GPT-5.1-Codex-Max

GPT-5.1-Codex-Max is a specialized agentic model engineered to serve as a reliable partner for complex software development workflows. Built upon an updated foundational reasoning architecture, the model is designed to handle demanding tasks across mathematics, research, and engineering. Its primary innovation is a technique called compaction, which allows the model to manage multiple context windows coherently. This capability enables it to process millions of tokens in a single session, making it well-suited for large-scale code refactors, deep debugging, and multi-hour agentic loops that require sustained focus.

The model’s training lineage is rooted in real-world software engineering scenarios, including pull request creation, code reviews, and frontend development. It is the first model in its class trained to operate natively within Windows environments and is optimized for collaborative interaction within the command-line interface. By leveraging improved token efficiency, the model delivers higher quality results while maintaining faster performance than previous generations. These advancements position it as a robust tool for enterprise-grade coding, providing developers with a persistent assistant capable of maintaining context over extended, day-long work cycles.