We Measured AI Code Drift Across 5 Tools and 210 Components. Frequency Alone Lied to Us.
Empirical research from ReWeaver AI. 42 identical prompts, across 5 tools and 8 production dimensions, compared to human baseline. One metric that changes how you see drift. Everyone knows AI-generated code has quality issues. What’s less understood is that the way most teams measure those issues — by how often they occur — systematically understates the risk. We ran a controlled study to find out how badly. The answer surprised us, particularly in one dimension. What We Did We gave five leading AI coding tools (Cursor, Claude Code, Lovable, Figma Make, and VS Code with Copilot) 42 identical prompts: realistic single-component builds — buttons, forms, dashboards, navs, modals, auth surfaces. We scanned every output with ReWeaver, our deterministic drift-detection engine, across eight production readiness dimensions: User Experience Security & Privacy Accessibility Design Consistency Reliability Maintainability Architecture Testability We also scanned six human-authored open-source repositories as a reference baseline. For each dimension, we calculated two things: Drift frequency — the percentage of lines containing at least one drift occurrence. Counts what went wrong. Production Drift Ratio (PDR) . The PDR is a metric that weights frequency by estimated remediation cost on a 0–1 scale. A PDR of 0.30 is roughly 45 minutes of cleanup per component; 0.70 is about 2.5 hours. The Finding That Stopped Us In Security & Privacy , AI tools produced 3× the human drift frequency . That looks manageable — a meaningful gap, but not alarming. The PDR was 22× the human reference . Not 22% more. 22 times more costly to fix. The frequency gap makes Security & Privacy drift look like a minor concern. The PDR reveals it’s the most expensive problem in the dataset. AI-generated security drift (client-side authorization gates bypassable in DevTools, raw PII and credentials passed through props without tokenization) is syntactically identical to safe code. It passes review, but the fixe