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Comparison · 2 models · Updated Oct 4, 2026

Claude Fable 5.1 vs Fugu Ultra

Claude Fable 5.1 comes out ahead, 36 to 33 on our weighted score, though Fugu Ultra is 44% cheaper per token.

  1. Our pick

    Anthropic

    Claude Fable 5.1

    Released Sep 1, 2026

    36/100
    • ECI164.8
    • Price$10.00 / $50.00
    • Context1M
    Full specs Remove Claude Fable 5.1

  2. Sakana AI

    Fugu Ultra

    Released Jun 15, 2026

    33/100
    • ECI—
    • Price$5.00 / $30.00
    • Context1M
    Full specs Remove Fugu Ultra

  3. Add a model

    Make it a three-way comparison.

01 — Verdict

Claude Fable 5.1 is our pick

Claude Fable 5.1 is the better all-round choice, scoring 36/100 against Fugu Ultra (33). It leads on inputs & features. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.

  • CapabilityNot enough dataNo independent benchmark covers every model here yet
  • Lowest priceFugu UltraFugu Ultra $11.25 · Claude Fable 5.1 $20.00 per 1M tokens (3:1 blend)
  • Longest contextAbout the sameClaude Fable 5.1 1,000,000 · Fugu Ultra 1,000,000 tokens
  • Widest inputsClaude Fable 5.1Claude Fable 5.1: Text, Images, PDFs · Fugu Ultra: Text, Images
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightClaude Fable 5.1Fugu Ultra
Price50%00
Inputs & features30%8070
Context window20%6060
Overall100%36/10033/100

Left out because at least one model lacks the data: capability. The remaining weights were rescaled.

02 — Side by side

Every spec in one table

Highlighted cells lead their row. Dashes mean the data is not published.

Claude Fable 5.1 vs Fugu Ultra specifications side by side
SpecificationClaude Fable 5.1AnthropicFugu UltraSakana AI
Capability
Capabilities Index (ECI)164.8—
ECI rank#4 of 148—
FrontierMath Tiers 1–3Research-level mathematics90.2%—
OTIS Mock AIME 2024–2025Competition mathematics100%—
SimpleQA VerifiedShort factual questions70.8%—
Price per million tokens
Input$10.00$5.00 (best)
Output$50.00$30.00 (best)
Cached input$0.25 (best)$0.50
Blended (3:1)$20.00$11.25 (best)
Long-context rateSame rateOver 272K: $10.00 / $45.00
Price sourceOfficial Anthropic APIOfficial Sakana AI API
Limits
Context window1,000,000 tokens1,000,000 tokens
Max output128,000 tokens—
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesNo
AudioNoNo
VideoNoNo
ReasoningYeslow · medium · high · xhigh · maxYeshigh · xhigh
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryProprietary
API model IDclaude-fable-5-1fugu-ultra
API providers29 (best)11
ReleasedSep 1, 2026Jun 15, 2026
Knowledge cutoffJun 2026—
03 — Cost

What would a month cost?

Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.

  • Claude Fable 5.1$200.00
  • Fugu Ultra$110.00
04 — Questions

Which should you choose?

Which is better: Claude Fable 5.1 or Fugu Ultra?

Claude Fable 5.1 is the better all-round choice, scoring 36/100 against Fugu Ultra (33). It leads on inputs & features. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.

Which is cheaper, Claude Fable 5.1 or Fugu Ultra?

Fugu Ultra is cheaper at $5.00 input / $30.00 output per million tokens (official Sakana AI API price). Claude Fable 5.1 costs $10.00 input / $50.00 output per million tokens (official Anthropic API price). At a typical mix of three input tokens to one output token, that is $11.25 per million tokens for Fugu Ultra versus $20.00 for Claude Fable 5.1 (1.8× as much).

Which scores higher on benchmarks?

There is no independent benchmark that covers both models yet. Claude Fable 5.1 has an ECI of 164.8 and Fugu Ultra has not been scored yet.

Which is better for coding?

There are no published SWE-bench Verified results for Claude Fable 5.1 and Fugu Ultra yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. Both support tool calling for agent workflows.

Which has the bigger context window?

Claude Fable 5.1 and Fugu Ultra share the same 1,000,000-token context window. Maximum output per response: Claude Fable 5.1 up to 128,000 tokens.

Which can read images, PDFs, audio or video?

Claude Fable 5.1 accepts text, images and PDFs; Fugu Ultra accepts text and images. Claude Fable 5.1 handles the widest range of inputs.

Are any of these open source?

No. Claude Fable 5.1 and Fugu Ultra are proprietary and only available through APIs and apps.

Which is newer?

Claude Fable 5.1 is the newest, released Sep 1, 2026. Fugu Ultra came out Jun 15, 2026. Knowledge cutoff: Claude Fable 5.1 Jun 2026.

How do you decide the winner?

Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.

05 — Keep comparing

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