ResearchLLM Verifications Leaderboard

Data as of · 78 models, 80 questions · reviewed by Suhas Bhairav · methodology

Head to head · tested 27 Oct 2026

Claude Fable 5.1 vs Claude Opus 5.5: accuracy, speed and price

Similar accuracy; Claude Opus 5.5 is faster.

AnthropicClaude Fable 5.181.2% score · #5$0.016 per question70 tok/sAnthropicClaude Opus 5.585.0% score · #1$0.015 per question129 tok/s

Verdict

Built from the measurements below

  • Accuracy is too close to call: Claude Fable 5.1 scored 81.2% and Claude Opus 5.5 85.0% on the same 80 questions, a gap within what chance alone could produce.
  • They cost about the same per question ($0.016 vs $0.015).
  • Claude Opus 5.5 generates text 1.8× faster: 129 tokens per second against 70.
  • Claude Fable 5.1 starts answering sooner: 2.1 s to the first token, against 2.3 s for Claude Opus 5.5.

Which should you choose?

Choose Claude Fable 5.1 for a quicker first token and shorter outputs (about 238 tokens per question against 645). Choose Claude Opus 5.5 for the lower cost per correct answer ($0.017 against $0.02) and faster streaming.

Accuracy gap -3.7 points (z = -0.63). A winner is called only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.

Head to head

Same questions, same prompt, same API

MeasureClaude Fable 5.1Claude Opus 5.5Edge
Verification scoreHigher is better81.2%85.0%Too close to call
Cost per questionLower is better$0.016$0.015Similar
Output speedHigher is better70129Claude Opus 5.5
Time to first tokenLower is better2.1 s2.3 sClaude Fable 5.1
End-to-end response timeLower is better11.0 s7.6 sClaude Opus 5.5
Tokens per questionLower is better238645Claude Fable 5.1
Context windowHigher is better1M1MSimilar

Side by side

Bars are scaled to the larger of the two values. The winner on each measure is marked in bold.

Every measure

Claude Fable 5.1 first, Claude Opus 5.5 second

Verification scorehigher is better
Claude Fable 5.181.2%
Claude Opus 5.585.0%
Cost per questionlower is better
Claude Fable 5.1$0.016
Claude Opus 5.5$0.015
Output speedhigher is better
Claude Fable 5.170
Claude Opus 5.5129
Time to first tokenlower is better
Claude Fable 5.12.1 s
Claude Opus 5.52.3 s
End-to-end response timelower is better
Claude Fable 5.111.0 s
Claude Opus 5.57.6 s
Tokens per questionlower is better
Claude Fable 5.1238
Claude Opus 5.5645
Context windowhigher is better
Claude Fable 5.11M
Claude Opus 5.51M

Score vs. cost per question

Both models in color, every other model in grey

Most attractive quadrant0255075100$0.00001$0.0001$0.001$0.01$0.10Cost per question (USD, log) →Verification score (%) →Qwen3.8 2.4T A95BCommand AReka Flash 3Gemma 4 26B A4BGemma 4 31BQwen3.5 397B A17BHermes 4 405BMuse WonderGrok 4.7o3gpt-oss-20bMinistral 3 3B 2512Nova Micro 1.0Phi 4Granite 4.2 8BHy3GLM 5.3 FlashSolar Pro 4Trinity Large ThinkingMiniMax M3Mistral Large 4Claude Opus 5.5GPT-6.1 SolGemini 4 ArgonGPT-5.4GPT-6 Lunagpt-oss-120bLlama 4 Maverick

Specifications and pricing

From OpenRouter's catalogue, plus the leaderboard's test dates

SpecificationClaude Fable 5.1Claude Opus 5.5
CreatorAnthropicAnthropic
Released1 Sept 202622 Sept 2026
Weights——
ReasoningYesYes
Inputtext, image, filetext, image, file
Outputtexttext
Context window1M tokens1M tokens
Knowledge cutoff——
List price in / out per 1M$10 / $50$4 / $20
Blended price per 1M (3:1)$20.00$8.00
Cheapest hostAzure · $10 / $50Amazon Bedrock · $4 / $20
Hosts on OpenRouter45
Last tested27 Oct 202625 Oct 2026

Compare any two models →

Claude Fable 5.1 vs Claude Opus 5.5: frequently asked questions

Is Claude Fable 5.1 better than Claude Opus 5.5?
On accuracy they are statistically tied: Claude Fable 5.1 scored 81.2% and Claude Opus 5.5 85.0% on the same 80 questions from open datasets. Similar accuracy; Claude Opus 5.5 is faster.
Which is cheaper, Claude Fable 5.1 or Claude Opus 5.5?
They cost about the same per question as billed: $0.016 for Claude Fable 5.1 and $0.015 for Claude Opus 5.5.
Which is faster, Claude Fable 5.1 or Claude Opus 5.5?
Claude Opus 5.5 is faster at 129 output tokens per second, against 70. Time to first token: 2.1 s for Claude Fable 5.1, 2.3 s for Claude Opus 5.5.
Which has the larger context window, Claude Fable 5.1 or Claude Opus 5.5?
Both accept about the same amount of context: 1M and 1M tokens.