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Head-to-head comparison

Claude Fable 5.1 vs Gemini 3.8 Flash

Claude Fable 5.1 (Anthropic) and Gemini 3.8 Flash (Google) 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 18 October 2026

As of 18 October 2026, Claude Fable 5.1 holds the stronger ModelCap Index position (#3 vs #5); and Gemini 3.8 Flash is 12.1× cheaper per output token ($4.13/1M vs $50.00/1M).

Which should you choose?

Choose Claude Fable 5.1 if…

  • you want the stronger overall ModelCap Index position — #3 against #5 (85.8 vs 83.5 points).
  • you want provider choice — 4 listed API providers against 2.
  • Arena text is your yardstick — 1502 against 1496.
  • Arena coding is your yardstick — 1537 against 1528.
  • LMArena Agent is your yardstick — 14.0% against 3.7%.
  • ARC-AGI-2 is your yardstick — 90.0% against 89.2%.
  • AA Intelligence Index is your yardstick — 53.4 against 40.9.
  • AA Terminal-Bench 2.1 is your yardstick — 91.4% against 87.6%.
  • AA Humanity's Last Exam is your yardstick — 59.1% against 47.8%.
  • Terminal-Bench 4.0 is your yardstick — 57.9% against 19.1%.

Choose Gemini 3.8 Flash if…

  • API cost matters — $4.13/1M output tokens against $50.00/1M, about 12.1× cheaper.
  • your workload is prompt-heavy — input tokens cost $0.825/1M against $10.00/1M.
  • you want the more recently listed model — Gemini 3.8 Flash was listed 2 September 2026, Claude Fable 5.1 1 September 2026.

Claude Fable 5.1 vs Gemini 3.8 Flash: specs, pricing and context

Specification comparison of Claude Fable 5.1 and Gemini 3.8 Flash
FieldClaude Fable 5.1AnthropicGemini 3.8 FlashGoogle
ModelCap Index position#3#5
Index score85.883.5
EvidenceMeasuredMeasured
Input price / 1M tokens$10.00$0.825
Output price / 1M tokens$50.00$4.13
Context window1M tokens1M tokens
Declared route output cap128K66K
API providers listed42
Weight accessNo linked weightsNo linked weights
Input modalitiesText, Image, FileText, Image, Video, File, Audio
First listed1 September 20262 September 2026
PublisherAnthropicGoogle

Evidence: 4 public benchmark observations across 4 boards · 5 public benchmark observations across 5 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: Claude Fable 5.1 vs Gemini 3.8 Flash

Public benchmark boards where Claude Fable 5.1 or Gemini 3.8 Flash has a published result
BoardClaude Fable 5.1Gemini 3.8 FlashLeads
Arena textArena (LMArena)15021496–1508Max14961492–1501HighClaude Fable 5.1
Arena codingArena (LMArena)15371526–1549Max15281521–1535HighClaude Fable 5.1
LMArena AgentLMArena14.0%12.0%–16.0%Max3.7%2.6%–4.8%HighClaude Fable 5.1
ARC-AGI-2ARC Prize Foundation90.0%Max89.2%HighClaude Fable 5.1
ARC-AGI-3ARC Prize Foundation—10.4%HighOnly one result
AA Intelligence IndexArtificial Analysis53.4Reasoning40.9HighClaude Fable 5.1
AA Terminal-Bench 2.1Artificial Analysis91.4%Reasoning87.6%HighClaude Fable 5.1
AA Humanity's Last ExamArtificial Analysis59.1%Reasoning47.8%HighClaude Fable 5.1
Terminal-Bench 4.0Terminal-Bench (Laude Institute)57.9%54.1%–61.6%Claude Code · Max19.1%15.7%–22.5%mini-SWE-agent · HighClaude Fable 5.1

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 Gemini 3.8 Flash: common questions

Is Claude Fable 5.1 better than Gemini 3.8 Flash?

Claude Fable 5.1 ranks higher on the ModelCap Index as of 18 October 2026: #3 against #5. 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. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.

Is Claude Fable 5.1 cheaper than Gemini 3.8 Flash?

Gemini 3.8 Flash is cheaper on output tokens: $4.13/1M against $50.00/1M. Input tokens are $10.00/1M for Claude Fable 5.1 and $0.825/1M for Gemini 3.8 Flash. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens. For 1,000 requests with 2,000 input and 500 output tokens each (2M input + 0.5M output), the listed-rate estimate is $45.00 for Claude Fable 5.1 versus $3.71 for Gemini 3.8 Flash. Gemini 3.8 Flash costs 91.8% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.

Which has the bigger context window, Claude Fable 5.1 or Gemini 3.8 Flash?

Both publish a 1M-token context window. OpenRouter catalogue or provider-endpoint declaration. Limits can vary by provider and prompt length; a model-wide maximum has not been independently verified.

Which is better for coding, Claude Fable 5.1 or Gemini 3.8 Flash?

Arena coding: Claude Fable 5.1 1537, Gemini 3.8 Flash 1528 — Claude Fable 5.1 leads. AA Terminal-Bench 2.1: Claude Fable 5.1 91.4%, Gemini 3.8 Flash 87.6% — Claude Fable 5.1 leads. Terminal-Bench 4.0: Claude Fable 5.1 57.9%, Gemini 3.8 Flash 19.1% — Claude Fable 5.1 leads.

Are Claude Fable 5.1 and Gemini 3.8 Flash open-weight models?

Claude Fable 5.1: No linked weights. Gemini 3.8 Flash: No linked weights. Open weights mean the checkpoint can be downloaded and self-hosted under its licence. A missing weight link does not identify every API or chat product that offers a model.

Where can I run Claude Fable 5.1 and Gemini 3.8 Flash?

ModelCap currently lists 4 API providers for Claude Fable 5.1 and 2 for Gemini 3.8 Flash, 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 Gemini 3.8 Flash comparison?

Every figure and ModelCap Index position comes from the same published snapshot dated 18 October 2026. Publication and page updates happen separately; use the snapshot date shown on the page.

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