Study: AI Coding Tools Generate Drift Up to 22x Costlier to Fix Than Human Code

A controlled study by ReWeaver AI tested five AI coding tools — Cursor, Claude Code, Lovable, Figma Make, and VS Code with Copilot — using 42 identical prompts across eight production-readiness dimensions, comparing outputs against a human-authored baseline. Researchers introduced a metric called the Production Drift Ratio (PDR), which weights how often code issues occur by their estimated remediation cost, rather than counting occurrences alone. While AI tools produced only 3.4 times the human drift frequency in Security and Privacy, the PDR for that dimension was 22 times higher, meaning the fixes were far more expensive and time-consuming. Across all eight dimensions, AI-generated code was consistently more costly to remediate than human-written code, even in areas where humans produced drift more frequently. Statistical testing confirmed the PDR gap was highly significant, while frequency alone showed no significant difference — highlighting that raw occurrence counts can mask the true cost of AI code quality issues.