The Hidden Cost of Code Duplication in AI-Assisted Development

This article was originally published on LucidShark Blog . AI coding agents are exceptional at generating code. They are also, structurally, among the worst duplicators in the history of software development. Here is why that matters more than you think - and how to stop it before it compounds. There is a number that comes up repeatedly in software engineering research: 20 to 30 percent. That is the fraction of code in a typical production codebase that is duplicated, according to studies by researchers at Carnegie Mellon, the Software Engineering Institute, and industry analyses from tools like SonarQube. In a 100,000-line codebase, you are carrying between 20,000 and 30,000 lines of redundant logic. Each one of those lines needs to be maintained, tested, and understood by every developer who reads the file. Before AI coding assistants, duplication grew slowly. A developer copy-pasted a utility function during a deadline crunch. A new engineer did not know the helper already existed i