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OpenKey

GPT-5.1-Codex-Max

OpenAIReleased Dec 4, 2025

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...

Try in playground
Context window
400K tokens
Max output
128K tokens
Input
text, image
Output
text
Tokenizer
GPT
Released
Dec 4, 2025
Reasoning
always on

Pricing

Per 1M tokens. The provider price and our flat 3% fee are separate columns — what you pay is their sum.

Per 1M tokensProvider+ 3% feeYou pay
Input$1.25$0.037$1.29
Output$10.00$0.300$10.30
Cache read$0.125$0.0037$0.129

Supported parameters

  • include_reasoning
  • max_completion_tokens
  • max_tokens
  • reasoning
  • response_format
  • seed
  • structured_outputs
  • tool_choice
  • tools

Call it

OpenAI-compatible: point your SDK at api.openkey.ai/v1 and use model openai/gpt-5.1-codex-max.

Code sample language
curl https://api.openkey.ai/v1/chat/completions \
  -H "Authorization: Bearer $OPENKEY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.1-codex-max",
    "messages": [{"role": "user", "content": "Hello"}]
  }'
import os
from openai import OpenAI

client = OpenAI(
    base_url="https://api.openkey.ai/v1",
    api_key=os.environ["OPENKEY_API_KEY"],
)

completion = client.chat.completions.create(
    model="openai/gpt-5.1-codex-max",
    messages=[{"role": "user", "content": "Hello"}],
)
print(completion.choices[0].message.content)
import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.openkey.ai/v1",
  apiKey: process.env.OPENKEY_API_KEY,
});

const completion = await client.chat.completions.create({
  model: "openai/gpt-5.1-codex-max",
  messages: [{ role: "user", content: "Hello" }],
});
console.log(completion.choices[0].message.content);

Questions

How much does GPT-5.1-Codex-Max cost via API?
Through OpenKey, GPT-5.1-Codex-Max costs $1.29 per 1M input tokens and $10.30 per 1M output tokens. That is the provider price ($1.25 / $10.00) plus a flat 3% fee — nothing else.
What is GPT-5.1-Codex-Max's context window?
GPT-5.1-Codex-Max accepts up to 400K tokens of context and returns up to 128K tokens per request.
Is GPT-5.1-Codex-Max OpenAI-compatible?
Yes. Send requests to OpenKey's /v1/chat/completions endpoint with model "openai/gpt-5.1-codex-max" using any OpenAI SDK — only the base URL and API key change.
What inputs does GPT-5.1-Codex-Max support?
GPT-5.1-Codex-Max accepts text, image input and produces text output.

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