At Greptile, the company uses AI-powered code reviews to detect intricate bugs in complex software. An evaluation was conducted to compare two OpenAI models, o1-mini and o3, on their ability to identify difficult-to-detect bugs. The results showed that OpenAI o3 substantially outperformed o1-mini across all programming languages, with a significant advantage in languages like Python, Rust, and Ruby. This is primarily due to o3's reasoning capability, which enables it to better understand complex code logic and identify intricate bugs, especially in syntax-driven contexts where pattern-matching alone may struggle. The evaluation highlighted the strength of OpenAI o3's reasoning capability through examples such as detecting a subtle Python method call error. Overall, this demonstrates that AI models with reasoning capabilities will become increasingly vital for ensuring software reliability and security as software complexity continues to increase.