GPT 5.1 Codex Max
GPT 5.1 Codex Max applies maximum compute to the GPT-5.1 codex architecture, delivering the deepest reasoning and most thorough code analysis available in OpenAI's coding agent lineup for the most demanding software engineering tasks.
View API reference- Input and output price
- Input $1.25, Output $10, Per 1M tokens
- 24h uptime
- Loading AI Gateway uptime
import { streamText } from 'ai'
const result = streamText({ model: 'openai/gpt-5.1-codex-max', prompt: 'Why is the sky blue?'})Copy link to headingPlayground
Try out GPT 5.1 Codex Max by OpenAI. Usage is billed to your team at API rates. Free users (those who haven't made a payment) get $5 of credits every 30 days.
GPT 5.1 Codex Max
Copy link to headingProviders
Route requests across multiple providers. Copy a provider slug to set your preference. Visit the docs for more info. Using a provider means you agree to their terms, listed under Legal.
| Provider |
|---|
Copy link to headingUptime24 hours
Direct request success rate on AI Gateway and per-provider. Visit the docs for more info.
Copy link to headingThroughput24 hours
P50 throughput on live AI Gateway traffic, in tokens per second (TPS). Visit the docs for more info.
Copy link to headingLatency24 hours
P50 time to first token (TTFT) on live AI Gateway traffic, in milliseconds. View the docs for more info.
Getting started
Call GPT 5.1 Codex Max through AI Gateway with the AI SDK generateText and streamText functions, or through the OpenAI Chat Completions, OpenAI Responses, and Anthropic Messages APIs by changing the base URL. AI Gateway authenticates the request and routes it to an available provider.
Install the AI SDK (pnpm add ai dotenv), create an API key from the API Keys page, and set it as AI_GATEWAY_API_KEY in your environment. Full setup is covered in the text generation quickstart.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'openai/gpt-5.1-codex-max', prompt: 'Why is the sky blue?', });
console.log(result.text);}
main().catch(console.error);Top-level parameters
The same GPT 5.1 Codex Max request in each API format AI Gateway supports.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'openai/gpt-5.1-codex-max', system: 'You are a concise technical assistant.', prompt: 'Summarize the tradeoffs between static generation and SSR.', maxOutputTokens: 1024, });
console.log(result.text);}
main().catch(console.error);Standard parameters like prompt, messages, temperature, and tools work as documented in the AI SDK docs. These are the parameters with model-specific behavior.
| Parameter | Type | Required | Description |
|---|---|---|---|
model | string | Yes | Model ID in the form creator/model, e.g. openai/gpt-5.1-codex-max. AI Gateway routes the request to an available provider. |
maxOutputTokens | number | No | Hard cap on generated tokens. GPT 5.1 Codex Max supports up to 128,000 output tokens. Reasoning tokens count toward this limit. |
reasoning | 'provider-default' | 'none' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh' | No | Provider-agnostic reasoning effort, available in AI SDK 7 or later. Maps to the provider’s native reasoning configuration; reasoning settings under providerOptions take precedence when both are set. See the Reasoning section below. |
providerOptions | Record<string, JSONValue> | No | AI Gateway routing options under gateway, plus any provider-native options under the provider’s own namespace — see the table below. |
Input limits
| Input | Formats | Sources | Max count | Max size | Limits |
|---|---|---|---|---|---|
| Text | — | — | — | — | Prompt and response share the 400K-token context window |
| Image | — | URL, base64, Uint8Array | — | — | Sent as image parts in messages; counts as input tokens |
| — | URL, base64, Uint8Array | — | — | Sent as file parts in messages; counts as input tokens |
Provider options
Set AI Gateway routing options under providerOptions.gateway. For provider-specific options, pass them under the provider’s namespace as documented by the AI SDK.
Learn more in the AI SDK openai provider docs.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'openai/gpt-5.1-codex-max', prompt: 'Why is the sky blue?', providerOptions: { gateway: { only: ['azure'], }, }, });
console.log(result.text);}
main().catch(console.error);These AI Gateway routing options apply to every model. Provider-specific options pass through under the provider’s own namespace (for example providerOptions.anthropic) exactly as documented by the AI SDK.
| Parameter | Type | Required | Description |
|---|---|---|---|
providerOptions.gateway.only | string[] | No | Restrict routing to these provider slugs. Requests fail over only within the listed providers. |
providerOptions.gateway.order | string[] | No | Preferred provider order. Listed providers are tried first; unlisted providers remain available as fallbacks. |
providerOptions.gateway.sort | 'cost' | 'ttft' | 'tps' | No | Rank candidate providers by price, time to first token, or tokens per second instead of the default routing order. |
providerOptions.gateway.zeroDataRetention | boolean | No | Route only to providers with a zero-data-retention policy for this model. |
Routing across providers
AI Gateway serves the same model through multiple providers and fails over automatically. order expresses a preference while keeping every provider eligible; only is a hard allowlist — if none of the listed providers are available the request fails instead of falling back.
Options under a provider's own namespace (for example providerOptions.anthropic) are forwarded to that provider with the request. Providers ignore option namespaces that don't apply to them, so it is safe to set provider options alongside gateway routing options.
Reasoning
AI Gateway bridges reasoning across every API format. The AI SDK exposes a provider-agnostic top-level reasoning level (none, minimal, low, medium, high, or xhigh); the Chat Completions and Responses formats take the same effort under reasoning.effort; and the Anthropic Messages format uses a native thinking token budget. Whichever you send, the gateway maps it to the target model’s native configuration, converting between effort levels and token budgets as needed. Reasoning-related settings under providerOptions take full precedence over the top-level reasoning value and are never merged. Reasoning tokens typically count toward your output-token usage, though how they’re reported and billed varies by provider.
Learn more in the AI Gateway reasoning guide.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'openai/gpt-5.1-codex-max', prompt: 'Explain the Monty Hall problem step by step.', reasoning: 'high', });
console.log(result.text);}
main().catch(console.error);Image input
Send images alongside text as message parts. Images count as input tokens.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'openai/gpt-5.1-codex-max', messages: [ { role: 'user', content: [ { type: 'text', text: 'Describe this image.' }, { type: 'image', image: 'https://example.com/photo.jpg' }, ], }, ], });
console.log(result.text);}
main().catch(console.error);PDF input
Attach PDFs as file parts. Their contents count as input tokens.
import { generateText } from 'ai';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'openai/gpt-5.1-codex-max', messages: [ { role: 'user', content: [ { type: 'text', text: 'Summarize this document.' }, { type: 'file', mediaType: 'application/pdf', data: 'https://example.com/document.pdf', }, ], }, ], });
console.log(result.text);}
main().catch(console.error);Tool calling
Expose tools the model can call. Define each tool’s inputs with a Zod schema.
import { generateText, tool } from 'ai';import { z } from 'zod';import 'dotenv/config';
async function main() { const result = await generateText({ model: 'openai/gpt-5.1-codex-max', prompt: 'What is the weather in San Francisco?', tools: { getWeather: tool({ description: 'Get the current weather for a location', inputSchema: z.object({ location: z.string() }), execute: async ({ location }) => ({ location, temperatureC: 18 }), }), }, });
console.log(result.text);}
main().catch(console.error);Copy link to headingAbout GPT 5.1 Codex Max
GPT 5.1 Codex Max became available on November 19, 2025 on AI Gateway as the premium tier of the GPT-5.1 codex family. It applies the maximum available compute to each request, enabling deeper reasoning and more thorough code analysis than the standard GPT-5.1 codex tier.
The additional compute translates to meaningful quality improvements on the hardest coding tasks: complex architectural decisions, cross-cutting refactors, subtle bug diagnosis, and security analysis where thoroughness is critical. On simpler tasks, the difference from standard codex may be minimal, making selective deployment the most practical pattern.
The model supports the full context window of 400K tokens and operates in the same sandboxed agentic coding environment as other codex variants, reading repositories, writing code, executing tests, and iterating. The difference is in how deeply it reasons about each step.
Copy link to headingWhat To Consider When Choosing a Provider
- Configuration: GPT 5.1 Codex Max is designed for tasks where standard codex models fall short. It applies additional computation to produce more thorough analysis and higher-quality code on genuinely difficult problems.
- Configuration: Most teams use codex max for their hardest tasks (security audits, architectural redesigns, complex migrations) while routing routine work to standard codex or codex mini.
- Zero Data Retention: Zero Data Retention is available for this model. It is offered on a per-provider and model basis. See the documentation for details.
- Authentication: AI Gateway authenticates requests using an API key or OIDC token. You do not need to manage provider credentials directly.
Copy link to headingWhen to Use GPT 5.1 Codex Max
Best for
- Critical security audits: Thorough analysis of codebases for vulnerabilities with maximum reasoning depth
- Large-scale architectural redesigns: Changes that require understanding and restructuring entire systems
- Complex migration projects: Converting between frameworks or architectures with many interdependencies
- Hard debugging: Tracing subtle, cross-cutting bugs that require extensive codebase analysis
- Quality-critical code review: Final review of changes where missed issues have high consequences
Consider alternatives when
- Standard coding tasks: GPT-5.1 codex handles most tasks well at lower cost
- Simple bug fixes: Codex mini is faster and more affordable for routine fixes
- Non-coding analysis: GPT-5.1 thinking for general reasoning tasks
- Speed-sensitive workflows: Any smaller codex variant when response time matters more than depth
Copy link to headingConclusion
GPT 5.1 Codex Max applies maximum compute within the GPT-5.1 codex family to the hardest software engineering challenges. For security audits, architectural redesigns, and other tasks where code quality is paramount, it is the premium tier of the GPT-5.1 codex lineup.
Copy link to headingFrequently Asked Questions
How does GPT 5.1 Codex Max differ from standard GPT-5.1 codex?
It applies more compute per request, enabling deeper reasoning and more thorough analysis. The improvement is most significant on hard problems; simple tasks may not benefit noticeably.
When is the additional cost of codex max justified?
For security audits, large architectural changes, complex migrations, and any task where the consequences of missed issues are high. For routine coding, standard codex is more cost-effective.
What context window does GPT 5.1 Codex Max support?
400K tokens, matching the GPT-5.1 codex family.
How does AI Gateway handle authentication for GPT 5.1 Codex Max?
AI Gateway accepts a single API key or OIDC token for all requests. You don't embed OpenAI credentials in your application; AI Gateway routes and authenticates on your behalf.
Can GPT 5.1 Codex Max verify its own code?
Yes. Like other codex variants, it operates in sandboxed environments where it runs tests and validates output before returning results.
What are typical latency characteristics?
This page shows live throughput and time-to-first-token metrics measured across real AI Gateway traffic. Codex max may take longer due to additional compute applied per request.