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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 LunaOpenAIRemove
ProviderOpenAIOpenAI
Discovery tierFrontierEfficient
AddedDec 4, 2025Sep 22, 2026
Limits
Context window400K1.05MBest
Max output128K128K
Average output—120 tokens
Pricing, USD per 1M tokens
Input$2.50$0.10Best
Output$20.00$0.50Best
Cache read$0.25$0.01Best
Cache write—$0.13
Performance
Throughput—77.0 tok/s
Time to first token—6.8 s
Request success (24h)—99.8%
Benchmark indexes
Intelligence Index23.729.9Best
Math Index95.7—
Capabilities
ReasoningYesYes
ToolsYesYes
VisionYesYes
Structured outputYesYes
PDF inputYesYes
Reasoning effortnone, minimal, low, medium, high, xhighnone, low, 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 Luna

Intelligence Index

  • GPT 5.1 Codex Max23.7
  • GPT 6 Luna29.9

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 Luna: —

Agentic work

  • AutomationBench-AA

    Workflow automation, penalized for guardrail violations

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 40.5%

  • AutomationBench-AA tasks completed

    Workflows finished end to end without a guardrail violation

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 10.2%

  • AA-Briefcasev1.1

    Agentic knowledge work, rated head to head

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 1,097 Elo

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 1,263 Elo

Document reasoning

  • GDP.pdf

    Professional reasoning over PDF documents, all-pass rate

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 13.8%

  • AA-LCRv1.1

    Reasoning across long documents

    • GPT 5.1 Codex Max: 69.3%
    • GPT 6 Luna: 78.3%Top

  • MLCR-AA

    Long-context reasoning over medical records

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 18.3%

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • GPT 5.1 Codex Max: 25.7%
    • GPT 6 Luna: 28.3%Top

  • GPQA Diamond

    Graduate-level science questions

    • GPT 5.1 Codex Max: 86.0%
    • GPT 6 Luna: —

  • MMLU-Pro

    Multi-subject knowledge and reasoning

    • GPT 5.1 Codex Max: 86.0%
    • GPT 6 Luna: —

  • IFBench

    Following precise output instructions

    • GPT 5.1 Codex Max: 70.0%
    • GPT 6 Luna: —

Coding

  • Terminal-Benchv4.0

    Practical software engineering in a terminal

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 2.5%

  • SciCode

    Scientific computing in Python

    • GPT 5.1 Codex Max: —
    • GPT 6 Luna: 50.9%

  • LiveCodeBench

    Recent competitive programming problems

    • GPT 5.1 Codex Max: 84.9%
    • GPT 6 Luna: —

Math

  • AIME 2025

    Competition mathematics, 2025 problems

    • GPT 5.1 Codex Max: 95.7%
    • GPT 6 Luna: —

Legacy evaluations

  • Terminal-Bench Hard

    Earlier terminal task suite

    • GPT 5.1 Codex Max: 34.8%
    • GPT 6 Luna: —

  • τ²-Bench Telecom

    Tool use in a customer-support simulation

    • GPT 5.1 Codex Max: 83.0%
    • GPT 6 Luna: —

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • GPT 5.1 Codex Max: 69.3%
    • GPT 6 Luna: 78.3%Top

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.