Can AI Completely Rewrite Legacy Code?

AI can generate code, build apps, and even refactor existing projects—but can it fully rewrite a legacy application? I put three AI models to the test: Qwen 2.5 Max, DeepSeek R1, and ChatGPT.

For this experiment, I gave them an old C# ASP.NET lottery simulation tool I wrote back in 2013/2014. This wasn’t just a simple script—it was a full project with multiple files, classes, and complex interactions. Could AI handle the challenge?

🔍 The Results:
✅ ChatGPT was the only model that could accept and analyze the full project.
❌ Qwen 2.5 Max & DeepSeek R1 failed immediately—they couldn't handle multiple files or a zipped solution.

🤔 ChatGPT inferred the intent of the code but could only generate code stubs, not a complete rewrite.

The Verdict:
AI is powerful, but it's not quite there yet when it comes to fully rewriting complex legacy applications. It can assist with refactoring and suggest improvements, but a production-ready rewrite still needs human expertis