GPT-5.1 Codex Max
Access GPT-5.1 Codex Max through one API key. Max-output coding model.
OpenAI's earlier generation max-output coding model. 128K output tokens for generating entire codebases.
No credit card required. Takes 30 seconds.
2,400+
Developers
1.2M+
API calls served
100+
Endpoints
$0.01
Per call
Yep, that's it.
Try it live
Send a message and see GPT-5.1 Codex Max respond in real time.
Maximum tokens in the response.
Real-time tokens
Context Window
400K tokens
Max Output
128K tokens
Input Price
$1.75 / 1M tokens
Output Price
$14.00 / 1M tokens
Strengths
GPT-5.1 Codex Max supports up to 128,000 output tokens, letting it generate entire files or large codebases in a single response.
A 400,000-token context window lets it read large, multi-file projects before generating code.
Built to scaffold whole applications — routes, models, and configuration — in one pass rather than fragment by fragment.
At $1.75 per 1M input and $14.00 per 1M output tokens, it is the most affordable of these large-output OpenAI coders.
Quick start
Copy this snippet and start making calls with GPT-5.1 Codex Max.
const res = await fetch('https://api.yepapi.com/v1/ai/chat', {
method: 'POST',
headers: {
'x-api-key': 'YOUR_API_KEY',
'Content-Type': 'application/json',
},
body: JSON.stringify({
"model": "openai/gpt-5.1-codex-max",
"messages": [
{
"role": "user",
"content": "Explain API gateways in 2 sentences."
}
],
"maxTokens": 256
}),
});
const { data } = await res.json();
console.log(data.message.content);Why use GPT-5.1 Codex Max through YepAPI?
GPT-5.1 Codex Max API: max-output coding for whole codebases
GPT-5.1 Codex Max is OpenAI's earlier-generation max-output coding model, built to generate entire codebases with up to 128K output tokens and a 400K context window. At $1.75 per 1M input tokens and $14.00 per 1M output tokens, it is the most cost-effective large-output coder in this lineup.
Through YepAPI you reach GPT-5.1 Codex Max with one OpenAI-compatible API key. The same key also covers other models and YepAPI's SEO, SERP, and web-scraping endpoints, so you can generate full apps and collect data from one account.
What is GPT-5.1 Codex Max?
GPT-5.1 Codex Max is OpenAI's earlier-generation coding model optimized for maximum output. Its defining feature is the ability to emit up to 128,000 tokens in a single response, which lets it scaffold entire applications — routes, data models, configuration, and tests — in one pass rather than piecemeal. A 400,000-token context window lets it read large existing projects before generating. Compared with later Codex releases it is positioned as the budget-friendly large-output option, at $1.75 per 1M input and $14.00 per 1M output tokens, making big code generations affordable.
Build with GPT-5.1 Codex Max via YepAPI
Call the OpenAI-compatible /v1/ai/chat endpoint with your YepAPI key. The Chat Completions schema means existing SDKs and code agents work after changing the base URL and model name. Lean on its 128K output to scaffold complete projects in a single call — for example a full app with auth, models, and API routes. One key also unlocks other models plus SEO, SERP, and scraping APIs, so the generated app can be paired with data tooling through one integration.
GPT-5.1 Codex Max API pricing — $1.75 / $14.00 per 1M tokens
GPT-5.1 Codex Max costs $1.75 per 1M input tokens and $14.00 per 1M output tokens, the lowest large-output coding rate in this set. Since its strength is generating very large responses, the favorable output price is what makes whole-codebase generation practical. Billing is per token, so smaller jobs stay cheap and you only pay for the volume of code actually produced.
GPT-5.1 Codex Max for full codebase generation
The model is built for greenfield generation: scaffolding a complete Next.js app, building an entire CRUD service, or producing a full feature set with its supporting files in one response. The 128K output means it does not have to stop and continue, and the 400K context lets it match an existing project's conventions. When the task is 'generate the whole thing,' GPT-5.1 Codex Max is a cost-effective fit.
Try GPT-5.1 Codex Max free
New YepAPI accounts include $5 in free credit with no card required. That is enough to have GPT-5.1 Codex Max scaffold a real project end to end so you can judge its large-output code generation before committing.
Start generating in 30 seconds
$5 free credit on signup. No credit card required. Pay per call.
What developers say
“Switched from SerpAPI and cut our SERP costs by 80%. Same data quality, way simpler billing.”
“One API key for AI models, SERP data, and web scraping. Saved us from managing 4 separate providers.”
“The $5 free credit let us prototype our entire rank tracking feature before committing. No other API does that.”
Frequently asked questions
OpenAI's earlier generation max-output coding model. 128K output tokens for generating entire codebases.
Input tokens cost $1.75 per 1M tokens and output tokens cost $14.00 per 1M tokens through YepAPI. No monthly minimums — you only pay for what you use.
Sign up for a free API key, then send requests to the /v1/ai/chat endpoint.
GPT-5.1 Codex Max supports a 400K token context window with up to 128K output tokens per request.
Ready to use GPT-5.1 Codex Max?
$5 free credit on signup. No credit card required. Pay per call.
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