GPT-5 has demonstrated a significant leap in reasoning capabilities, particularly in AI code review, outperforming other models such as Opus-4, Sonnet-4, and OpenAI's O3 in various tests. CodeRabbit's evaluation of GPT-5, which involved complex pull requests, highlighted its superior ability to detect bugs, achieving an 85% success rate compared to the 16-22% lower rates of other models. The model excelled in the most challenging tests, achieving a 77.3% pass rate, showing notable improvements over its competitors. GPT-5's advanced reasoning was further evidenced in its ability to identify and propose comprehensive solutions for intricate concurrency and security issues within codebases. The evaluation process involved both LLM-based and human assessments, focusing on review quality and accuracy. GPT-5's integration into CodeRabbit's pipeline is expected to enhance the depth and context of code reviews, offering a 14-day free trial for users to experience its capabilities firsthand.