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OpenAI · Balanced

GPT 5.1 Codex

Added Nov 13, 2025

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Use in the app

Coding-focused GPT-5.1 variant with optimized routing.

  • Reasoning
  • Vision
Input
Text, Images
Output
Text
Discovery tier
Balanced

Pricing

USD per 1M tokens
Input
$1.25
Output
$10.00
Cache read
$0.13

Reference prices as published by the model provider. API example

Specifications

Context window
400K
Max output
128K
Average output (7 days)
22 tokens
Longer than 0% of 465 models

Side by side

GPT 5.1 Codex 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 CodexOpenAIThis modelGPT 6.1 Sol ProOpenAIRemove
ProviderOpenAIOpenAI
Discovery tierBalancedFrontier
AddedNov 13, 2025Sep 29, 2026
Limits
Context window400K1.05MBest
Max output128K128K
Average output22 tokens1.2K tokens
Pricing, USD per 1M tokens
Input$1.25Best$2.00
Output$10.00$10.00
Cache read$0.13$0.10Best
Cache write—$2.50
Performance
Request success (24h)—100.0%
Benchmark indexes
Intelligence Index23.7—
Math Index95.7—
Capabilities
ReasoningYesYes
ToolsNoYes
VisionYesYes
Structured outputNoYes
PDF inputNoYes
Reasoning effort—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
  • GPT 6.1 Sol Pro

Intelligence Index

  • GPT 5.1 Codex23.7
  • GPT 6.1 Sol Pro—

GPT 5.1 Codex tested at high reasoning effort

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

Document reasoning

  • AA-LCRv1.1

    Reasoning across long documents

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

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

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

  • GPQA Diamond

    Graduate-level science questions

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

  • MMLU-Pro

    Multi-subject knowledge and reasoning

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

  • IFBench

    Following precise output instructions

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

Coding

  • LiveCodeBench

    Recent competitive programming problems

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

Math

  • AIME 2025

    Competition mathematics, 2025 problems

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

Legacy evaluations

  • Terminal-Bench Hard

    Earlier terminal task suite

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

  • τ²-Bench Telecom

    Tool use in a customer-support simulation

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

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

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

Scores from Artificial Analysis, updated Oct 26, 2026. GPT 5.1 Codex 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",
    "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",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

OpenAI

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