OpenAI: GPT-5.1-Codex

GPT-5.1-Codex is a specialized version of GPT-5.1, meticulously optimized for software engineering and coding workflows. This powerful AI is designed for both interactive development sessions and the long, independent execution of complex engineering tasks. It excels at building projects from scratch, feature development, debugging, large-scale refactoring, and comprehensive code reviews. Compared to the base GPT-5.1, Codex is more steerable, adheres closely to developer instructions, and consistently produces cleaner, higher-quality code outputs. Its reasoning effort can be finely adjusted using the `reasoning.effort` parameter. Codex seamlessly integrates into various developer environments, including the CLI, IDE extensions, GitHub, and cloud tasks. It intelligently adapts its reasoning effort dynamically, providing fast responses for small tasks while sustaining extended multi-hour runs for large projects. The model is expertly trained to perform structured code reviews, identifying critical flaws by reasoning over dependencies and validating behavior against tests. It also supports multimodal inputs, such as images or screenshots for UI development, and integrates tool use for search, dependency installation, and environment setup. With a context window of 400K tokens and a max output of 128K tokens, and pricing at $1.25/10.00 per 1M tokens (input/output), Codex is specifically intended for advanced agentic coding applications.