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Head-to-head comparison

Claude Fable 5.1 vs Claude Opus 5.5

Claude Fable 5.1 (Anthropic) and Claude Opus 5.5 (Anthropic) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.

Snapshot as of 6 November 2026

As of 6 November 2026, Claude Opus 5.5 holds the stronger ModelCap Index position (#1 vs #3); and Claude Opus 5.5 is 2.5× cheaper per output token ($20.00/1M vs $50.00/1M).

Which should you choose?

Choose Claude Fable 5.1 if…

  • ModelCap publishes no field on which Claude Fable 5.1 leads Claude Opus 5.5 for this pair.

Choose Claude Opus 5.5 if…

  • you want the stronger overall ModelCap Index position — #1 against #3 (87.7 vs 86.0 points).
  • API cost matters — $20.00/1M output tokens against $50.00/1M, about 2.5× cheaper.
  • your workload is prompt-heavy — input tokens cost $4.00/1M against $10.00/1M.
  • you want provider choice — 5 listed API providers against 4.
  • Arena text is your yardstick — 1509 against 1504.
  • Arena coding is your yardstick — 1551 against 1537.
  • LMArena Agent is your yardstick — 20.1% against 13.9%.
  • ARC-AGI-2 is your yardstick — 93.3% against 90.0%.
  • AA Intelligence Index is your yardstick — 59.1 against 49.2.
  • Terminal-Bench 4.0 is your yardstick — 64.9% against 57.9%.
  • you want the more recently listed model — Claude Opus 5.5 was listed 22 September 2026, Claude Fable 5.1 1 September 2026.

Claude Fable 5.1 vs Claude Opus 5.5: specs, pricing and context

Specification comparison of Claude Fable 5.1 and Claude Opus 5.5
FieldClaude Fable 5.1AnthropicClaude Opus 5.5Anthropic
ModelCap Index position#3#1
Index score86.087.7
EvidenceMeasuredMeasured
Input price / 1M tokens$10.00$4.00
Output price / 1M tokens$50.00$20.00
Context window1M tokens1M tokens
Declared route output cap128K128K
API providers listed45
Weight accessNo linked weightsNo linked weights
Input modalitiesText, Image, FileText, Image, File
First listed1 September 202622 September 2026
PublisherAnthropicAnthropic

Evidence: 4 public benchmark observations across 4 boards · 4 public benchmark observations across 4 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: Claude Fable 5.1 vs Claude Opus 5.5

Public benchmark boards where Claude Fable 5.1 or Claude Opus 5.5 has a published result
BoardClaude Fable 5.1Claude Opus 5.5Leads
Arena textArena (LMArena)15041499–1510Max15091502–1515HighClaude Opus 5.5
Arena codingArena (LMArena)15371526–1547Max15511538–1563HighClaude Opus 5.5
LMArena AgentLMArena13.9%12.0%–15.7%Max20.1%18.1%–22.2%MaxClaude Opus 5.5
ARC-AGI-2ARC Prize Foundation90.0%Max93.3%HighClaude Opus 5.5
AA Intelligence IndexArtificial Analysis49.2Max59.1MaxClaude Opus 5.5
Terminal-Bench 4.0Terminal-Bench (Laude Institute)57.9%54.1%–61.6%Claude Code · Max64.9%61.7%–68.0%Claude Code · MaxClaude Opus 5.5

Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.

Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.

Claude Fable 5.1 vs Claude Opus 5.5: common questions

Is Claude Fable 5.1 better than Claude Opus 5.5?

Claude Opus 5.5 ranks higher on the ModelCap Index as of 6 November 2026: #1 against #3. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.

Is Claude Fable 5.1 cheaper than Claude Opus 5.5?

Claude Opus 5.5 is cheaper on output tokens: $20.00/1M against $50.00/1M. Input tokens are $10.00/1M for Claude Fable 5.1 and $4.00/1M for Claude Opus 5.5. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens. For 1,000 requests with 2,000 input and 500 output tokens each (2M input + 0.5M output), the listed-rate estimate is $45.00 for Claude Fable 5.1 versus $18.00 for Claude Opus 5.5. Claude Opus 5.5 costs 60.0% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.

Which has the bigger context window, Claude Fable 5.1 or Claude Opus 5.5?

Both publish a 1M-token context window. OpenRouter catalogue or provider-endpoint declaration. Limits can vary by provider and prompt length; a model-wide maximum has not been independently verified.

Which is better for coding, Claude Fable 5.1 or Claude Opus 5.5?

Arena coding: Claude Fable 5.1 1537, Claude Opus 5.5 1551 — Claude Opus 5.5 leads. Terminal-Bench 4.0: Claude Fable 5.1 57.9%, Claude Opus 5.5 64.9% — Claude Opus 5.5 leads.

Are Claude Fable 5.1 and Claude Opus 5.5 open-weight models?

Claude Fable 5.1: No linked weights. Claude Opus 5.5: No linked weights. Open weights mean the checkpoint can be downloaded and self-hosted under its licence. A missing weight link does not identify every API or chat product that offers a model.

Where can I run Claude Fable 5.1 and Claude Opus 5.5?

ModelCap currently lists 4 API providers for Claude Fable 5.1 and 5 for Claude Opus 5.5, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.

How current is this Claude Fable 5.1 vs Claude Opus 5.5 comparison?

Every figure and ModelCap Index position comes from the same published snapshot dated 6 November 2026. Publication and page updates happen separately; use the snapshot date shown on the page.

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