GPT-5 Nano is the smallest and fastest variant in the GPT-5 family, optimized for ultra-low latency and cost-sensitive environments. As the successor to GPT-4.1 Nano, it is purpose-built for developer tools, classification tasks, rapid interactions, and real-time applications where response speed takes priority over deep reasoning. Despite its compact size, it retains key instruction-following and safety features from the GPT-5 series.