Meta Description: Discover GPT-5.1 Codex Max – OpenAI’s groundbreaking agentic coding model with compaction technology, 24+ hour autonomous operation, and superior benchmark performance.
Imagine an AI that can work alongside you for over 24 hours straight, tackling the most complex coding challenges without losing focus or context. Sounds like science fiction? Well, it’s not anymore. GPT-5.1 Codex Max has arrived, and it’s rewriting the rules of what AI can do for software developers worldwide.
Released by OpenAI on November 19, 2025, GPT-5.1 Codex Max represents a quantum leap in agentic coding technology. Whether you’re in China, India, Russia, the USA, or anywhere else on the planet, this model is poised to transform how you write, debug, and ship code. I’ve been diving deep into its capabilities, and let me tell you – the hype is real.
In this comprehensive guide, I’ll walk you through everything you need to know about GPT-5.1 Codex Max. From its groundbreaking compaction feature to real-world benchmarks that outpace the competition, we’re covering it all. Grab your coffee – this is going to be good.
GPT-5.1 Codex Max is OpenAI’s frontier agentic coding model, specifically designed for long-running, high-context coding tasks. Unlike its predecessors or general-purpose AI models, this beast is built from the ground up to handle complex software engineering workflows that would make other models tap out.
Here’s what makes GPT-5.1 Codex Max special: it’s the first model natively trained to operate across multiple context windows through a revolutionary process called compaction. This allows it to work coherently over millions of tokens in a single task – something that was previously impossible.
Key Features of GPT-5.1 Codex Max:
If you’ve used GPT-5.1-Codex before, you might be wondering what the big deal is. The answer lies in both architecture and capability. GPT-5.1 Codex Max isn’t just an incremental upgrade – it’s a fundamental reimagining of how AI coding assistants should work.
The standout feature of GPT-5.1 Codex Max is its compaction capability. Think of it like this: when you’re working on a massive codebase, traditional models eventually run out of memory – they hit their context window limit and start forgetting important details. Compaction solves this by intelligently pruning history while preserving the most critical context.
In practice, this means GPT-5.1 Codex Max can tackle project-scale refactors, deep debugging sessions, and multi-hour agent loops that would have been impossible before. OpenAI’s internal testing showed the model completing tasks that ran for more than 24 hours continuously.
| Feature | GPT-5.1 Codex Max | GPT-5.1-Codex | GPT-5-Codex |
|---|---|---|---|
| SWE-Bench Verified | 77.9% | 73.7% | ~70% |
| Terminal Bench 2.0 | 58.1% | 52.8% | ~48% |
| Compaction Support | Native | Limited | No |
| Windows Support | Yes | Limited | No |
| Token Efficiency | 30% fewer | Baseline | Higher usage |
So what can you actually do with GPT-5.1 Codex Max? The answer is: quite a lot. Here are the primary use cases where this model truly shines.
Have you ever inherited a legacy codebase that made you want to cry? GPT-5.1 Codex Max can migrate entire repositories from one framework to another. OpenAI demonstrated it migrating a React 17 codebase to React 19 with concurrent mode implementation – completing in under 8 hours what would take a team of developers several days.
The model excels at creating pull requests and conducting thorough code reviews. It doesn’t just spot syntax errors – it reasons over dependencies, validates behavior against tests, and catches critical flaws that human reviewers might miss. This is where the GPT-5.1 Codex Max code review capability really stands out.
Security-conscious teams will appreciate the GPT-5.1 Codex Max for vulnerability discovery capabilities. While OpenAI notes it doesn’t reach “High” capability under their Preparedness Framework, it’s currently the most capable cybersecurity model they’ve deployed. It can scan repositories for vulnerabilities, propose patches, and verify fixes.
Additional powerful use cases include:
Getting your hands on GPT-5.1 Codex Max is straightforward. The model is available through multiple channels, each suited to different workflows and needs.
Current Access Methods:
npm i -g @openai/codex and start using immediatelyFor ChatGPT subscribers, GPT-5.1 Codex Max is available on Plus, Pro, Business, Edu, and Enterprise plans. The model has replaced GPT-5.1-Codex as the default across all Codex surfaces.
Here’s some surprisingly good news. The GPT-5.1 Codex Max pricing is remarkably competitive – OpenAI set it at the same rate as the base GPT-5 model, which is unusual for a specialized, high-performance variant.
| Token Type | Price per 1M Tokens |
|---|---|
| Input Tokens | $1.25 |
| Output Tokens | $10.00 |
| Cached Input (90% savings) | $0.125 |
Compared to Claude Sonnet 4.5 ($3/$15 per 1M tokens), GPT-5.1 Codex Max offers significant cost savings – especially when you factor in its improved token efficiency. Real-world testing has shown tasks costing 43% less than competing models while delivering code that actually works.
GPT-5.1 Codex Max supports virtually every mainstream programming language, with particularly strong performance in languages commonly used for enterprise and web development.
The GPT-5.1 Codex Max Windows support is a game-changer for developers in enterprise environments. Previous Codex models were optimized primarily for Unix-based systems, leaving Windows developers at a disadvantage. That’s no longer the case.
The AI coding landscape has never been more competitive. Let’s see how GPT-5.1 Codex Max vs Gemini 3 and GPT-5.1 Codex Max vs Claude comparisons actually play out.
| Metric | GPT-5.1 Codex Max | Claude Sonnet 4.5 | Gemini 3 Pro |
|---|---|---|---|
| SWE-Bench Verified | 77.9% | 77.2% | 76.2% |
| Terminal Bench 2.0 | 58.1% | 50.0% | 54.2% |
| Input Pricing (1M) | $1.25 | $3.00 | ~$1.25 |
| Long-Horizon Tasks | 24+ hours | ~5.5 hours | Varies |
GPT-5.1 Codex Max leads on SWE-Bench Verified by a narrow margin, but its dominance on Terminal Bench 2.0 is more significant – reflecting superior performance in long-running, terminal-based development workflows. The cost advantage is substantial when compared to Claude, making it an attractive option for teams watching their budgets.
The GPT-5.1 Codex Max compaction feature deserves a deeper explanation because it’s genuinely revolutionary. Here’s how it works in practice.
When you’re working on a complex task, GPT-5.1 Codex Max monitors its context window usage. As the session approaches the context limit, the model automatically invokes compaction – intelligently pruning less important information while preserving critical context about files, decisions, and ongoing work.
This isn’t just simple summarization. The compaction process is deeply integrated with the model’s training, allowing it to maintain coherent work across what effectively becomes millions of tokens. In API usage, developers can invoke /compact to manually trigger this process when needed.
Key benefits of compaction:
Absolutely – and this is where GPT-5.1 Codex Max for software engineering really earns its keep. The model is specifically designed for large-scale, enterprise-grade software development.
OpenAI’s internal data is compelling: 95% of their engineers use Codex weekly, and these engineers ship roughly 70% more pull requests since adopting Codex. When you extrapolate this to GPT-5.1 Codex Max, with its improved capabilities, the productivity gains are likely even higher.
The model’s integration with GitHub Copilot integration through the public preview makes it particularly accessible for teams already using Copilot. Whether you’re using Visual Studio Code, GitHub.com, GitHub Mobile, or the Copilot CLI, GPT-5.1 Codex Max is ready to augment your workflow.
Let’s talk numbers. The performance improvements in GPT-5.1 Codex Max are measurable and significant across multiple dimensions.
On SWE-bench Verified, GPT-5.1 Codex Max with ‘medium’ reasoning effort achieves better performance than GPT-5.1-Codex at the same reasoning effort while using 30% fewer thinking tokens. This translates directly to cost savings and faster response times.
The model introduces a new ‘xhigh’ (extra high) reasoning effort level. While ‘medium’ is recommended as the daily driver for most tasks, ‘xhigh’ provides extended thinking time for the most challenging problems – like complex architectural decisions or multi-step refactoring projects.
In practical testing, developers report GPT-5.1 Codex Max producing high-quality frontend designs at significantly lower cost than previous models. The model is particularly adept at creating interactive applications – demonstrated examples include CartPole reinforcement learning sandboxes and Snell’s Law physics explorers, all generated from natural language prompts.
The GPT-5.1 Codex Max for IDE integration story is robust and growing. Here’s the current landscape:
For developers who prefer working directly in the terminal, the Codex CLI remains the most powerful way to leverage GPT-5.1 Codex Max. It can inspect directory trees, manipulate files, invoke compilers, run tests, and interact with version control – all while maintaining the extended context that makes complex projects feasible.
1. Is GPT-5.1 Codex Max available for free?
No, GPT-5.1 Codex Max requires a paid subscription. It’s available to ChatGPT Plus ($20/month), Pro ($200/month), Business, Edu, and Enterprise users. API access follows standard OpenAI pricing at $1.25 per million input tokens and $10 per million output tokens.
2. Can I use GPT-5.1 Codex Max for general conversations?
OpenAI recommends using GPT-5.1 Codex Max only for agentic coding tasks in Codex or Codex-like environments. For general-purpose tasks, GPT-5.1 or GPT-5.2 are better choices.
3. How do I enable GPT-5.1 Codex Max in GitHub Copilot?
For Pro/Pro+ users, select the model in the Copilot Chat model picker and confirm the one-time prompt. For Enterprise/Business plans, administrators must first enable the GPT-5.1-Codex-Max policy in Copilot settings.
4. What is the GPT-5.1 Codex Max PR creation capability?
The GPT-5.1 Codex Max PR creation feature allows the model to autonomously create pull requests, complete with code changes, commit messages, and descriptions. It’s trained on real-world PR workflows and can iterate on implementations until tests pass.
Ready to dive deeper? Here are the best resources to master GPT-5.1 Codex Max:
| Resource | Description |
|---|---|
| OpenAI Official Documentation | Complete API reference and guides at openai.com |
| OpenAI Cookbook Prompting Guide | Official best practices for getting optimal results |
| GitHub Copilot Integration | Public preview documentation and setup guides |
| GPT-5.1 Codex Max System Card | Technical specifications and safety measures |
| DataCamp Tutorial | Hands-on project-based learning course |
GPT-5.1 Codex Max represents a genuine leap forward in AI-assisted software development. Its combination of native compaction, superior benchmark performance, competitive pricing, and broad platform integration makes it a compelling choice for developers and engineering teams worldwide.
Whether you’re tackling legacy code migrations, building new features, or just trying to ship more pull requests, GPT-5.1 Codex Max offers capabilities that simply weren’t possible a year ago. The fact that it can work autonomously for 24+ hours while maintaining context across millions of tokens isn’t just impressive – it’s transformative.
The AI coding assistant landscape is more competitive than ever, with Claude, Gemini, and other players pushing boundaries. But GPT-5.1 Codex Max has carved out a clear position at the frontier – particularly for teams that need sustained, long-horizon coding assistance at a reasonable price.
Ready to level up your development workflow? Install the Codex CLI today (npm i -g @openai/codex), enable GPT-5.1 Codex Max in GitHub Copilot, or explore the API documentation. The future of coding is here – and it’s more powerful than you might think.
Share your experience with GPT-5.1 Codex Max in the comments below! What projects are you tackling with this groundbreaking AI coding model?
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OpenAI Official Site
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OpenAI Research Page
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Gemini Model (Benchmark Competitor)
https://deepmind.google/technologies/gemini/ (do follow)
Anchor: Google Gemini AI model
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