Model comparison
Claude Fable 5 vs Mercury 2.5
Claude Fable 5 is the stronger model overall, scoring 66.8 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's lead doesn't matter for your workload.
Last verified . 4 shared benchmarks.
Summary
- They share 4 benchmarks with published results for both. Claude Fable 5 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 leads 88.5 to 23.3.
- The biggest single-benchmark swing is ProofBench: 95% for Claude Fable 5 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.
- Claude Fable 5 accepts more context: 1M tokens versus 260K.
Side by side
| Claude Fable 5 | Mercury 2.5 | |
|---|---|---|
| Provider | Anthropic | Inception |
| Noometry Index | 66.8 | 33.5 |
| Released | 2026-06-07 | 2026-09-08 |
| Weights | Proprietary | Proprietary |
| Context window | 1M | 260K |
| Max output | 128K | 66K |
| Input $ / M tokens | $10 | $0.04 |
| Output $ / M tokens | $50 | $0.15 |
| Results tracked | 62 | 4 |
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Category by category
Coding Claude Fable 5 leads
Claude Fable 5: 70.6 (#4), Mercury 2.5: 39.5 (#156)
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| SciCode | 61% | 38.5% |
| ALE-Bench | 2,041 | 301.65 |
| DeepSWE | 69.9% | — |
| FrontierCode | 53.5% | — |
| LMArena WebDev | 1625 | — |
| FrontierSWE | 47% | — |
| GSO | 78.4% | — |
| WeirdML | 91.9% | — |
| LMArena Coding | 1519 | — |
| MirrorCode | 63.9% | — |
Agentic & Tool Use Not comparable
Claude Fable 5: 54.0 (#2), Mercury 2.5: —
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| APEX-Agents | 63.6% | — |
| Remote Labor Index | 16.1% | — |
| τ²-bench Banking | 39.7% | — |
| PostTrainBench | 41.8% | — |
| GBAEval | 74.5% | — |
| GDP.pdf | 30% | — |
| LMArena Search | 1230 | — |
| Vending-Bench 2 | 5,680 | — |
Reasoning Claude Fable 5 leads
Claude Fable 5: 76.8 (#6), Mercury 2.5: 22.4 (#193)
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| CritPt | 28.6% | 0% |
| ARC-AGI-2 | 89.2% | — |
| SimpleBench | 81.9% | — |
| Kagi LLM Benchmark | 91.4% | — |
| NYT Connections (extended) | 92.7% | — |
| ARC-AGI-1 | 98.5% | — |
| Chess Puzzles | 41% | — |
| EnigmaEval | 39.3% | — |
| EBR-Bench | 39.5% | — |
| LMArena Hard Prompts | 1508 | — |
| Mystery Game Puzzles | 52% | — |
| DTBench | 98.4% | — |
| LMCA | 61.1% | — |
| Surface Evolver Bench | 95% | — |
| Bench to the Future 3 | 0.13 | — |
| Epoch Capabilities Index | 162.06 | — |
Math Claude Fable 5 leads
Claude Fable 5: 88.5 (#5), Mercury 2.5: 23.3 (#272)
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| ProofBench | 95% | 3% |
| FrontierMath (Tiers 1-3) | 87% | — |
| FrontierMath Tier 4 | 90.2% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| LMArena Math | 1519 | — |
| FrontierMath Erdős | 0% | — |
Knowledge Not comparable
Claude Fable 5: 62.2 (#25), Mercury 2.5: —
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| GPQA Diamond | 85.9% | — |
| SimpleQA Verified | 70.7% | — |
| LMArena Expert | 1534 | — |
Multimodal Not comparable
Claude Fable 5: 45.3 (#17), Mercury 2.5: —
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| LMArena Vision | 1324 | — |
| Blueprint-Bench 2 | 38.6% | — |
| Furniture Assembly | 35.8% | — |
| LMArena Document | 1496 | — |
Multilingual Not comparable
Claude Fable 5: 57.3 (#9), Mercury 2.5: —
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| LMArena Non-English | 1481 | — |
| LMArena Chinese | 1543 | — |
| LMArena French | 1505 | — |
| LMArena German | 1486 | — |
| LMArena Japanese | 1506 | — |
| LMArena Korean | 1488 | — |
| LMArena Russian | 1504 | — |
| LMArena Spanish | 1498 | — |
Instruction Following Not comparable
Claude Fable 5: 78.6 (#8), Mercury 2.5: —
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| LMArena Instruction Following | 1502 | — |
Long Context Not comparable
Claude Fable 5: 46.3 (#23), Mercury 2.5: —
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| LMArena Longer Query | 1509 | — |
Writing & Preference Not comparable
Claude Fable 5: 75.9 (#5), Mercury 2.5: —
| Benchmark | Claude Fable 5 | Mercury 2.5 |
|---|---|---|
| LMArena Text | 1491 | — |
| LMArena Creative Writing | 1494 | — |
| EQ-Bench Creative Writing | 1943 | — |
| EQ-Bench 4 | 1340 | — |
| LMArena Multi-Turn | 1504 | — |
Frequently asked questions
Is Claude Fable 5 better than Mercury 2.5?
Claude Fable 5 is the stronger model overall, scoring 66.8 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's lead doesn't matter for your workload.
Which is cheaper, Claude Fable 5 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 lists at $10 and $50.
Is Claude Fable 5 or Mercury 2.5 better for coding?
Claude Fable 5 scores higher on coding benchmarks: 70.6 versus 39.5 in the Noometry coding category.
Which has the bigger context window?
Claude Fable 5 does, with 1M tokens against 260K.
How many benchmarks do Claude Fable 5 and Mercury 2.5 share?
4 benchmarks have published results for both models. Claude Fable 5 has 62 scored results on Noometry and Mercury 2.5 has 4.