ZMIME
Comparison · 2 models · Updated Oct 4, 2026

GPT-5.5 vs Claude Fable 5.1

Claude Fable 5.1 comes out ahead, 66 to 63 on our weighted score, though GPT-5.5 is 44% cheaper per token.

  1. OpenAI

    GPT-5.5

    Released Apr 23, 2026

    63/100
    • ECI159.2
    • Price$5.00 / $30.00
    • Context1.05M
    Full specs Remove GPT-5.5
  2. Our pick

    Anthropic

    Claude Fable 5.1

    Released Sep 1, 2026

    66/100
    • ECI164.8
    • Price$10.00 / $50.00
    • Context1M
    Full specs Remove Claude Fable 5.1

  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 66/100 against GPT-5.5 (63). It leads on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityClaude Fable 5.1Capabilities Index (ECI): Claude Fable 5.1 164.8 · GPT-5.5 159.2
  • Lowest priceGPT-5.5GPT-5.5 $11.25 · Claude Fable 5.1 $20.00 per 1M tokens (3:1 blend)
  • Longest contextGPT-5.5GPT-5.5 1,050,000 · Claude Fable 5.1 1,000,000 tokens
  • Widest inputsSame inputsGPT-5.5: Text, Images, PDFs · Claude Fable 5.1: Text, Images, PDFs
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightGPT-5.5Claude Fable 5.1
CapabilityCapabilities Index (ECI)50%9097
Price25%00
Inputs & features15%8080
Context window10%6160
Overall100%63/10066/100
02 — Side by side

Every spec in one table

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

GPT-5.5 vs Claude Fable 5.1 specifications side by side
SpecificationGPT-5.5OpenAIClaude Fable 5.1Anthropic
Capability
Capabilities Index (ECI)159.2164.8 (best)
ECI rank#10 of 148#4 of 148 (best)
GPQA DiamondGraduate-level science questions94.0%—
FrontierMath Tiers 1–3Research-level mathematics85.3%90.2% (best)
OTIS Mock AIME 2024–2025Competition mathematics100%100%
SWE-bench VerifiedFixing real GitHub issues80.6%—
SimpleQA VerifiedShort factual questions63.0%70.8% (best)
Price per million tokens
Input$5.00 (best)$10.00
Output$30.00 (best)$50.00
Cached input$0.50$0.25 (best)
Blended (3:1)$11.25 (best)$20.00
Long-context rateOver 272K: $10.00 / $45.00Same rate
Price sourceOfficial OpenAI APIOfficial Anthropic API
Limits
Context window1,050,000 tokens (best)1,000,000 tokens
Max output128,000 tokens128,000 tokens
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesYes
AudioNoNo
VideoNoNo
ReasoningYeslow · medium · high · xhighYeslow · medium · high · xhigh · max
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryProprietary
API model IDgpt-5.5claude-fable-5-1
API providers42 (best)29
ReleasedApr 23, 2026Sep 1, 2026
Knowledge cutoffDec 1, 2025Jun 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.

  • GPT-5.5$110.00
  • Claude Fable 5.1$200.00
04 — Questions

Which should you choose?

Which is better: GPT-5.5 or Claude Fable 5.1?

Claude Fable 5.1 is the better all-round choice, scoring 66/100 against GPT-5.5 (63). It leads on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

Which is cheaper, GPT-5.5 or Claude Fable 5.1?

GPT-5.5 is cheaper at $5.00 input / $30.00 output per million tokens (official OpenAI 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 GPT-5.5 versus $20.00 for Claude Fable 5.1 (1.8× as much).

Which scores higher on benchmarks?

Claude Fable 5.1 scores higher on the Capabilities Index (ECI): Claude Fable 5.1 164.8 (#4 of 148) and GPT-5.5 159.2 (#10 of 148). The confidence ranges of the top two overlap (161.8–169.1 vs 156.9–162.4), so treat the gap as small. On individual benchmarks: FrontierMath Tiers 1–3 — Claude Fable 5.1 90.2%, GPT-5.5 85.3%; OTIS Mock AIME 2024–2025 — GPT-5.5 100%, Claude Fable 5.1 100%; SimpleQA Verified — Claude Fable 5.1 70.8%, GPT-5.5 63.0%.

Which is better for coding?

There are no published SWE-bench Verified results for Claude Fable 5.1 yet, so there is no like-for-like coding score. On overall capability, Claude Fable 5.1 leads, which tends to carry over to coding, but test on your own codebase. Both support tool calling for agent workflows.

Which has the bigger context window?

GPT-5.5 has the largest context window at 1,050,000 tokens, against 1,000,000 for Claude Fable 5.1. Maximum output per response: GPT-5.5 up to 128,000, Claude Fable 5.1 up to 128,000 tokens.

Which can read images, PDFs, audio or video?

GPT-5.5 accepts text, images and PDFs; Claude Fable 5.1 accepts text, images and PDFs. They handle the same number of input types.

Are any of these open source?

No. GPT-5.5 and Claude Fable 5.1 are proprietary and only available through APIs and apps.

Which is newer?

Claude Fable 5.1 is the newest, released Sep 1, 2026. GPT-5.5 came out Apr 23, 2026. Knowledge cutoff: GPT-5.5 Dec 1, 2025, 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

Related comparisons