GPT-5 (high) is the high-reasoning configuration of OpenAI's fifth-generation flagship model, released as part of the unified GPT-5 series on August 7, 2025. This variant is specifically optimized for complex analytical tasks, mathematical problem-solving, and advanced coding, often serving as the primary model for "thinking" modes where additional compute is allocated to deep reasoning before generating a final response.
Built on a multimodal transformer architecture, the model represents a shift toward agentic capabilities and integrated tool use. It is designed to minimize hallucinations and improve reliability across long-horizon tasks, demonstrating significant gains on benchmarks such as SWE-bench and MATH. The system employs adaptive compute, allowing it to dynamically adjust its internal processing cycles based on the perceived complexity of a query.
The model supports a substantial context window of 400,000 tokens through the OpenAI API, partitioned into 272,000 input tokens and 128,000 output tokens. While the core GPT-5 series is proprietary, it was launched alongside open-weight counterparts under the GPT-OSS family to provide a spectrum of options for developers and researchers. GPT-5 (high) is typically accessed as the default engine for high-tier professional and enterprise plans, emphasizing expert-level intelligence and multi-step reasoning depth.