Claude Fable 5.1 vs Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback)
Wins 4 of 5 areas
Coding · Agents · Reasoning · Long documents
Wins 0 of 5 areas
—
Claude Fable 5.1 is the stronger all-rounder.Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback) is cheaper.
Scores updated · 10 tests both models report · How we compare
Where each one wins
Tests won in each of the five areas where both have results. Each piece is one test, so a longer bar means more evidence; grey means the two scored within a point of each other.
- AgentsCarrying out multi-step tasks on its own20Claude Fable 5.12 of 2 tests
- ReasoningHard problems that need careful thinking20Claude Fable 5.12 of 2 tests
- CodingWriting and fixing software10Claude Fable 5.11 of 1 test
- Long documentsFinding answers in very long texts10Claude Fable 5.11 of 1 test
- FactsGetting facts right instead of making them up11Even1 each
Coding and long documents rest on a single test each.
What it costs
Prices per million tokens, roughly 750,000 words. The bars show the cost of a million tokens read plus a million written.
Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback) costs 80% less for the same work.
The biggest differences
The tests each model wins by the widest margin, up to three each. Scores are out of 100.
Where Claude Fable 5.1 pulls ahead
- Complex command-line tasks across many fieldsTerminal-Bench 4.0+31.3points ahead
- Real work tasks from 44 professionsGDPVal+28.9points ahead
- Very hard expert questions across many subjectsHumanity's Last Exam+22.9points ahead
Where Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback) pulls ahead
- Avoids making up answers it doesn't knowAA-Omniscience · Non-hallucination+22.4points ahead
Every test, side by side
All 10 tests both models report. The winning score is in its model's colour; marks a score checked independently.
AgentsClaude Fable 5.1
- Terminal-Bench 4.0Claude Fable 5.1 by 31.35220.7+31.3
- GDPValClaude Fable 5.1 by 28.962.833.9+28.9
ReasoningClaude Fable 5.1
- Humanity's Last ExamClaude Fable 5.1 by 22.959.136.2+22.9
- CritPtClaude Fable 5.1 by 18.329.711.4+18.3
FactsEven
- AA-Omniscience · Non-hallucinationClaude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback) by 22.427.449.8+22.4
- AA-Omniscience · AccuracyClaude Fable 5.1 by 20.967.246.3+20.9
Other results2 tests, not counted
Tests outside the eight areas. They are not counted above: several are summary scores built from other tests, or the same test under another name.
- AA-OmniscienceClaude Fable 5.1 by 24.143.519.4+24.1
- AA IntelligenceClaude Fable 5.1 by 17.553.435.9+17.5
Questions people ask
Which is better, Claude Fable 5.1 or Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback)?
Claude Fable 5.1 wins four of the five areas where both have results: coding, agents, reasoning and long documents. Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback) wins none, but costs 80% less. They are level on facts.
Which is better for coding?
Claude Fable 5.1. It wins the one coding test both models report.
Which is cheaper?
Claude Fable 5.1 costs $10.00 per million input tokens and $50.00 per million output tokens; Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback) costs $2.00 and $10.00. That makes Claude Sonnet 5.5 (Adaptive Reasoning, Low Effort, Default Fallback) about 80% cheaper for the same work.
How do you compare the two?
We use the 10 benchmark tests both models have published scores on. The verdict counts the 8 tests in the eight capability areas, and a gap under one point (ten on rating-style scales) counts as a tie. The other 2 are listed but not counted, because several are summary scores or repeat a test. Each score is the one shown on the model's own page.