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OpenAI · Frontier

GPT 5.3 Codex

Added Feb 24, 2026

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Use in the app

Coding-focused GPT-5.3 variant with optimized routing.

  • Reasoning
  • Tools
  • Vision
  • Structured output
  • PDF input
Input
Text, Images
Output
Text
Reasoning effort
low · medium · high · xhigh
Discovery tier
Frontier

Pricing

USD per 1M tokens
Input
$1.75
Output
$14.00
Cache read
$0.18

Reference prices as published by the model provider. API example

Specifications

Context window
400K
Max output
128K
Average output (7 days)
281 tokens
Longer than 29% of 473 models

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TryGemini 3.5 FlashClaude 4.6 Opus ThinkingMuse Spark 1.1All 3

Public evaluations

Benchmarks

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

Intelligence Index

32.5

Tested at xhigh reasoning effort

Better than 76% of 326 scored models

3.8Catalog models by score55.1

Agentic work

  • AA-Briefcasev1.1

    868 Elo

    Agentic knowledge work, rated head to head

    Better than 36% of 166 scored models

Document reasoning

  • AA-LCRv1.1

    83.3%

    Reasoning across long documents

    Better than 92% of 309 scored models

Reasoning and knowledge

  • Humanity’s Last Exam

    42.5%

    Expert-level questions across academic fields

    Better than 84% of 323 scored models

  • GPQA Diamond

    91.5%

    Graduate-level science questions

    Better than 85% of 291 scored models

  • IFBench

    75.4%

    Following precise output instructions

    Better than 83% of 215 scored models

Legacy evaluations

  • Terminal-Bench Hard

    53.0%

    Earlier terminal task suite

    Better than 92% of 212 scored models

  • τ²-Bench Telecom

    86.0%

    Tool use in a customer-support simulation

    Better than 70% of 214 scored models

  • AA-LCR (unversioned)

    83.3%

    Long-context reasoning, earlier grading

    Better than 92% of 309 scored models

Scores from Artificial Analysis, updated Oct 26, 2026. GPT 5.3 Codex was tested at xhigh reasoning effort; compare scores measured at the same effort.Artificial Analysis

Live routing data

Performance and reliability

Recent averages across requests routed for this model. Your own speed depends on prompt length, reasoning effort and load.

Prompt cache hits
82.3%
About $0.45 per 1M input tokens with caching
Request success (24h)
98.5%
Reliable

Cache hits are the share of input tokens recently served from a prompt cache across all requests. They are not a forecast of your own hit rate.

Hourly request success · last 72 hoursLowest hour 97.4%
  • Healthy (98% or more)
  • Degraded (90–98%)
  • Down (under 90%)
  • No requests

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-5.3-codex",
    "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-5.3-codex",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

OpenAI

Other OpenAI models, starting with the same family.