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OpenAI · Frontier

GPT 5.1 Codex Max

Added Dec 4, 2025

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Use in the app

Top-tier GPT-5.1 Codex route used when direct OpenAI is unavailable.

  • Reasoning
  • Tools
  • Vision
  • Structured output
  • PDF input
Input
Text, Images
Output
Text
Reasoning effort
none · minimal · low · medium · high · xhigh
Discovery tier
Frontier

Pricing

USD per 1M tokens
Input
$2.50
Output
$20.00
Cache read
$0.25

Reference prices as published by the model provider. API example

Specifications

Context window
400K
Max output
128K

Side by side

GPT 5.1 Codex Max compared

Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.

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GPT 5.1 Codex MaxOpenAIThis modelGPT 6.1 Sol ProOpenAIRemove
ProviderOpenAIOpenAI
Discovery tierFrontierFrontier
AddedDec 4, 2025Sep 29, 2026
Limits
Context window400K1.05MBest
Max output128K128K
Average output—1.2K tokens
Pricing, USD per 1M tokens
Input$2.50$2.00Best
Output$20.00$10.00Best
Cache read$0.25$0.10Best
Cache write—$2.50
Performance
Request success (24h)—100.0%
Benchmark indexes
Intelligence Index23.7—
Math Index95.7—
Capabilities
ReasoningYesYes
ToolsYesYes
VisionYesYes
Structured outputYesYes
PDF inputYesYes
Reasoning effortnone, minimal, low, medium, high, xhighlow, medium, high, xhigh, max

Public evaluations

Benchmarks

Independent evaluation results, with how each score ranks among the models in the Noumen catalog.

  • GPT 5.1 Codex Max
  • GPT 6.1 Sol Pro

Intelligence Index

  • GPT 5.1 Codex Max23.7
  • GPT 6.1 Sol Pro—

GPT 5.1 Codex Max tested at high reasoning effort

GPT 5.1 Codex Max: Better than 58% of 326 scored models

3.8Catalog models by score55.1

Indexes

  • Math Index

    Composite of the math evaluations

    • GPT 5.1 Codex Max: 95.7
    • GPT 6.1 Sol Pro: —

Document reasoning

  • AA-LCRv1.1

    Reasoning across long documents

    • GPT 5.1 Codex Max: 69.3%
    • GPT 6.1 Sol Pro: —

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • GPT 5.1 Codex Max: 25.7%
    • GPT 6.1 Sol Pro: —

  • GPQA Diamond

    Graduate-level science questions

    • GPT 5.1 Codex Max: 86.0%
    • GPT 6.1 Sol Pro: —

  • MMLU-Pro

    Multi-subject knowledge and reasoning

    • GPT 5.1 Codex Max: 86.0%
    • GPT 6.1 Sol Pro: —

  • IFBench

    Following precise output instructions

    • GPT 5.1 Codex Max: 70.0%
    • GPT 6.1 Sol Pro: —

Coding

  • LiveCodeBench

    Recent competitive programming problems

    • GPT 5.1 Codex Max: 84.9%
    • GPT 6.1 Sol Pro: —

Math

  • AIME 2025

    Competition mathematics, 2025 problems

    • GPT 5.1 Codex Max: 95.7%
    • GPT 6.1 Sol Pro: —

Legacy evaluations

  • Terminal-Bench Hard

    Earlier terminal task suite

    • GPT 5.1 Codex Max: 34.8%
    • GPT 6.1 Sol Pro: —

  • τ²-Bench Telecom

    Tool use in a customer-support simulation

    • GPT 5.1 Codex Max: 83.0%
    • GPT 6.1 Sol Pro: —

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • GPT 5.1 Codex Max: 69.3%
    • GPT 6.1 Sol Pro: —

Scores from Artificial Analysis, updated Oct 26, 2026. GPT 5.1 Codex Max was tested at high reasoning effort; compare scores measured at the same effort.Artificial Analysis

Developers

Use it through the API

Noumen’s API is OpenAI-compatible: any Chat Completions client works with a base URL and a key.

Read the quickstart
curl https://www.noumen.xyz/api/v1/chat/completions \
  -H "Authorization: Bearer $NOUMEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.1-codex-max",
    "reasoning_effort": "medium",
    "messages": [{ "role": "user", "content": "Explain this stack trace." }]
  }'
import os
from openai import OpenAI

client = OpenAI(base_url="https://www.noumen.xyz/api/v1", api_key=os.environ["NOUMEN_API_KEY"])
reply = client.chat.completions.create(
    model="openai/gpt-5.1-codex-max",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

OpenAI

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