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Head-to-head comparison

Claude Fable 5.1 vs Claude Sonnet 5

Claude Fable 5.1 (Anthropic) and Claude Sonnet 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 3 September 2026

As of 3 September 2026, Claude Fable 5.1 holds the stronger ModelCap Index position (#2 vs #15); and Claude Sonnet 5 is 5× cheaper per output token ($10.00/1M vs $50.00/1M).

Which should you choose?

Choose Claude Fable 5.1 if…

  • you want the stronger overall ModelCap Index position — #2 against #15 (84.1 vs 74.2 points).
  • AA Intelligence Index is your yardstick — 65.7 against 55.3.
  • AA Terminal-Bench 2.1 is your yardstick — 91.4% against 80.5%.
  • AA Humanity's Last Exam is your yardstick — 59.1% against 41.3%.
  • you want the more recently listed model — Claude Fable 5.1 was listed 1 September 2026, Claude Sonnet 5 30 June 2026.

Choose Claude Sonnet 5 if…

  • API cost matters — $10.00/1M output tokens against $50.00/1M, about 5× cheaper.
  • your workload is prompt-heavy — input tokens cost $2.00/1M against $10.00/1M.
  • you want provider choice — 5 listed API providers against 4.

Claude Fable 5.1 vs Claude Sonnet 5: specs, pricing and context

Specification comparison of Claude Fable 5.1 and Claude Sonnet 5
FieldClaude Fable 5.1AnthropicClaude Sonnet 5Anthropic
ModelCap Index position#2#15
Index score84.174.2
EvidenceMeasuredMeasured
Input price / 1M tokens$10.00$2.00
Output price / 1M tokens$50.00$10.00
Context window1M tokens1M tokens
Max output tokens128K128K
API providers listed45
Weight accessAPI onlyAPI only
Input modalitiesText, Image, FileText, Image, File
First listed1 September 202630 June 2026
PublisherAnthropicAnthropic

Evidence: 2 public benchmark observations across 2 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 Sonnet 5

Public benchmark boards where Claude Fable 5.1 or Claude Sonnet 5 has a published result
BoardClaude Fable 5.1Claude Sonnet 5Leads
Arena codingArena (LMArena)—15211513–1528HighOnly one result
LMArena AgentLMArena—7.5%5.3%–9.7%HighOnly one result
ARC-AGI-2ARC Prize Foundation90.0%Max—Only one result
AA Intelligence IndexArtificial Analysis65.7intelligence-index55.3intelligence-indexClaude Fable 5.1
AA Terminal-Bench 2.1Artificial Analysis91.4%terminal-bench-2.180.5%terminal-bench-2.1Claude Fable 5.1
AA Humanity's Last ExamArtificial Analysis59.1%humanitys-last-exam41.3%humanitys-last-examClaude Fable 5.1
Terminal-Bench 4.0Terminal-Bench (Laude Institute)—12.4%9.4%–15.5%Claude Code · MaxOnly one result

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 Sonnet 5: common questions

Is Claude Fable 5.1 better than Claude Sonnet 5?

Claude Fable 5.1 ranks higher on the ModelCap Index as of 3 September 2026: #2 against #15. 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.

Is Claude Fable 5.1 cheaper than Claude Sonnet 5?

Claude Sonnet 5 is cheaper on output tokens: $10.00/1M against $50.00/1M. Input tokens are $10.00/1M for Claude Fable 5.1 and $2.00/1M for Claude Sonnet 5. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens.

Which has the bigger context window, Claude Fable 5.1 or Claude Sonnet 5?

Both publish a 1M-token context window.

Which is better for coding, Claude Fable 5.1 or Claude Sonnet 5?

AA Terminal-Bench 2.1: Claude Fable 5.1 91.4%, Claude Sonnet 5 80.5% — Claude Fable 5.1 leads.

Are Claude Fable 5.1 and Claude Sonnet 5 open-weight models?

Claude Fable 5.1: API only. Claude Sonnet 5: API only. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.

Where can I run Claude Fable 5.1 and Claude Sonnet 5?

ModelCap currently lists 4 API providers for Claude Fable 5.1 and 5 for Claude Sonnet 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 Sonnet 5 comparison?

Every figure comes from the sealed ModelCap dataset published 3 September 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.

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