OpenAI · Balanced
GPT 5.1 Codex
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.
| GPT 5.1 CodexOpenAIThis model | GPT 6 Luna ProOpenAIRemove | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Discovery tier | Balanced | Efficient |
| Added | Nov 13, 2025 | Sep 22, 2026 |
| Limits | ||
| Context window | 400K | 1.05MBest |
| Max output | 128K | 128K |
| Average output | 22 tokens | 2.8K tokens |
| Pricing, USD per 1M tokens | ||
| Input | $1.25 | $0.10Best |
| Output | $10.00 | $0.50Best |
| Cache read | $0.13 | $0.01Best |
| Cache write | — | $0.13 |
| Performance | ||
| Throughput | — | 245.6 tok/s |
| Time to first token | — | 22.2 s |
| Request success (24h) | — | 100.0% |
| Benchmark indexes | ||
| Intelligence Index | 23.7 | — |
| Math Index | 95.7 | — |
| Capabilities | ||
| Reasoning | Yes | Yes |
| Tools | No | Yes |
| Vision | Yes | Yes |
| Structured output | No | Yes |
| PDF input | No | Yes |
| 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 Luna Pro
Intelligence Index
- GPT 5.1 Codex23.7
- GPT 6 Luna Pro—
GPT 5.1 Codex tested at high reasoning effort
GPT 5.1 Codex: Better than 58% of 326 scored models
Indexes
Math Index
Composite of the math evaluations
- GPT 5.1 Codex: 95.7
- GPT 6 Luna Pro: —
Document reasoning
AA-LCRv1.1
Reasoning across long documents
- GPT 5.1 Codex: 69.3%
- GPT 6 Luna Pro: —
Reasoning and knowledge
Humanity’s Last Exam
Expert-level questions across academic fields
- GPT 5.1 Codex: 25.7%
- GPT 6 Luna Pro: —
GPQA Diamond
Graduate-level science questions
- GPT 5.1 Codex: 86.0%
- GPT 6 Luna Pro: —
MMLU-Pro
Multi-subject knowledge and reasoning
- GPT 5.1 Codex: 86.0%
- GPT 6 Luna Pro: —
IFBench
Following precise output instructions
- GPT 5.1 Codex: 70.0%
- GPT 6 Luna Pro: —
Coding
LiveCodeBench
Recent competitive programming problems
- GPT 5.1 Codex: 84.9%
- GPT 6 Luna Pro: —
Math
AIME 2025
Competition mathematics, 2025 problems
- GPT 5.1 Codex: 95.7%
- GPT 6 Luna Pro: —
Legacy evaluations
Terminal-Bench Hard
Earlier terminal task suite
- GPT 5.1 Codex: 34.8%
- GPT 6 Luna Pro: —
τ²-Bench Telecom
Tool use in a customer-support simulation
- GPT 5.1 Codex: 83.0%
- GPT 6 Luna Pro: —
AA-LCR (unversioned)
Long-context reasoning, earlier grading
- GPT 5.1 Codex: 69.3%
- GPT 6 Luna 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.
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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