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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 modelKimi K2.5MoonshotRemove
ProviderOpenAIMoonshot
Discovery tierBalancedOpen weights
AddedNov 13, 2025Jan 26, 2026
Limits
Context window400KBest262.14K
Max output128KBest65.54K
Average output22 tokens437 tokens
Pricing, USD per 1M tokens
Input$1.25$0.38Best
Output$10.00$2.00Best
Cache read$0.13$0.07Best
Performance
Throughput—91.9 tok/s
Time to first token—1.3 s
Request success (24h)—99.8%
Benchmark indexes
Intelligence Index23.7Best23.5
Coding Index—46.8
Math Index95.7—
Capabilities
ReasoningYesNo
ToolsNoYes
VisionYesYes
Reasoning effort——

Public evaluations

Benchmarks

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

  • GPT 5.1 Codex
  • Kimi K2.5

Intelligence Index

  • GPT 5.1 Codex23.7
  • Kimi K2.523.5

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

  • Coding Index

    Composite of the coding evaluations

    • GPT 5.1 Codex: —
    • Kimi K2.5: 46.8

  • Math Index

    Composite of the math evaluations

    • GPT 5.1 Codex: 95.7
    • Kimi K2.5: —

Agentic work

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • GPT 5.1 Codex: —
    • Kimi K2.5: 839 Elo

Document reasoning

  • AA-LCRv1.1

    Reasoning across long documents

    • GPT 5.1 Codex: 69.3%
    • Kimi K2.5: 78.0%Top

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • GPT 5.1 Codex: 25.7%
    • Kimi K2.5: 30.7%Top

  • GPQA Diamond

    Graduate-level science questions

    • GPT 5.1 Codex: 86.0%
    • Kimi K2.5: 87.9%Top

  • MMLU-Pro

    Multi-subject knowledge and reasoning

    • GPT 5.1 Codex: 86.0%
    • Kimi K2.5: —

  • IFBench

    Following precise output instructions

    • GPT 5.1 Codex: 70.0%
    • Kimi K2.5: 70.2%Top

Coding

  • LiveCodeBench

    Recent competitive programming problems

    • GPT 5.1 Codex: 84.9%
    • Kimi K2.5: —

Math

  • AIME 2025

    Competition mathematics, 2025 problems

    • GPT 5.1 Codex: 95.7%
    • Kimi K2.5: —

Legacy evaluations

  • Terminal-Bench Hard

    Earlier terminal task suite

    • GPT 5.1 Codex: 34.8%Top
    • Kimi K2.5: 34.8%Top

  • τ²-Bench Telecom

    Tool use in a customer-support simulation

    • GPT 5.1 Codex: 83.0%
    • Kimi K2.5: 95.9%Top

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • GPT 5.1 Codex: 69.3%
    • Kimi K2.5: 78.0%Top

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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