GPT-5.1 Codex mini (high) is a specialized reasoning model developed by OpenAI, specifically engineered for high-performance software development and technical problem-solving. Released in November 2025 as part of the GPT-5.1 model family, it serves as a computationally efficient alternative to larger flagship models while maintaining sophisticated intelligence through inference-time reasoning. The "(high)" designation indicates that the model is configured for high reasoning effort, utilizing internal chain-of-thought processing to handle complex architectural logic and multi-step technical instructions. The model is multimodal, supporting both text and image inputs, which enables it to interpret technical diagrams, UI mockups, and codebase visualizations. It features a significant context window of 400,000 tokens, allowing for the analysis of entire repositories and extensive documentation within a single session. Compared to the "Instant" variants in the same series, the Codex mini (high) prioritize accuracy and depth, excelling in tasks such as autonomous debugging, complex code refactoring, and mathematical proofing. While highly capable, the model is noted for its verbosity in reasoning outputs and utilizes an asymmetric pricing structure optimized for input-heavy, output-light engineering tasks.
