OpenAI · Frontier
GPT 5.3 Codex
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 465 models
Side by side
GPT 5.3 Codex compared
Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.
| GPT 5.3 CodexOpenAIThis model | GPT 6 Luna ProOpenAIRemove | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Discovery tier | Frontier | Efficient |
| Added | Feb 24, 2026 | Sep 22, 2026 |
| Limits | ||
| Context window | 400K | 1.05MBest |
| Max output | 128K | 128K |
| Average output | 281 tokens | 2.8K tokens |
| Pricing, USD per 1M tokens | ||
| Input | $1.75 | $0.10Best |
| Output | $14.00 | $0.50Best |
| Cache read | $0.18 | $0.01Best |
| Cache write | — | $0.13 |
| Performance | ||
| Throughput | — | 245.6 tok/s |
| Time to first token | — | 22.2 s |
| Request success (24h) | 98.5% | 100.0%Best |
| Benchmark indexes | ||
| Intelligence Index | 32.5 | — |
| Capabilities | ||
| Reasoning | Yes | Yes |
| Tools | Yes | Yes |
| Vision | Yes | Yes |
| Structured output | Yes | Yes |
| PDF input | Yes | Yes |
| Reasoning effort | low, medium, high, xhigh | low, medium, high, xhigh, max |
Public evaluations
Benchmarks
Independent evaluation results, with how each score ranks among the models in the Noumen catalog.
- GPT 5.3 Codex
- GPT 6 Luna Pro
Intelligence Index
- GPT 5.3 Codex32.5
- GPT 6 Luna Pro—
GPT 5.3 Codex tested at xhigh reasoning effort
GPT 5.3 Codex: Better than 76% of 326 scored models
Agentic work
AA-Briefcasev1.1
Agentic knowledge work, rated head to head
- GPT 5.3 Codex: 868 Elo
- GPT 6 Luna Pro: —
Document reasoning
AA-LCRv1.1
Reasoning across long documents
- GPT 5.3 Codex: 83.3%
- GPT 6 Luna Pro: —
Reasoning and knowledge
Humanity’s Last Exam
Expert-level questions across academic fields
- GPT 5.3 Codex: 42.5%
- GPT 6 Luna Pro: —
GPQA Diamond
Graduate-level science questions
- GPT 5.3 Codex: 91.5%
- GPT 6 Luna Pro: —
IFBench
Following precise output instructions
- GPT 5.3 Codex: 75.4%
- GPT 6 Luna Pro: —
Legacy evaluations
Terminal-Bench Hard
Earlier terminal task suite
- GPT 5.3 Codex: 53.0%
- GPT 6 Luna Pro: —
τ²-Bench Telecom
Tool use in a customer-support simulation
- GPT 5.3 Codex: 86.0%
- GPT 6 Luna Pro: —
AA-LCR (unversioned)
Long-context reasoning, earlier grading
- GPT 5.3 Codex: 83.3%
- GPT 6 Luna Pro: —
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
- 7.7%
- About $1.63 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.
- 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.
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
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