Noometry

Model comparison

Claude Fable 5.1 vs Mercury 2.5

Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 33.5 on the Noometry Index. Mercury 2.5 costs 296× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.

Last verified . 4 shared benchmarks.

Claude Fable 5.1 Anthropic

69.0

Rank #2 Confirmed

Mercury 2.5 Inception

33.5

Rank #242 Reported

Summary

  • They share 4 benchmarks with published results for both. Claude Fable 5.1 scores higher in 3 categories and Mercury 2.5 in 0 categories; 3 gaps are clear of the uncertainty.
  • The widest gap is in math, where Claude Fable 5.1 leads 89.6 to 23.3.
  • The biggest single-benchmark swing is ProofBench: 100% for Claude Fable 5.1 and 3% for Mercury 2.5.
  • Mercury 2.5 is cheaper at $0.04 / $0.15 per million input/output tokens, against $10 / $50 for Claude Fable 5.1.
  • Claude Fable 5.1 accepts more context: 1M tokens versus 260K.

Side by side

Claude Fable 5.1Mercury 2.5
ProviderAnthropicInception
Noometry Index69.033.5
Released2026-09-012026-09-08
WeightsProprietaryProprietary
Context window1M260K
Max output128K66K
Input $ / M tokens$10$0.04
Output $ / M tokens$50$0.15
Results tracked524

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Category by category

Coding Claude Fable 5.1 leads

Claude Fable 5.1: 74.7 (#1), Mercury 2.5: 39.5 (#156)

BenchmarkClaude Fable 5.1Mercury 2.5
SciCode63.1%38.5%
ALE-Bench2,143301.65
FrontierCode50.9%—
CursorBench51.8%—
LMArena WebDev1744—
FrontierSWE56.3%—
GSO88.2%—
WeirdML92.9%—
LMArena Coding1528—
MirrorCode73.3%—

Agentic & Tool Use Not comparable

Claude Fable 5.1: 50.7 (#5), Mercury 2.5: —

BenchmarkClaude Fable 5.1Mercury 2.5
APEX-Agents68.6%—
Remote Labor Index17.9%—
GDP.pdf29.6%—
Vending-Bench 25,422—

Reasoning Claude Fable 5.1 leads

Claude Fable 5.1: 76.7 (#7), Mercury 2.5: 22.4 (#193)

BenchmarkClaude Fable 5.1Mercury 2.5
CritPt31.1%0%
ARC-AGI-290%—
NYT Connections (extended)90%—
ARC-AGI-197.5%—
Chess Puzzles47%—
EBR-Bench57.1%—
LMArena Hard Prompts1526—
Mystery Game Puzzles58%—
DTBench97.6%—
LMCA65.5%—
Epoch Capabilities Index164.7—

Math Claude Fable 5.1 leads

Claude Fable 5.1: 89.6 (#4), Mercury 2.5: 23.3 (#272)

BenchmarkClaude Fable 5.1Mercury 2.5
ProofBench100%3%
FrontierMath (Tiers 1-3)90.2%—
FrontierMath Tier 487.8%—
OTIS Mock AIME 2024-2025100%—
LMArena Math1525—
FrontierMath Erdős0%—

Knowledge Not comparable

Claude Fable 5.1: 69.6 (#6), Mercury 2.5: —

BenchmarkClaude Fable 5.1Mercury 2.5
Humanity's Last Exam46.5%—
SimpleQA Verified70.8%—
LMArena Expert1535—

Multimodal Not comparable

Claude Fable 5.1: 53.9 (#4), Mercury 2.5: —

BenchmarkClaude Fable 5.1Mercury 2.5
LMArena Vision1318—
Blueprint-Bench 241.9%—
Furniture Assembly70%—
LMArena Document1513—

Multilingual Not comparable

Claude Fable 5.1: 59.1 (#3), Mercury 2.5: —

BenchmarkClaude Fable 5.1Mercury 2.5
LMArena Non-English1507—
LMArena Chinese1586—
LMArena French1525—
LMArena German1500—
LMArena Japanese1543—
LMArena Korean1534—
LMArena Russian1521—
LMArena Spanish1516—

Instruction Following Not comparable

Claude Fable 5.1: 79.2 (#6), Mercury 2.5: —

BenchmarkClaude Fable 5.1Mercury 2.5
LMArena Instruction Following1517—

Long Context Not comparable

Claude Fable 5.1: 46.7 (#20), Mercury 2.5: —

BenchmarkClaude Fable 5.1Mercury 2.5
LMArena Longer Query1522—

Writing & Preference Not comparable

Claude Fable 5.1: 79.2 (#2), Mercury 2.5: —

BenchmarkClaude Fable 5.1Mercury 2.5
LMArena Text1510—
LMArena Creative Writing1507—
EQ-Bench Creative Writing2162—
LMArena Multi-Turn1492—

Frequently asked questions

Is Claude Fable 5.1 better than Mercury 2.5?

Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 33.5 on the Noometry Index. Mercury 2.5 costs 296× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.

Which is cheaper, Claude Fable 5.1 or Mercury 2.5?

Mercury 2.5 is cheaper. It lists at $0.04 per million input tokens and $0.15 per million output tokens; Claude Fable 5.1 lists at $10 and $50.

Is Claude Fable 5.1 or Mercury 2.5 better for coding?

Claude Fable 5.1 scores higher on coding benchmarks: 74.7 versus 39.5 in the Noometry coding category.

Which has the bigger context window?

Claude Fable 5.1 does, with 1M tokens against 260K.

How many benchmarks do Claude Fable 5.1 and Mercury 2.5 share?

4 benchmarks have published results for both models. Claude Fable 5.1 has 52 scored results on Noometry and Mercury 2.5 has 4.

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