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 | Claude 4.6 Opus ThinkingAnthropicRemove | |
|---|---|---|
| Provider | OpenAI | Anthropic |
| Discovery tier | Frontier | Frontier |
| Added | Feb 24, 2026 | Feb 5, 2026 |
| Limits | ||
| Context window | 400K | 1MBest |
| Max output | 128K | 128K |
| Average output | 281 tokens | 1.4K tokens |
| Pricing, USD per 1M tokens | ||
| Input | $1.75Best | $5.00 |
| Output | $14.00Best | $25.00 |
| Cache read | $0.18Best | $0.50 |
| Performance | ||
| Throughput | — | 77.0 tok/s |
| Time to first token | — | 1.9 s |
| Request success (24h) | 98.5% | 100.0%Best |
| Benchmark indexes | ||
| Intelligence Index | 32.5Best | 31.9 |
| 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
- Claude 4.6 Opus Thinking
Intelligence Index
- GPT 5.3 Codex32.5
- Claude 4.6 Opus Thinking31.9
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
- Claude 4.6 Opus Thinking: —
Document reasoning
AA-LCRv1.1
Reasoning across long documents
- GPT 5.3 Codex: 83.3%Top
- Claude 4.6 Opus Thinking: 78.0%
Reasoning and knowledge
Humanity’s Last Exam
Expert-level questions across academic fields
- GPT 5.3 Codex: 42.5%Top
- Claude 4.6 Opus Thinking: 39.9%
GPQA Diamond
Graduate-level science questions
- GPT 5.3 Codex: 91.5%Top
- Claude 4.6 Opus Thinking: 89.6%
IFBench
Following precise output instructions
- GPT 5.3 Codex: 75.4%Top
- Claude 4.6 Opus Thinking: 53.1%
Legacy evaluations
Terminal-Bench Hard
Earlier terminal task suite
- GPT 5.3 Codex: 53.0%Top
- Claude 4.6 Opus Thinking: 46.2%
τ²-Bench Telecom
Tool use in a customer-support simulation
- GPT 5.3 Codex: 86.0%
- Claude 4.6 Opus Thinking: 92.1%Top
AA-LCR (unversioned)
Long-context reasoning, earlier grading
- GPT 5.3 Codex: 83.3%Top
- Claude 4.6 Opus Thinking: 78.0%
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
- GPT 5.3 Codex
- Claude 4.6 Opus Thinking
| Leaderboard | GPT 5.3 Codex | Claude 4.6 Opus Thinking |
|---|---|---|
| ASCII Art | Not in top 20 | #14 · 1252 |
Ranks among Noumen catalog models on Design Arena leaderboards. Only top-20 placements are listed.Design Arena
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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