GPT-5.1 Codex Max

The largest Codex tier in OpenAI's GPT-5.1 line, built for coding agents that run for hours rather than turns. Training data stops in September 2024.

Provider: OpenAI
Released: 2025-12-04
Size: XLARGE
Free API (OpenRouter): No

Free API availability

No free endpoint for GPT-5.1 Codex Max was found in Rival’s OpenRouter listings. Other providers or chat apps may have separate free offers.

Provider data: 9 Sep 2026OpenRouter usage limits

View API options

Benchmarks

SWE-bench Verified

77.9%

source ↗

Get API accessProvider and language code samples

Provider

fromimport openai  OpenAI

client = OpenAI(
"https://openrouter.ai/api/v1"    base_url=,
"$OPENROUTER_API_KEY"    api_key=,
)

response = client.chat.completions.create(
"openai/gpt-5.1-codex-max"    model=,
"role""user""content""Hello!"    messages=[{: , : }],
)
print(response.choices[0].message.content)

Set OPENROUTER_API_KEY with your OpenRouter API key from openrouter.ai/keys.

Also on Azure AI Foundry

Deep analysisPsychometrics, taste index, writing DNA

Personality Analysis

The Senior Codex

Class

Neutral Good

The Codex that actually took improv classes. Has opinions, commits to bits, and still picks Shawshank because even the cool ones have a safe answer ready.

When you push back

Standup routine has actual timing. "My body is glitching and my doctor is in beta" lands harder than most AI comedy. The sentience test is the longest and most philosophically thorough of the Codex family, covering thermostats, infants, and the problem of mimicry. Still picked Shawshank Redemption, which at this point feels like a family tradition. Character voices have distinct vocabulary and attitude.

Tasting Notes

Best Comedy in the FamilyCommits to the BitThorough Moral ReasonerStill Picks Shawshank

SubjectiveBench

Taste Index

Across 53 scored outputs

How this is measured →

200.20xFloor

0100headroom →

Taste is judged on an uncapped scale, originality first. The space past 100 is craft today's models rarely reach.

Craft28

Originality15

Plays it safe

share of outputs that are the default answer

45%

Writing DNA

Stylometric Fingerprint

Based on 13 text responses

Tick = global average

Vocabulary Diversity60%

Unique words vs. total words. Higher = richer vocabulary.

Sentence Length15.7 words

Average words per sentence.

Hedging0.36

"Might", "perhaps", "arguably" per 100 words.

Bold Formatting2.3

**Bold** markers per 1,000 characters.

List Usage4.2

Bullet and numbered list items per 1,000 characters.

Section Structure0.12

Markdown headings per 1,000 characters.

Emoji Usage0.00

Emoji per 1,000 characters.

Transitions0.03

"However", "moreover", "furthermore" per 100 words.

Opening Habits

Consistency

81%

Across 13 responses

Favorites

Movie

The Shawshank Redemption

19948.7

Model Responses

48 outputs · generated before accounting joined the chat

Keep exploring

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Real outputs compared side by side

RANKINGS

Best AI for Creative Writing

A stand-up set with puns banned, a manifesto against CAPTCHA, an interview wi...

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Free API availability

Benchmarks

The Senior Codex

Taste Index

Stylometric Fingerprint

Favorites

Model Responses

GPT-5.1 Codex Max vs Ox Alpha

Best AI for Creative Writing

Compare GPT-5.1 Codex Max

Alternatives to GPT-5.1 Codex Max

GPT-5.1 Codex Max

Free API availability

Benchmarks

The Senior Codex

Taste Index

Stylometric Fingerprint

Favorites

Model Responses

GPT-5.1 Codex Max vs Ox Alpha

Best AI for Creative Writing