How should you control long-running work with gpt-5.1-codex-max?

Set explicit task boundaries, tool permissions, time limits, and review checkpoints. Begin in a sandbox where intermediate changes and final output can be inspected.

Does gpt-5.1-codex-max charge more for long inputs?

GPT-5.1-Codex-Max uses a single published rate for input, regardless of request length; see the pricing table for the applicable amount.

How do you get a cache hit on gpt-5.1-codex-max?

To get a cache hit on gpt-5.1-codex-max, send requests with identical prompt prefixes. The cache is keyed by the beginning of your prompt; as long as the prefix matches a previous request, subsequent calls benefit from the lower cached rate. Keep system messages and initial context consistent across calls for best results.

What controls should you set before using gpt-5.1-codex-max in production?

Set task boundaries, review requirements, failure handling, and monitoring that match the consequences of the workload. Do not rely on an unevaluated model response for irreversible actions.

How should you begin a pilot with gpt-5.1-codex-max?

Use gpt-5.1-codex-max for supervised long tasks, then measure completion quality and token efficiency before expanding its scope.

Can you call gpt-5.1-codex-max with the SDK you already use?

Yes. gpt-5.1-codex-max is compatible with the standard SDK. Set the model parameter to gpt-5.1-codex-max and use your MixRoute API key. If your current code already calls the compatible API, changing the base URL and model ID is typically all that is needed.

How does gpt-5.1-codex-max compare with other models, and what should you compare?

Compare gpt-5.1-codex-max against models of similar capability and pricing on your actual workload. Evaluate latency, output quality, instruction following, and cost per task. Run side-by-side tests with your own prompts — the best model depends on your specific use case, not just benchmark scores.

Model detail

GPT-5.1-Codex-Max

Provided by OpenAI

Pay-as-you-go

GPT-5.1-Codex-Max is OpenAI’s latest agentic coding model, designed for long-running, high-context software development tasks. It is based on an updated version of the 5.1 reasoning stack and trained on agentic workflows spanning software engineering, mathematics, and research. GPT-5.1-Codex-Max delivers faster performance, improved reasoning, and higher token efficiency across the development lifecycle.

Model specs

Model ID: gpt-5.1-codex-max

Context length: 400K
Max output: 128K
I/O modalities
Released: 2025-12

API endpoints

One MixRoute gateway, OpenAI-compatible

OpenAI-compatible /v1/chat/completions POST

Pricing

Flat rate, unit: /1M Tokens

Input

$1.2500 /1M Tokens

Completion

$10.0000 /1M Tokens

Selection summary

Quickly judge whether it fits your workload

What is this model good for?

Codex model for coding and agentic tasks

GPT-5.1-Codex-Max: GPT‑5.1-Codex-Max is purpose-built for agentic coding. It's only available in the Responses API. Learn how to get the most of GPT-5.1-Codex-Max in the prompting guide.. 400,000-token context.

What should you check before using it?

400,000 context, 128,000 output

OpenAI model. Supports tool calling, structured outputs, function calling. Knowledge cutoff: 2024-09-30.

Why use it through MixRoute?

Drop-in via OpenAI-compatible endpoint on MixRoute

Set the model parameter to "gpt-5.1-codex-max" and use your MixRoute API key.

Capabilities & compatibility

Unconfirmed capabilities stay "Unknown," no guesses

Tool calling

GPT-5.1-Codex-Max supports function and tool calls.

EX Send a tools definition; the response returns tool_calls to execute and feed results back.

Structured output

GPT-5.1-Codex-Max can produce JSON-formatted output on demand.

EX response_format: { type: "json_schema" } forces valid JSON output.

Streaming

GPT-5.1-Codex-Max supports streamed responses.

EX stream: true streams tokens incrementally, so chat UIs render as they arrive.

Prompt caching

GPT-5.1-Codex-Max supports prompt caching under supported routing conditions.

EX Keep the system prompt and tool definitions at the start of the request; repeated prefixes are automatically billed at the cache-read rate.

Vision input

GPT-5.1-Codex-Max can process image inputs alongside text.

EX Pass a base64-encoded image in a image_url content part alongside text messages.

OpenAI SDK

Call GPT-5.1-Codex-Max through MixRoute's OpenAI-compatible endpoint.

EX Change base_url to https://api.mixroute.ai/v1; everything else follows the OpenAI style.

Token cost estimator

Live estimate from this page's pricing, not an actual bill

Input tokens Max per request 400K

Output tokens Max per request 128K

Requests / month

Cache hit rate –

This model has no cache-read price; caching is not counted

FAQ

gpt-5.1-codex-max is intended for long-running, high-context software development work across engineering, mathematics, and research-oriented workflows.

Get started

01

Create an API key

Generate a key in the Console; one key calls every model.
02

Set the base URL

Fully OpenAI SDK-compatible; just swap the URL to connect.

https://api.mixroute.ai/v1
03

Specify the model ID

In the request's model field, enter:

gpt-5.1-codex-max

Create an API key

New users get $5 in free credits

Test this model and alternate routes with the same request format

Start from a real workload, then let quality, total cost, and failure conditions decide whether to send production traffic.

Create an API key View integration docs