What is GPT-5.1 Codex Max?

GPT-5.1 Codex Max is a high-accuracy coding model designed for large codebases, migrations, and long-horizon agentic coding with extended autonomous operation.

How good is GPT-5.1 Codex Max?

It achieves 77.9% accuracy on SWE-bench Verified (up from 73.7%) while using 30% fewer thinking tokens. It can operate independently for hours or even days.

What can GPT-5.1 Codex Max do?

It excels at complex long-horizon agentic coding, large-scale refactoring, deep debugging sessions, and tasks requiring extended autonomous operation.

How much does GPT-5.1 Codex Max cost?

GPT-5.1 Codex Max pricing is $1.25 per 1M input tokens and $10.00 per 1M output tokens. Cached input tokens cost $0.125 per 1M.

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GPT-5.1 Codex Max

High-accuracy Codex for large codebases and migrations.

Try in Playground

Community Sentiment

Mixed

Based on Reddit reviews

Community Verdict

Best for Agentic Coding

Based on Reddit reviews

Input Modalities

Text, Images

Output Modalities

Text

Price / 1M tokens

$1.25$10

InputOutput

Best For

Complex, long-run agentic coding (24+ hrs)

Large-scale refactors (millions of tokens)

Deep debugging with long context

Tasks needing very high reasoning

Projects requiring memory compaction

77.9% SWE-bench using 30% fewer tokens

Avoid For

Strict guardrail needs (ignores read-only modes)

Tasks where file changes must be avoided

Workflows needing reliable, uninterrupted runs

Cost-sensitive use

Simple coding (use Codex Mini)

200,000 context window

100,000 max output tokens

Jan 1, 2024 knowledge cutoff

Reasoning supported

Parameters

While OpenAI documents a unified parameter set for the Chat Completions and Responses APIs, each model supports only a limited subset of model-specific parameters and values. This table lists the supported model-specific GPT-5.1 Codex Max API parameters and allowed values.

Parameter	Description	Path	Supported Values
Model	Selects the model version for the request	model	gpt-5.1-codex-max
Message roles	Defines the role of the message in the input	messages[].role	developersystemuserassistant
Reasoning effort	Controls the depth of internal reasoning used by the model	reasoning_effort	lowmediumhighxhigh
Reasoning summary	Controls whether the model produces a concise or detailed reasoning summary	reasoning_summary	detailedauto
Max output tokens	Max output tokens the model may generate	max_completion_tokens	16 .. 100,000
Verbosity	Controls how brief or detailed the generated response is	verbosity	medium
Output format	Specifies the output format, including structured JSON schemas	response_format	textjson_objectjson_schema
Temperature	Controls how random or deterministic the output is	temperature	Not supported
Top P	Controls how diverse the output tokens are	top_p	Not supported
Presence penalty	Encourages the model to introduce new topics	presence_penalty	Not supported
Frequency penalty	Reduces repetition of the same words or phrases	frequency_penalty	Not supported

Pricing

GPT-5.1 Codex Max API pricing is based on token usage for input and output. Prices are listed per 1M tokens, with lower rates for cached input. Tool-specific features may add per-call fees.

Text tokens

Per 1M tokens

Input$1.25

Cached input$0.13

Output$10.00

Example costs (GPT-5.1 Codex Max)

TASK

APPROX COST

Large codebase analysis (100k tokens)

~$0.12

Multi-file refactoring session

~$0.50–$2.00

24-hour autonomous coding run

~$5.00–$20.00

Modalities

What the model can accept and produce

TextInput and output

ImagesInput only

AudioNot supported

VideoNot supported

Features

Platform-level capabilities

StreamingSupported

Function callingSupported

Structured outputsSupported

Fine-tuningNot supported

DistillationNot supported

Predicted outputsNot supported

Tools

Tools supported by this model when using the Responses API.

Web searchSupported

File searchSupported

Image generationNot supported

Code interpreterSupported

MCPSupported

Computer useNot supported

Snapshots

GPT-5.1 Codex Max model snapshots ensure stable behavior by locking a specific version. See all available snapshots and aliases below.

gpt-5.1-codex-max

↪ gpt-5.1-codex-max

gpt-5.1-codex-max

FAQs

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