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Model comparison

Claude Fable 5.1 vs Gemini 3.1 Pro

Anthropic against Google, 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

Google

Gemini 3.1 Pro

Frontier

AI model capability comparison
SpecificationClaude Fable 5.1Gemini 3.1 Pro
ProviderAnthropicGoogle
TierFrontierFrontier
Context window1MWinner: 1.05M
Max outputWinner: 128K66K
Input / 1M tokens$10Winner: $2
Output / 1M tokens$50Winner: $12
WeightsClosedClosed
ParametersNot verifiedUnverifiedNot verifiedUnverified
Reasoning levelslow, medium, high, xhigh, maxlow, medium, high
Modalitiestext, imagetext, image, video, audio, pdf
API model idclaude-fable-5-1gemini-3.1-pro-preview
ReleasedSeptember 1, 2026February 19, 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, Gemini 3.1 Pro: 2026-02 (comparability not verified)6544.4
Terminal-Bench 2.1 · source date Claude Fable 5.1: 2026-09-26, Gemini 3.1 Pro: 2026-07 (comparability not verified)91.473.8
DeepSWE 1.1 · source date Claude Fable 5.1: 2026-09-0367.4Not verifiedUnverified
SWE-bench Verified · source date Gemini 3.1 Pro: 2026-02Not verifiedUnverified80.6
GPQA Diamond · source date Gemini 3.1 Pro: 2026-02Not verifiedUnverified94.3

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.

Gemini 3.1 Pro: The current Gemini developer guide lists $2/$12 per MTok below 200K input and $4/$18 above 200K, including thinking output. It leaves the exact 200K boundary unspecified; confirm that boundary and other processing/cache tiers before budgeting. The exact API ID remains gemini-3.1-pro-preview. Restricted Gemini 4 Argon is a separate preview and does not make this endpoint stable.

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

Gemini 3.1 Pro

Gemini 3.1 Pro Preview is Google's multimodal Pro endpoint with a 1,048,576-token input limit and 65,536-token output limit.

Best for

  • Very long documents
  • Multimodal reasoning
  • Frontier knowledge work

Watch out

This API endpoint remains Preview. A separate customtools endpoint is optimized for bash/custom-tool workflows and can behave differently on other tasks. Keep endpoint, thinking level and benchmark version matched; restricted Gemini 4 Argon access is a separate lifecycle.

When the cheaper one wins

Gemini 3.1 Pro is cheaper on output at $12 per million tokens against $50 for Claude Fable 5.1 — about 4.2×. 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.

Run the model picker

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 · Gemini 3.1 Pro

Common questions

Claude Fable 5.1 vs Gemini 3.1 Pro

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

Is Claude Fable 5.1 or Gemini 3.1 Pro cheaper for input?
Gemini 3.1 Pro is cheaper at $2 per million input tokens, against $10 for Claude Fable 5.1 — roughly 5.0× 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. Gemini 3.1 Pro: The current Gemini developer guide lists $2/$12 per MTok below 200K input and $4/$18 above 200K, including thinking output. It leaves the exact 200K boundary unspecified; confirm that boundary and other processing/cache tiers before budgeting. The exact API ID remains gemini-3.1-pro-preview. Restricted Gemini 4 Argon is a separate preview and does not make this endpoint stable.
Is Claude Fable 5.1 or Gemini 3.1 Pro cheaper for output?
Gemini 3.1 Pro is cheaper at $12 per million output tokens, against $50 for Claude Fable 5.1 — roughly 4.2× 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. Gemini 3.1 Pro: The current Gemini developer guide lists $2/$12 per MTok below 200K input and $4/$18 above 200K, including thinking output. It leaves the exact 200K boundary unspecified; confirm that boundary and other processing/cache tiers before budgeting. The exact API ID remains gemini-3.1-pro-preview. Restricted Gemini 4 Argon is a separate preview and does not make this endpoint stable.
Which has the larger context window, Claude Fable 5.1 or Gemini 3.1 Pro?
Gemini 3.1 Pro 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 Gemini 3.1 Pro support the same reasoning levels?
Claude Fable 5.1 exposes low, medium, high, xhigh, max, while Gemini 3.1 Pro exposes low, medium, high.
Should I use Claude Fable 5.1 or Gemini 3.1 Pro?
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; Gemini 3.1 Pro is a candidate for very long documents. 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: Gemini 3.1 Pro costs $2 per 1M tokens versus $10 for Claude Fable 5.1 — a 5x difference at the headline tier.
  • Context: Gemini 3.1 Pro takes 1.05M against 1M for Claude Fable 5.1 — only decisive if your prompts approach the smaller window.
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