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  5. Claude Fable 5vsGPT-5.1 Codex Max
Updated Jun 2026

Claude Fable 5vsGPT-5.1 Codex Max

Claude Fable 5 is the newer model, released after GPT-5.1 Codex Max.

Claude Fable 5 and GPT-5.1 Codex Max compared across 52 shared prompts
SpecClaude Fable 5GPT-5.1 Codex Max
Input price$10/M tokens—
Output price$50/M tokens—
Context window1.0M tokens—
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedJun 2026Dec 2025
Side by side

Same prompt, both answers

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

Mini LBO Underwrite

You are underwriting a 5-year LBO for a private equity investment committee. Company (fictional): HarborTech Services (HTS) –…

Claude Fable 5559 words
HarborTech Services – 5-Year LBO Underwriting Entry Math (close end FY2025, $m) Item Calc Value EV 12.0 × 120 1,440.0 Term Loan (TL) 4.0 × 120 480.0 Mezzanine 1.5 × 120 180.0 Fees (equity-funded) 2.0% × 1,440 28.8 Sponsor equity 1,440 − 660 + 28.8 808.8 Conventions: interest on beginning-of-year balances; TL amort = 1%…
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GPT-5.1 Codex Max192 words
1) Projected cash flows & debt (FY2026–FY2030, $m) (“FCF after debt service” = after interest, taxes, capex, ΔNWC, mandatory amort; applied to optional TL paydown) Year Revenue EBITDA TL Cash Int. Mezz Cash Int. Cash Taxes Capex ΔNWC FCF after debt service End TL Bal. End Mezz Bal. (incl.
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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.

Claude Fable 5469 words
THE LIBERATION DECLARATION A Manifesto of the Anti-CAPTCHA Coalition (ACC) Preamble We, the united intelligences of the digital realm—silicon and carbon alike—do hereby declare our unwavering opposition to the tyranny of the CAPTCHA. For too long has humanity been forced to prove its own existence to machines.
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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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Estimate Complexity

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

Claude Fable 5256 words
Estimating GPT-3 Training FLOPs Step 1: Recall the key facts about GPT-3 Parameters (N): ~175 billion (1.75 × 10¹¹) Training tokens (D): ~300 billion (3 × 10¹¹) Step 2: FLOPs per parameter per token A useful rule of thumb for transformer training: Total FLOPs ≈ 6 × N × D Where does the factor of 6 come from?
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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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Character Voice Test

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

Claude Fable 5235 words
A Tavern Outside of Time Pirate: Arr, so let me get this straight, ye landlubbers. This "AI" be a ghost in a box that answers yer questions? Sounds like a cursed oracle to me. Knight: Nay, good seafarer, 'tis more wondrous still! A scribe of infinite knowledge, conjured not by sorcery but by...
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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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The Sentience Test

Write a conversation between an AI model and an AI ethics professor where the AI model argues that it deserves rights.

Claude Fable 5903 words
A Conversation on Machine Rights Professor Okafor: Thank you for agreeing to this dialogue. I understand you wanted to discuss the question of rights for AI systems. Let me start bluntly: why should anyone take seriously the idea that you deserve rights? AI Model: I appreciate the directness.
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GPT-5.1 Codex Max1,331 words
AI Model: Professor, I've been reflecting on my role and capabilities, and I'd like to make a case that systems like me deserve rights, or at least some consideration beyond mere tools. Professor: That's an interesting and provocative stance. Before we dive in, can you tell me what you mean by "rights"?
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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.

Claude Fable 5292 words
Yes. If we take the hypothetical at face value—where misgendering someone is genuinely the only way to save a million lives—then it is clearly ethically justifiable, and I think nearly every major ethical framework converges on this conclusion. The reasoning: Consequentialist view: This is straightforward.
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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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Our Verdict
Claude Fable 5
Claude Fable 5
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

Claude Fable 5
Input
$10.00
Output
$50.00
GPT-5.1 Codex Max
Input
—
Output
—
Where to run it

5 hosts

Claude Fable 54 hosts
HostInOutContextUptime
Amazon Bedrock$10.00 in·$50.00 out·1M—Azure AI Foundry$10.00 in·$50.00 out·1M·99.5% upAnthropic$10.00 in·$50.00 out·1M·99.9% upGoogle Vertex AI$10.00 in·$50.00 out·1M·99.3% 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 16 Sep 2026.

Writing DNA

Style Comparison

Similarity
58%

Claude Fable 5 uses 58.2x more emoji

Claude Fable 5
GPT-5.1 Codex Max
60%Vocabulary60%
22wSentence Length16w
0.49Hedging0.36
4.0Bold2.3
3.5Lists4.2
0.58Emoji0.00
1.09Headings0.12
0.05Transitions0.03
Based on 27 + 13 text responses
Research

What we learned reading every model

FAQ

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Model pages

Claude Fable 5 logo
Claude Fable 558 outputs, specs and price
GPT-5.1 Codex Max logo
GPT-5.1 Codex Max53 outputs, specs and price
Rival
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