Claude Fable 5.1 vs mercury-2.5-preview
Wins 5 of 5 areas
Coding · Agents · Reasoning · Facts · Long documents
Wins 0 of 5 areas
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Claude Fable 5.1 is the stronger all-rounder.mercury-2.5-preview 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
- FactsGetting facts right instead of making them up20Claude 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
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.
mercury-2.5-preview costs 98% 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
- Very hard expert questions across many subjectsHumanity's Last Exam+47.3points ahead
- Answers hard knowledge questions correctlyAA-Omniscience · Accuracy+44.5points ahead
- Code for real scientific research problemsSciCode+24.6points ahead
Where mercury-2.5-preview pulls ahead
No clear win on a test scored out of 100.
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
- GDPValClaude Fable 5.1 by 62.862.80+62.8
- Terminal-Bench 4.0Claude Fable 5.1 by 52520+52
ReasoningClaude Fable 5.1
- Humanity's Last ExamClaude Fable 5.1 by 47.359.111.8+47.3
- CritPtClaude Fable 5.1 by 29.729.70+29.7
FactsClaude Fable 5.1
- AA-Omniscience · AccuracyClaude Fable 5.1 by 44.567.222.6+44.5
- AA-Omniscience · Non-hallucinationClaude Fable 5.1 by 7.727.419.7+7.7
Long documentsClaude Fable 5.1
- AA-LCRClaude Fable 5.1 by 13.685.371.7+13.6
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 8343.5-39.5+83
- AA IntelligenceClaude Fable 5.1 by 41.153.412.3+41.1
Questions people ask
Which is better, Claude Fable 5.1 or mercury-2.5-preview?
Claude Fable 5.1 wins all five areas where both have results: coding, agents, reasoning, facts and long documents. mercury-2.5-preview wins none, but costs 98% less.
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; mercury-2.5-preview costs $0.25 and $0.75. That makes mercury-2.5-preview about 98% 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.