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...
- 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 tokens | Provider | + 3% fee | You 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.
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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