Model comparison
Claude Opus 5.5 vs Mercury 2
Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 39.1 on the Noometry Index. Mercury 2 costs 21× less per token, which makes it the better buy when Claude Opus 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 Opus 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 reasoning, where Claude Opus 5.5 leads 80.2 to 23.8.
- The biggest single-benchmark swing is CritPt: 31.7% for Claude Opus 5.5 and 0.8% for Mercury 2.
- Mercury 2 is cheaper at $0.25 / $0.75 per million input/output tokens, against $4 / $20 for Claude Opus 5.5.
- Claude Opus 5.5 accepts more context: 1M tokens versus 128K.
Side by side
| Claude Opus 5.5 | Mercury 2 | |
|---|---|---|
| Provider | Anthropic | Inception |
| Noometry Index | 68.6 | 39.1 |
| Released | 2026-09-22 | 2026-02-20 |
| Weights | Proprietary | Proprietary |
| Context window | 1M | 128K |
| Max output | 128K | 50K |
| Input $ / M tokens | $4 | $0.25 |
| Output $ / M tokens | $20 | $0.75 |
| Results tracked | 44 | 17 |
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Category by category
Coding Claude Opus 5.5 leads
Claude Opus 5.5: 71.9 (#3), Mercury 2: 33.5 (#255)
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| LMArena WebDev | 1813 | 1171 |
| SciCode | 66.9% | 38.7% |
| LMArena Coding | 1547 | 1391 |
| ALE-Bench | 2,147 | 785.58 |
| FrontierCode | 54.6% | — |
| CursorBench | 57.8% | — |
| FrontierSWE | 62.3% | — |
| WeirdML | — | 43.2% |
| MirrorCode | 77.4% | — |
Agentic & Tool Use Not comparable
Claude Opus 5.5: 45.3 (#15), Mercury 2: —
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| APEX-Agents | 73.5% | — |
| GDP.pdf | 30.6% | — |
| Vending-Bench 2 | 9,235 | — |
Reasoning Claude Opus 5.5 leads
Claude Opus 5.5: 80.2 (#3), Mercury 2: 23.8 (#170)
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| CritPt | 31.7% | 0.8% |
| LMArena Hard Prompts | 1535 | 1362 |
| ARC-AGI-2 | 93.3% | — |
| NYT Connections (extended) | 88.5% | — |
| ARC-AGI-1 | 98.5% | — |
| EBR-Bench | 71.4% | — |
| Mystery Game Puzzles | 71% | — |
| DTBench | 98.9% | — |
| LMCA | 68.2% | — |
| Epoch Capabilities Index | 167.33 | — |
Math Not comparable
Claude Opus 5.5: 91.8 (#3), Mercury 2: —
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| FrontierMath (Tiers 1-3) | 91.2% | — |
| FrontierMath Tier 4 | 95% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| ProofBench | 100% | — |
| LMArena Math | 1506 | — |
| FrontierMath Erdős | 2.9% | — |
Knowledge Claude Opus 5.5 leads
Claude Opus 5.5: 66.4 (#10), Mercury 2: 36.2 (#172)
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| LMArena Expert | 1547 | 1358 |
| GPQA Diamond | 90.6% | — |
| SimpleQA Verified | 72.2% | — |
| Vectara Hallucination Rate | — | 12.3% |
Multimodal Not comparable
Claude Opus 5.5: 57.8 (#1), Mercury 2: —
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| LMArena Vision | 1321 | — |
| Blueprint-Bench 2 | 51.2% | — |
| Furniture Assembly | 83.3% | — |
Multilingual Claude Opus 5.5 leads
Claude Opus 5.5: 59.1 (#2), Mercury 2: 46.6 (#157)
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| LMArena Non-English | 1507 | 1331 |
| LMArena Chinese | 1588 | 1417 |
| LMArena Russian | 1520 | 1304 |
| LMArena French | 1514 | — |
| LMArena Spanish | 1507 | — |
Instruction Following Claude Opus 5.5 leads
Claude Opus 5.5: 80.0 (#3), Mercury 2: 70.2 (#165)
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| LMArena Instruction Following | 1537 | 1329 |
Long Context Claude Opus 5.5 leads
Claude Opus 5.5: 47.1 (#19), Mercury 2: 40.5 (#154)
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| LMArena Longer Query | 1532 | 1330 |
Writing & Preference Claude Opus 5.5 leads
Claude Opus 5.5: 78.2 (#3), Mercury 2: 53.8 (#155)
| Benchmark | Claude Opus 5.5 | Mercury 2 |
|---|---|---|
| LMArena Text | 1515 | 1355 |
| LMArena Creative Writing | 1533 | 1289 |
| LMArena Multi-Turn | 1499 | 1358 |
| EQ-Bench Creative Writing | 2050 | — |
Frequently asked questions
Is Claude Opus 5.5 better than Mercury 2?
Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 39.1 on the Noometry Index. Mercury 2 costs 21× less per token, which makes it the better buy when Claude Opus 5.5's lead doesn't matter for your workload.
Which is cheaper, Claude Opus 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 Opus 5.5 lists at $4 and $20.
Is Claude Opus 5.5 or Mercury 2 better for coding?
Claude Opus 5.5 scores higher on coding benchmarks: 71.9 versus 33.5 in the Noometry coding category.
Which has the bigger context window?
Claude Opus 5.5 does, with 1M tokens against 128K.
How many benchmarks do Claude Opus 5.5 and Mercury 2 share?
15 benchmarks have published results for both models. Claude Opus 5.5 has 44 scored results on Noometry and Mercury 2 has 17.