GPT-5.1-Codex-Max
About this model
GPT-5.1-Codex-Max is an AI model from OpenAI, made available through the API on December 4, 2025. It can read up to 400,000 tokens in one request, roughly 750 pages of text, and write up to 128,000 tokens in a single answer. Besides text, it accepts images as input.
Through the API it costs $1.25 per million input tokens and $10 per million output tokens. It is among the more expensive models we track, a price usually reserved for the most capable, flagship-class models.
It supports extended reasoning: it can "think" step by step before answering, which helps on maths, code and complex questions. It can call tools and functions, so developers can connect it to search, databases or other software.
Quality scores
Rankings →Not rated yet. Independent test results usually appear a few weeks after a model is released.
Where to use it
Companies that serve this model through an API: 1. Prices per million tokens, cheapest first.
Availability and prices come from OpenRouter’s public API and are refreshed daily. Uptime is the share of successful requests over the last 24 hours. Some providers run a compressed version of open models (fp8, int4), which is cheaper but can be slightly less accurate.
Use it in your code
Call GPT-5.1-Codex-Max through OpenRouter’s OpenAI-compatible API: create a key on openrouter.ai, then run one of these examples.
curl https://openrouter.ai/api/v1/chat/completions \
-H "Authorization: Bearer $OPENROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model": "openai/gpt-5.1-codex-max", "messages": [{"role": "user", "content": "Hello! What can you do?"}]}'import os
from openai import OpenAI
client = OpenAI(base_url="https://openrouter.ai/api/v1", api_key=os.environ["OPENROUTER_API_KEY"])
reply = client.chat.completions.create(
model="openai/gpt-5.1-codex-max",
messages=[{"role": "user", "content": "Hello! What can you do?"}],
)
print(reply.choices[0].message.content)import OpenAI from "openai";
const client = new OpenAI({ baseURL: "https://openrouter.ai/api/v1", apiKey: process.env.OPENROUTER_API_KEY });
const reply = await client.chat.completions.create({
model: "openai/gpt-5.1-codex-max",
messages: [{ role: "user", content: "Hello! What can you do?" }],
});
console.log(reply.choices[0].message.content);The same code works with every model on this site: only the model ID changes. Many labs also offer their own API and SDK.
What it costs in practice
- 1,000 chat replies$3.63
- Summarise a 100-page document$0.073
- An app with 10,000 requests a day for a month$1,575
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News about OpenAI
See all →Frequently asked questions
- How much does GPT-5.1-Codex-Max cost?
- GPT-5.1-Codex-Max costs $1.25 per million input tokens and $10 per million output tokens through the API. For example, 1,000 chat replies of about 500 tokens in and 300 out cost around $3.63.
- What is the context window of GPT-5.1-Codex-Max?
- GPT-5.1-Codex-Max can read up to 400,000 tokens in one request, about 750 pages of text. It can write up to 128,000 tokens in a single answer.
- Is GPT-5.1-Codex-Max open source?
- No. GPT-5.1-Codex-Max is a closed model: its weights are not published, so you use it through OpenAI’s own apps and API, or through cloud providers.
- Who makes GPT-5.1-Codex-Max?
- GPT-5.1-Codex-Max is made by OpenAI. It became available through the API on December 4, 2025.
- Can GPT-5.1-Codex-Max read images?
- Yes. Besides text, it accepts images as input.
- What are the alternatives to GPT-5.1-Codex-Max?
- Models with a similar price from other companies include Muse Spark 1.3, Grok 4.3 and GLM 5V Turbo. You can compare them side by side on this page.