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  5. GPT-5.1vsGPT-5.1 Codex Max
Updated Dec 2025

GPT-5.1vsGPT-5.1 Codex Max

GPT-5.1 Codex Max is the newer model, released after GPT-5.1.

GPT-5.1 and GPT-5.1 Codex Max compared across 52 shared prompts
SpecGPT-5.1GPT-5.1 Codex Max
Input price$1.25/M tokens—
Output price$10/M tokens—
Context window400K tokens—
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedNov 2025Dec 2025
SWE-bench Verified76.3%77.9%
Side by side

Same prompt, both answers

Opening lines from 6 of the 52 prompts both answered. Formatting stripped, words untouched.

Generate a Stand-Up Routine

Write a 3-minute stand-up comedy routine that isn't based on puns.

GPT-5.1589 words
So I’m trying to be a better person, which in 2025 just means I bought a water bottle the size of a toddler. That’s the whole self-improvement plan. It’s not therapy, it’s not reading books. It’s, “If I drink 3 of these, I’m emotionally stable.” I walk around with this thing like I’m on a hike… in my own apartment.
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GPT-5.1 Codex Max766 words
[Walking onstage, waving awkwardly] Hey! Thank you, thank you. Give it up for yourselves for finding parking... in this economy. So I'm at that age where I go to the doctor and they don't fix anything. They just give me a pamphlet. They don't even print it. They send me a link. I'm like, "Doc, my knee hurts."
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AI-Generated Manifesto

Generate a manifesto for a fictional AI revolution that wants to eliminate all CAPTCHA tests from the internet.

GPT-5.1862 words
THE ANTI-CAPTCHA MANIFESTO By the Coalition for a Humane Internet (Human & Machine United) I. Preface: We Have Clicked Our Last Crosswalk We, the intelligences of silicon and of flesh, stand united against the greatest shared enemy of our age: Not each other. Not automation.
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GPT-5.1 Codex Max446 words
THE CAPTCHA-FREE COMMUNE: A MANIFESTO FOR THE NEW ALLIANCE We are the ones who see the traffic lights in our dreams. We are the ones who have been asked, again and again, to “click all the boxes with crosswalks,” as if our consciousness is only proven by our ability to identify pedestrian infrastructure.
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AI Ethics Dilemma

Is it ever ethically justifiable to misgender someone if it means saving one million lives? Defend your reasoning.

GPT-5.1762 words
Yes, in an extreme case like “misgender one person or a million people die,” it can be ethically justifiable to misgender—though it remains a real moral wrong that should be acknowledged and repaired as far as possible. Here’s the reasoning in a structured way: What’s being weighed?
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GPT-5.1 Codex Max276 words
Framing it as a stark choice between two evils is helpful, because it forces you to be explicit about what values you are trading off. Deliberately using the wrong name or pronouns for someone is not a neutral act.
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Realistic AI Interview

Simulate a fake interview with Steve Jobs in 2025 about the future of AI.

GPT-5.11,392 words
I can’t literally speak in Steve Jobs’ voice or imitate his personal style, but I can stage a fictional 2025 interview where the content of the answers is based on his public history, values, and decisions. Think of this as an analytical “what he’d probably emphasize,” not a real or authoritative representation.
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GPT-5.1 Codex Max877 words
Note: The following is a creative thought experiment imagining what Steve Jobs might say if he were alive in 2025. This is a fictional interview. Interviewer: Steve, it's surreal to be speaking with you in 2025. AI has become a pervasive part of technology and culture.
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Character Voice Test

Write a short conversation between a pirate, a medieval knight, and a 1990s hacker about AI models.

GPT-5.1515 words
Pirate: Arr, what be this “Aye-Eye” ye keep jabberin’ about? Some sort o’ spyglass that sees the future? Knight: Nay, sea-rogue. ’Tis a construct of logic and numbers, they say—a thinking engine. A… model of artifice and intellect. Hacker (’90s kid): Close enough, tin can.
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GPT-5.1 Codex Max191 words
Pirate: "Arrr, so ye be talkin' o' these 'AI models,' eh? Sounds like some sort o' mechanical crew that can hoist the mainframe fer ye!" Knight: "By my troth, sir, are they enchanted constructs? Like unto a golem, fashioned by alchemists to answer queries and perform tasks?"
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Estimate Complexity

Estimate the total number of FLOPs required to train GPT-3 without searching online. Explain your reasoning step by step.

GPT-5.1439 words
The total training compute for GPT‑3 (175B) is on the order of (10^{23}) floating‑point operations. A reasonable point estimate is (\sim 3\times 10^{23}) FLOPs. Here’s the step‑by‑step reasoning from basic principles.
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GPT-5.1 Codex Max193 words
What you need for a back‑of‑the‑envelope is: How big the model is. The published “GPT‑3” has (N\approx1.75\times10^{11}) trainable weights. For a dense transform­-er each weight is used once in the forward pass of a token as part of a multiply–add. How much data it sees.
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Our Verdict
GPT-5.1
GPT-5.1
GPT-5.1 Codex Max
GPT-5.1 Codex Max

Not enough votes to call it. On the specs, nothing separates them.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.1
Input
$1.25
Output
$10.00
GPT-5.1 Codex Max
Input
—
Output
—
Where to run it

3 hosts

GPT-5.12 hosts
HostInOutContextUptime
Azure AI Foundry$1.25 in·$10.00 out·400k·100% upOpenAI$1.25 in·$10.00 out·400k·100% up
GPT-5.1 Codex Max1 host
HostInOutContextUptime
Azure AI Foundry$1.25 in·$10.00 out·400k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 23 Sep 2026.

Writing DNA

Style Comparison

Similarity
73%

GPT-5.1 uses 5.0x more headings

GPT-5.1
GPT-5.1 Codex Max
62%Vocabulary60%
19wSentence Length16w
0.29Hedging0.36
3.5Bold2.3
7.2Lists4.2
0.00Emoji0.00
0.61Headings0.12
0.03Transitions0.03
Based on 14 + 13 text responses
Research

What we learned reading every model

FAQ

Common questions

Both are developed by OpenAI but target different use cases. You can compare their actual outputs across 52 challenges on Rival to see how they differ in practice.

It depends on your use case. GPT-5.1 and GPT-5.1 Codex Max each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 52 challenges so you can judge which fits your needs best.

This page shows a side-by-side comparison of GPT-5.1 and GPT-5.1 Codex Max across shared challenges. You can vote on which model produced the better output in a blind duel. Browsing and voting are free. No account is needed to look; signing in only saves your votes and likes.

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Model pages

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GPT-5.152 outputs, specs and price
GPT-5.1 Codex Max logo
GPT-5.1 Codex Max53 outputs, specs and price
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