New GPT-5.1-Codex-Max Model Boosts Coding Efficiency by 30%

OpenAI has recently introduced two distinct yet complementary AI models, GPT-5.1-Codex-Max and GPT-5.1 (non-codex), each optimized for different stages of the software development workflow. A recent social media post by Haider highlighted these specialized applications, advising users to leverage their unique strengths for maximum productivity. This strategic differentiation aims to streamline development processes by aligning specific model capabilities with task requirements.

GPT-5.1-Codex-Max is positioned as a frontier agentic coding model, excelling in execution tasks that require precise and tight instructions. According to OpenAI, this model demonstrates significant improvements in token efficiency, achieving better performance while using 30% fewer thinking tokens on SWE-bench Verified compared to its predecessor, GPT-5.1-Codex. Its design focuses on long-running, detailed work, capable of coherently operating across multiple context windows through a process called "compaction."

Conversely, the standard GPT-5.1 (non-codex) model is recommended for more abstract tasks such as planning, understanding, and guidance. As Haider stated in the tweet, "> gpt-5 / 5.1 (non-codex) is better for planning, understanding, and guidance so plan with non-codex, then execute with codex." This approach suggests a workflow where the non-codex version lays the groundwork, and the Codex-Max model then implements the detailed execution.

GPT-5.1-Codex-Max is now available in public preview for GitHub Copilot users, including Copilot Pro, Business, and Enterprise plans. OpenAI's internal evaluations have shown the model working independently for over 24 hours on complex tasks, representing a significant leap in sustained autonomous work. This capability allows for project-scale refactors, deep debugging sessions, and multi-hour agent loops without constant human intervention.

The new model is built on an updated foundational reasoning model trained on agentic tasks across various domains, including software engineering, math, and research. Its enhanced performance is evident in benchmarks, where it often edges out competitors like Gemini 3 Pro in agentic coding tasks. OpenAI emphasizes that GPT-5.1-Codex-Max is specifically tailored for agentic coding within Codex or similar environments, differentiating it from the general-purpose GPT-5.1.