/B test variant becomes visible to users.

Meaning & Context

STTV is a key performance indicator for evaluating A/B testing platform efficiency, particularly for client-side implementations. It encompasses the time required for test script loading, variant assignment logic execution, and DOM manipulation to display the correct experience. Industry best practice targets STTV under 100-200 milliseconds to minimize user experience impact.

Why It Matters

Monitoring STTV helps optimization teams identify when their testing infrastructure itself becomes a performance bottleneck. Excessive STTV creates cumulative layout shift, harms Core Web Vitals scores, and can suppress conversion rates across all test variants. Teams often use STTV as a deciding factor when choosing between client-side, server-side, or edge-based testing architectures.

Example

An analytics dashboard shows that mobile users experience an average STTV of 1.2 seconds while desktop users see only 400ms, prompting the team to implement asynchronous loading specifically for mobile variants to reduce the performance gap.