Code cloning (duplication)
Copy-pasted or near-identical blocks of code; a maintainability cost that rose sharply with AI assistants.
Assistants generate fresh code rather than reusing existing functions, so duplication grows. GitClear's analysis of 211M changed lines found the number of duplicated 5+ line blocks grew 4× from 2020 to 2024, copy/pasted lines rose from 8.3% to 12.3% of changes, and 'moved' (refactored) lines fell from ~25% to under 10%. Duplication increases the surface for bugs and makes changes more expensive later.