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Model comparison

Claude Fable 5.1 vs GPT-5.5

Anthropic against OpenAI, compared on context, price, and attributed benchmark results.

Recorded profile verification October 1, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Fable 5.1

Frontier

vs

OpenAI

GPT-5.5

Frontier

AI model capability comparison
SpecificationClaude Fable 5.1GPT-5.5
ProviderAnthropicOpenAI
TierFrontierFrontier
Context window1MWinner: 1.05M
Max output128K128K
Input / 1M tokens$10Winner: $5
Output / 1M tokens$50Winner: $30
WeightsClosedClosed
ParametersNot verifiedUnverifiedNot verifiedUnverified
Reasoning levelslow, medium, high, xhigh, maxnone, low, medium, high, xhigh
Modalitiestext, imagetext, image
API model idclaude-fable-5-1gpt-5.5
ReleasedSeptember 1, 2026April 23, 2026
Artificial Analysis Intelligence Index [max] · source date Claude Fable 5.1: 2026-10-0153Not verifiedUnverified
Humanity's Last Exam · source date Claude Fable 5.1: 2026-09-01, GPT-5.5: 2026-04-23 (comparability not verified)6552.2
Terminal-Bench 2.1 · source date Claude Fable 5.1: 2026-09-26, GPT-5.5: 2026-07-27 (comparability not verified)91.483.4
DeepSWE 1.1 · source date Claude Fable 5.1: 2026-09-0367.4Not verifiedUnverified
GPQA Diamond · source date GPT-5.5: 2026-07-27Not verifiedUnverified93.5

Dates beside benchmark scores refer to the linked source’s publication or capture date unless that source explicitly states when it measured the result. A shared URL alone does not establish comparable runs; unverified setups are marked. Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

Pricing tiers

Claude Fable 5.1: Standard $10/$50 per MTok with no long-context surcharge. Cache reads $0.25, versus Fable 5's $1; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Adaptive thinking is always on, default effort high; knowledge cutoff Jun 2026. Retirement not sooner than September 1, 2027.

GPT-5.5: Standard $5/$30 per MTok; prompts above 272K bill 2x input and 1.5x output for the full session in Standard/Batch/Flex. Cached input $0.50; short-context Batch $2.50/$15. Regional/FedRAMP processing adds 10% where eligible.

FrontierRecord checked October 1, 2026

Claude Fable 5.1

Claude Fable 5.1 is Anthropic's model for the most demanding reasoning and long-horizon agentic work at $10/$50 — Anthropic now recommends Opus 5.5 as the default for most workloads.

Best for

  • Frontier agents
  • Hardest reasoning work
  • Fable 5 workloads at the same price

Watch out

Standard token rates are 2.5x Opus 5.5's. Forced tool use errors; thinking blocks are model/conversation-bound, so editing earlier turns or switching models can invalidate them. Display updates and per-message effort are beta. Match benchmark settings and evaluate pinned workloads before migrating.

FrontierRecord checked October 1, 2026

GPT-5.5

OpenAI’s April 2026 model for reasoning, coding and professional work, with a 1.05M-token context. Retained benchmark scores identify their source and configuration.

Best for

  • Reasoning
  • Agentic coding
  • Long-context work

Watch out

An older model, still listed in the API. GPT-5.5 retires from ChatGPT, Work and Codex on October 14, 2026; that notice does not affect the OpenAI API.

When the cheaper one wins

GPT-5.5 is cheaper on output at $30 per million tokens against $50 for Claude Fable 5.1 — about 1.7×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. This compares standard short-context token rates, not total cost per accepted task. Include input, cache, context tiers, schedules, retries and review in your pilot.

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Evidence confidence: Medium

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

  • Pricing verified on both sides — Input and output rates are verified for both models.
  • 4/5 core specs verified on both sides — Not published for at least one side: parameter count.
  • No directly aligned benchmark setup — No benchmark has matching cited sources, source dates, units, effort and recorded run details on both models.
  • Verified within the last 90 days — Older of the two catalog checks was 25 days ago.
  • Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

Related comparisons

Diving deeper on one model? Claude Fable 5.1 · GPT-5.5

Common questions

Claude Fable 5.1 vs GPT-5.5

Answered from the verified figures on this page rather than general guidance.

Is Claude Fable 5.1 or GPT-5.5 cheaper for input?
GPT-5.5 is cheaper at $5 per million input tokens, against $10 for Claude Fable 5.1 — roughly 2.0× the price. Estimate both input and output token volume for your workload. These are base rates; Claude Fable 5.1: Standard $10/$50 per MTok with no long-context surcharge. Cache reads $0.25, versus Fable 5's $1; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Adaptive thinking is always on, default effort high; knowledge cutoff Jun 2026. Retirement not sooner than September 1, 2027. GPT-5.5: Standard $5/$30 per MTok; prompts above 272K bill 2x input and 1.5x output for the full session in Standard/Batch/Flex. Cached input $0.50; short-context Batch $2.50/$15. Regional/FedRAMP processing adds 10% where eligible.
Is Claude Fable 5.1 or GPT-5.5 cheaper for output?
GPT-5.5 is cheaper at $30 per million output tokens, against $50 for Claude Fable 5.1 — roughly 1.7× the price. Estimate both input and output token volume for your workload. These are base rates; Claude Fable 5.1: Standard $10/$50 per MTok with no long-context surcharge. Cache reads $0.25, versus Fable 5's $1; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Adaptive thinking is always on, default effort high; knowledge cutoff Jun 2026. Retirement not sooner than September 1, 2027. GPT-5.5: Standard $5/$30 per MTok; prompts above 272K bill 2x input and 1.5x output for the full session in Standard/Batch/Flex. Cached input $0.50; short-context Batch $2.50/$15. Regional/FedRAMP processing adds 10% where eligible.
Which has the larger context window, Claude Fable 5.1 or GPT-5.5?
GPT-5.5 accepts 1.05M tokens against 1M for Claude Fable 5.1. This only matters if you routinely send very long documents or large codebases.
Do Claude Fable 5.1 and GPT-5.5 support the same reasoning levels?
Claude Fable 5.1 exposes low, medium, high, xhigh, max, while GPT-5.5 exposes none, low, medium, high, xhigh.
Should I use Claude Fable 5.1 or GPT-5.5?
Both are classified in our frontier tier; this editorial grouping does not imply equal capability. Claude Fable 5.1 is a candidate for frontier agents; GPT-5.5 is a candidate for reasoning. Compare accuracy, tool reliability, latency and cost on representative tasks.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

  • Input price: GPT-5.5 costs $5 per 1M tokens versus $10 for Claude Fable 5.1 — a 2x difference at the headline tier.
  • Context: GPT-5.5 takes 1.05M against 1M for Claude Fable 5.1 — only decisive if your prompts approach the smaller window.
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