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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

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Public evaluations

Benchmarks

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

Intelligence Index

23.7

Tested at high reasoning effort

Better than 58% of 326 scored models

3.8Catalog models by score55.1

Indexes

  • Math Index

    95.7

    Composite of the math evaluations

    Better than 98% of 118 scored models

Document reasoning

  • AA-LCRv1.1

    69.3%

    Reasoning across long documents

    Better than 48% of 309 scored models

Reasoning and knowledge

  • Humanity’s Last Exam

    25.7%

    Expert-level questions across academic fields

    Better than 56% of 323 scored models

  • GPQA Diamond

    86.0%

    Graduate-level science questions

    Better than 64% of 291 scored models

  • MMLU-Pro

    86.0%

    Multi-subject knowledge and reasoning

    Better than 90% of 132 scored models

  • IFBench

    70.0%

    Following precise output instructions

    Better than 71% of 215 scored models

Coding

  • LiveCodeBench

    84.9%

    Recent competitive programming problems

    Better than 92% of 129 scored models

Math

  • AIME 2025

    95.7%

    Competition mathematics, 2025 problems

    Better than 98% of 118 scored models

Legacy evaluations

  • Terminal-Bench Hard

    34.8%

    Earlier terminal task suite

    Better than 66% of 212 scored models

  • τ²-Bench Telecom

    83.0%

    Tool use in a customer-support simulation

    Better than 62% of 214 scored models

  • AA-LCR (unversioned)

    69.3%

    Long-context reasoning, earlier grading

    Better than 48% of 309 scored models

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

Other OpenAI models, starting with the same family.