GPT-5.1-Codex-Max

Name: OpenAI: GPT-5.1-Codex-Max
Brand: openai
SKU: openai/gpt-5.1-codex-max
Price: 1.375 USD
Availability: InStock

openai/gpt-5.1-codex-max

GPT-5.1-Codex-Max is OpenAI’s latest agentic coding model, designed for long-running, high-context software development tasks.

$1.375 in · $11.00 out per 1M tokens400k contextDec 4, 2025

about 0.6¢ a message

A typical message: about 500 tokens you send and 500 it writes.

Chat with GPT-5.1-Codex-Max

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Spec sheet

Published facts from the catalog, billed prices and what we measured here. Anything not measured says so.

Price, billed here

Input, per 1M tokens: $1.375provider $1.25
Output, per 1M tokens: $11.00provider $10.00
Cached input, per 1M: $0.1375provider $0.125
Margin: +10%

Context and formats

Context window: 400,000 tokens
Longest answer: 128,000 tokens
Reads: text and images
Makes: text
First listed: 2025-12-04

Measured here, last 7 days

First token, median: not measured
Answered without error: not measured

Tools and JSON

Tool calling: declaredthe provider's claim, not yet measured here
JSON output: declaredthe provider's claim, not yet measured here

Price and latency history as JSON: GET /api/planet/history?id=openai/gpt-5.1-codex-max.

About

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...

In OpenAI's words.

Try it here

Cmd+Enter sends

The answer appears here.

Measured here

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Call it

Use one OpenAI compatible endpoint, this model's id and an am_live_ key from the dashboard. You can also try it in chat first with no key.

curl https://useantimatter.com/v1/chat/completions \
  -H "Authorization: Bearer $ANTIMATTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "openai/gpt-5.1-codex-max", "messages": [{"role": "user", "content": "Hello"}]}'

Everything else is in the docs.

Embed this

A badge showing this model's live price per million tokens, as billed here, for a README or a site. It links back to this page.

<a href="https://useantimatter.com/planet/openai/gpt-5.1-codex-max"><img src="https://useantimatter.com/api/badge/price?id=openai%2Fgpt-5.1-codex-max" alt="GPT-5.1-Codex-Max price on Antimatter" height="28"></a>

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