gpt-5-1-codex-max
GPT-5.1-Codex-Max is OpenAI’s agentic coding model for long-running, high-context software development, based on an updated version of the 5.1 reasoning stack and trained on agentic coding tasks.
Pricing: Input 300 credits / 1M tokens (≈ $1.50), Output 2400 credits / 1M tokens (≈ $12.00).
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GPT-5.1-Codex-Max API on ModelFold
GPT-5.1-Codex-Max is OpenAI’s agentic coding model for long-running, high-context software development, based on an updated version of the 5.1 reasoning stack and trained on agentic coding tasks. Try GPT-5.1-Codex-Max in the ModelFold Playground, then call it from your own code through an OpenAI-compatible chat completions API.
What Is the GPT-5.1-Codex-Max API
GPT-5.1-Codex-Max at a glance
GPT-5.1-Codex-Max is a chat model from OpenAI. It accepts text and images as input and returns text, with a context window of up to 400K tokens.
Use it without hosting anything
On ModelFold you call GPT-5.1-Codex-Max with a single API key — no model weights to download and no inference servers to run. The same key also works for the other chat, image, video and audio models on ModelFold.
Core Capabilities of GPT-5.1-Codex-Max
Up to 400K tokens of context
Keep long conversations, large documents and sizeable code in a single request, so the model can reason over the full material instead of fragments.
Understands images
Besides text, GPT-5.1-Codex-Max accepts images as input, so a single request can combine instructions with visual or other media.
Function calling
GPT-5.1-Codex-Max supports tool (function) calling: describe your functions in the request and the model returns structured calls your code can run — the basis for agents and integrations.
Adjustable reasoning effort
Choose a reasoning effort level (low, medium or high) per request to balance depth of thinking against speed and token usage.
Structured outputs
Ask for JSON that follows a schema (response_format), which makes extraction, classification and system integrations more reliable.
How to Use GPT-5.1-Codex-Max on ModelFold
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Step 1: Try it in the Playground
Open the Playground at the top of this page, type a prompt and see how GPT-5.1-Codex-Max responds before writing any code.
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Step 2: Create an API key
Sign in to ModelFold and create an API key in the console. Keep it secret and send it as a Bearer token.
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Step 3: Send a request
Call POST https://modelfold.ai/v1/chat/completions with "model": "gpt-5-1-codex-max" and your messages. Existing OpenAI-compatible SDKs work by changing the base URL and key.
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Step 4: Ship and monitor
Integrate the response into your product and check token usage and spend for every call in the console logs.
What You Can Build with GPT-5.1-Codex-Max
AI coding assistants
Generate, explain, debug and refactor code, review pull requests and work through multi-file changes in developer tools and IDE plugins.
Autonomous agents
Build agents that plan multi-step tasks, call your tools and APIs, and keep working toward a goal across long sessions.
Long-document workflows
Feed in long reports, contracts, manuals or codebases and ask for summaries, comparisons and answers grounded in the material.
Tool-calling backends
Route requests, call functions and chain API calls as the worker model inside larger agent systems.
Frequently Asked Questions
What is GPT-5.1-Codex-Max?⌄
GPT-5.1-Codex-Max is OpenAI’s agentic coding model for long-running, high-context software development, based on an updated version of the 5.1 reasoning stack and trained on agentic coding tasks.
Which inputs does GPT-5.1-Codex-Max support?⌄
GPT-5.1-Codex-Max accepts text and images and returns text. Through ModelFold you can send text and images (OpenAI-style image_url content); in the Playground you can also attach documents, which are converted to text.
How long is the context window of GPT-5.1-Codex-Max?⌄
Up to 400K tokens, shared between your input and the model’s output.
Does GPT-5.1-Codex-Max support function calling?⌄
Yes. GPT-5.1-Codex-Max supports tools / function calling through the standard tools parameter of the chat completions API.
How is GPT-5.1-Codex-Max billed on ModelFold?⌄
Pay as you go by tokens: input and output tokens are charged at the per-million-token prices shown on this page. There is no monthly fee, and failed requests are not charged.
How do I call GPT-5.1-Codex-Max through the API?⌄
Send a POST request to https://modelfold.ai/v1/chat/completions with "model": "gpt-5-1-codex-max", using your ModelFold API key as the Bearer token.
| Input | 300 credits 1M tokens≈ $1.50 |
| Output | 2400 credits 1M tokens≈ $12.00 |
Billed per token: input and output are priced separately, and thinking tokens count as output. The Playground charges exactly the same way.
Read API docs →AI Agents · Claude Code / Cursor / Trae →curl https://modelfold.ai/v1/chat/completions \
-H "Authorization: Bearer $MODELFOLD_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model":"gpt-5-1-codex-max","messages":[{"role":"user","content":"Hello"}]}'