GPT-5 is OpenAI's unified frontier model released in mid-2025, bringing together advanced reasoning, coding, and multimodal capabilities into a single system. It introduced test-time compute scaling with configurable thinking depth, significantly reducing hallucinations and sycophancy compared to previous models. GPT-5 excels at complex multi-step tasks requiring step-by-step reasoning, instruction following, and accuracy in high-stakes scenarios, with notable improvements in coding, writing, and factual reliability.