Model comparison
Claude Sonnet 5.5 vs Mercury 2
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 39.1 on the Noometry Index. Mercury 2 costs 11× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Last verified . 15 shared benchmarks.
Summary
- They share 15 benchmarks with published results for both. Claude Sonnet 5.5 scores higher in 7 categories and Mercury 2 in 0 categories; 7 gaps are clear of the uncertainty.
- The widest gap is in coding, where Claude Sonnet 5.5 leads 67.3 to 33.5.
- The biggest single-benchmark swing is CritPt: 31.4% for Claude Sonnet 5.5 and 0.8% for Mercury 2.
- Mercury 2 is cheaper at $0.25 / $0.75 per million input/output tokens, against $2 / $10 for Claude Sonnet 5.5.
- Claude Sonnet 5.5 accepts more context: 1M tokens versus 128K.
Side by side
| Claude Sonnet 5.5 | Mercury 2 | |
|---|---|---|
| Provider | Anthropic | Inception |
| Noometry Index | 61.9 | 39.1 |
| Released | 2026-09-28 | 2026-02-20 |
| Weights | Proprietary | Proprietary |
| Context window | 1M | 128K |
| Max output | 128K | 50K |
| Input $ / M tokens | $2 | $0.25 |
| Output $ / M tokens | $10 | $0.75 |
| Results tracked | 32 | 17 |
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Category by category
Coding Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 67.3 (#6), Mercury 2: 33.5 (#255)
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| LMArena WebDev | 1774 | 1171 |
| SciCode | 61% | 38.7% |
| LMArena Coding | 1513 | 1391 |
| ALE-Bench | 1,819 | 785.58 |
| FrontierCode | 52.1% | — |
| CursorBench | 55.5% | — |
| FrontierSWE | 61.9% | — |
| WeirdML | — | 43.2% |
Agentic & Tool Use Not comparable
Claude Sonnet 5.5: 45.0 (#16), Mercury 2: —
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| APEX-Agents | 75.5% | — |
Reasoning Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 54.0 (#28), Mercury 2: 23.8 (#170)
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| CritPt | 31.4% | 0.8% |
| LMArena Hard Prompts | 1495 | 1362 |
| NYT Connections (extended) | 80.5% | — |
| Mystery Game Puzzles | 65% | — |
| Epoch Capabilities Index | 165.03 | — |
Math Not comparable
Claude Sonnet 5.5: 87.9 (#6), Mercury 2: —
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| FrontierMath (Tiers 1-3) | 88.8% | — |
| FrontierMath Tier 4 | 80.5% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| ProofBench | 100% | — |
| LMArena Math | 1510 | — |
| FrontierMath Erdős | 2.9% | — |
Knowledge Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 66.0 (#12), Mercury 2: 36.2 (#172)
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| LMArena Expert | 1540 | 1358 |
| GPQA Diamond | 95.6% | — |
| SimpleQA Verified | 46.5% | — |
| Vectara Hallucination Rate | — | 12.3% |
Multimodal Not comparable
Claude Sonnet 5.5: 51.5 (#6), Mercury 2: —
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| LMArena Vision | 1289 | — |
| Furniture Assembly | 75% | — |
Multilingual Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 55.3 (#30), Mercury 2: 46.6 (#157)
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| LMArena Non-English | 1452 | 1331 |
| LMArena Chinese | 1522 | 1417 |
| LMArena Russian | 1451 | 1304 |
Instruction Following Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 78.3 (#11), Mercury 2: 70.2 (#165)
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| LMArena Instruction Following | 1495 | 1329 |
Long Context Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 45.9 (#28), Mercury 2: 40.5 (#154)
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| LMArena Longer Query | 1498 | 1330 |
Writing & Preference Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 66.0 (#40), Mercury 2: 53.8 (#155)
| Benchmark | Claude Sonnet 5.5 | Mercury 2 |
|---|---|---|
| LMArena Text | 1471 | 1355 |
| LMArena Creative Writing | 1465 | 1289 |
| LMArena Multi-Turn | 1474 | 1358 |
Frequently asked questions
Is Claude Sonnet 5.5 better than Mercury 2?
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 39.1 on the Noometry Index. Mercury 2 costs 11× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Which is cheaper, Claude Sonnet 5.5 or Mercury 2?
Mercury 2 is cheaper. It lists at $0.25 per million input tokens and $0.75 per million output tokens; Claude Sonnet 5.5 lists at $2 and $10.
Is Claude Sonnet 5.5 or Mercury 2 better for coding?
Claude Sonnet 5.5 scores higher on coding benchmarks: 67.3 versus 33.5 in the Noometry coding category.
Which has the bigger context window?
Claude Sonnet 5.5 does, with 1M tokens against 128K.
How many benchmarks do Claude Sonnet 5.5 and Mercury 2 share?
15 benchmarks have published results for both models. Claude Sonnet 5.5 has 32 scored results on Noometry and Mercury 2 has 17.