Claude Opus 4 solves a 4-year-old bug that an expert coder and other AIs Like ChatGPT, Gemini couldn't fix

Claude AI

Anthropic’s latest AI model Claude Opus 4 has done what top AI tools and even a highly experienced developer couldn’t pull off in years– it solved a mysterious bug that had gone unresolved for four years.

A Reddit user who goes by the handle u/grafxflow, and identifies as a veteran C++ developer with over 30 years of experience (including a stint as a Staff Engineer at a FAANG company), shared a detailed post about how Claude helped him solve what he calls his “white whale bug.”

“This was a bug I couldn’t find for four years,” he wrote. “Even ChatGPT-4.1, Gemini 2.5, and older versions of Claude made zero progress. But Claude Opus 4 nailed it.”

As per the coder, the bug originated from a massive 60,000-line refactor of code related to shader behavior in a graphics application. While the overhaul fixed many issues, it broke a particular shader in a very specific edge case. “It used to work, then we rearchitected and refactored, and it no longer worked,” the developer explained. “I’ve probably spent 200 hours on it over the years.”

Despite his expertise—he’s the kind of engineer others rely on when they’re stuck—this problem remained unsolved. That is, until he tried Claude Opus 4.

“I gave it access to both the old and new codebases and asked it to find where the change happened. It took about 30 prompts and one restart,” he said. “Turns out the bug wasn’t a simple logic issue. The old system had a behavior that just happened to work by coincidence, and that behavior didn’t carry over to the new architecture. Claude figured that out.”

What stunned him most was that no other AI could even get close. “Opus 4 found it. I’m humbled,” he admitted.

The post has since sparked conversations in developer circles about the potential of next-gen AI tools not just for writing code, but for truly understanding complex systems and debugging them in ways even experts miss.

For many, it’s a reminder that the future of AI-assisted programming is already here and it might just save you hundreds of hours of head-scratching.