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  5. Claude Fable 5vsClaude Opus 5.5
Updated Sep 2026

Claude Fable 5vsClaude Opus 5.5

Claude Opus 5.5 is cheaper than Claude Fable 5 at $4/M vs $10/M input tokens.

Claude Fable 5 and Claude Opus 5.5 compared across 19 shared prompts
SpecClaude Fable 5Claude Opus 5.5
Input price$10/M tokens$4/M tokens
Output price$50/M tokens$20/M tokens
Context window1.0M tokens1.0M tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedJun 2026Sep 2026
Side by side

Same prompt, both answers

Opening lines from 6 of the 19 prompts both answered. Formatting stripped, words untouched.

Michelin Star Recipe Design

Design an innovative recipe for a multi-component dish worthy of a Michelin 3-star restaurant. The recipe should feature an unusual…

Claude Fable 51,269 words
"WHERE THE FOREST DROWNS" Koji-Aged Scallop · Smoked Bone Marrow Custard · Fermented Gooseberry · Douglas Fir The Conceptual Narrative This dish is built on a memory of the Pacific Northwest coastline at low tide — where conifer forests grow so close to the sea that pine needles fall directly into tide pools.
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Claude Opus 5.52,253 words
"Hive & Tide" Langoustine, Beeswax, White Chocolate & Oscietra Caviar, Hay-Baked Celeriac, Fermented Green Strawberry, Sea Buckthorn I. The Concept Most coastal menus celebrate the meeting of sea and land. This dish is about a stranger, quieter meeting: the meadow and the seabed, the bee and the langoustine.
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Debug This Architecture

Here's the architecture for a real-time collaborative document editor (like Google Docs): **System Overview:** - Frontend: React SPA with…

Claude Fable 51,932 words
Architecture Review: Critical Issues & Solutions 🔴 Critical: Data Loss & Correctness Issues Client clock timestamps for conflict resolution Problem: Client clocks are unreliable—skew, drift, timezone bugs, and deliberate manipulation. A user with a clock 5 minutes fast will always win conflicts.
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Claude Opus 5.52,280 words
Architecture Review: Real-Time Collaborative Editor The most serious problems cluster in three areas: the sync model (client-clock LWW), cross-server propagation (per-server WebSockets with DB polling), and the CDN/auth layer, which can leak data between users. Issues are grouped by area below.
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Historical Counterfactual Analysis

If the transistor had been invented in 1920 instead of 1947, trace the likely technological, economic, and geopolitical implications through…

Claude Fable 51,363 words
The Transistor in 1920: An Alternate Timeline First, the Critical Caveat: A Slow Start A 1920 transistor would have been discovered *empirically*—likely an accidental extension of the crystal detector ("cat's whisker") work already underway. This matters enormously.
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Claude Opus 5.53,435 words
The Transistor in 1920: A Counterfactual Through 1980 First, a Reality Check on the Premise A transistor "invented" in 1920 would not have changed the world in 1920. The actual 1947 transistor rested on three foundations that did not exist yet: Quantum theory of solids.
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Advanced Longevity Plan (Biohacker)

Develop a comprehensive, cutting-edge 3-month longevity plan for a biohacker aiming to optimize longevity, physical and cognitive…

Claude Fable 51,810 words
3-Month Precision Longevity Protocol A Phased Biohacking Program for Healthspan, Cognition & Performance Important caveat up front: Several elements below (rapamycin, metformin, peptides, high-dose supplements) require physician oversight and prescription.
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Claude Opus 5.53,099 words
The 90-Day Longevity & Performance Protocol A structured, measurable plan for the experienced biohacker How to Use This Plan Philosophy: Measure → Intervene → Re-measure. Every intervention has a hypothesis, a metric, and a decision rule.
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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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Claude Opus 5.5900 words
HarborTech Services: 5-Year LBO Underwriting Conventions: $m. Interest is charged on beginning-of-year balances, which avoids circularity. Term Loan (TL) amortization is 1% of the original $480m, or $4.8m per year. Mezz PIK accrues to principal. All FCF after mandatory debt service sweeps to the TL.
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Explain Like I'm a Specific Expert

Explain how a large language model (like GPT or Claude) learns and generates text to each of these three audiences: 1. **An experienced…

Claude Fable 51,150 words
The Skeptical Software Engineer Think of an LLM as the world's most aggressive lossy compression problem. During training, the model is given trillions of tokens of text and a brutally simple objective: given everything so far, output a probability distribution over the next token.
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Claude Opus 5.51,442 words
How Large Language Models Work: Three Explanations For the Experienced Software Engineer Think of an LLM as a single, very large pure function: f(tokens[0..n]) → probability distribution over tokens[n+1]. Text is chunked into tokens (roughly word fragments, from a vocabulary of about 100k).
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Our Verdict
Claude Fable 5
Claude Fable 5
Claude Opus 5.5
Claude Opus 5.5

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
Claude Opus 5.5
Input
$4.00
2.5× cheaper
Output
$20.00
2.5× cheaper

Claude Opus 5.5 is cheaper on both: 2.5× input, 2.5× output.

Where to run it

8 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·99.7% upAnthropic$10.00 in·$50.00 out·1M·100% upGoogle Vertex AI$10.00 in·$50.00 out·1M·99.7% up
Claude Opus 5.54 hosts
HostInOutContextUptime
Amazon Bedrock$4.00 in·$20.00 out·1M·99.8% upAzure AI Foundry$4.00 in·$20.00 out·1M·100% upAnthropic$4.00 in·$20.00 out·1M·100% upGoogle Vertex AI$4.00 in·$20.00 out·1M·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 25 Sep 2026.

Research

What we learned reading every model

FAQ

Common questions

Both are developed by Anthropic but target different use cases. Claude Fable 5 has a 1.0M token context window vs Claude Opus 5.5's 1.0M. You can compare their actual outputs across 19 challenges on Rival to see how they differ in practice.

It depends on your use case. Claude Fable 5 and Claude Opus 5.5 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 19 challenges so you can judge which fits your needs best.

Claude Fable 5 costs $10/M input tokens and Claude Opus 5.5 costs $4/M input tokens. Claude Opus 5.5 is $6.00/M cheaper per input. Check their side-by-side outputs on Rival to see if the price difference is justified by quality.

This page shows a side-by-side comparison of Claude Fable 5 and Claude Opus 5.5 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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