OpenAI's GPT-5 has demonstrated groundbreaking capabilities as a multimodal generalist reasoner, particularly in clinical decision-making and advanced problem-solving benchmarks. The model, including its variants GPT-5-mini and GPT-5-nano, has been evaluated for zero-shot chain-of-thought reasoning across textual and visual inputs. GPT-5 achieved historic success on the FrontierMath benchmark by solving multiple Tier 4 problems, including two that had never been solved by any AI before, one authored by a judge of the FrontierMath Symposium. In medical reasoning, GPT-5 showed near-perfect accuracy on a high-quality ophthalmology question-answering dataset and outperformed human experts on the MedXpertQA multimodal benchmark by 24.23% in reasoning and 29.40% in understanding, and by 15.22% and 9.40% respectively on the text-only version of the benchmark. Additionally, GPT-5 leads the Elimination Game benchmark with a score of 4.86, ahead of competitors such as Grok 3 Mini Beta and Claude Opus 4.1. These results highlight GPT-5's advanced reasoning and understanding capabilities across multiple domains, including mathematics, medicine, and speech API implementation.