Model comparison
Claude 2.1 vs Claude Opus 5.5
Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 25.2 on the Noometry Index.
Last verified . 4 shared benchmarks.
Summary
- They share 4 benchmarks with published results for both. Claude 2.1 scores higher in 0 categories and Claude Opus 5.5 in 4 categories; 4 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Opus 5.5 leads 91.8 to 10.2.
- The biggest single-benchmark swing is OTIS Mock AIME 2024-2025: 1.9% for Claude 2.1 and 100% for Claude Opus 5.5.
Side by side
| Claude 2.1 | Claude Opus 5.5 | |
|---|---|---|
| Provider | Anthropic | Anthropic |
| Noometry Index | 25.2 | 68.6 |
| Released | 2023-11-21 | 2026-09-22 |
| Weights | Proprietary | Proprietary |
| Context window | — | 1M |
| Max output | — | 128K |
| Input $ / M tokens | — | $4 |
| Output $ / M tokens | — | $20 |
| Results tracked | 7 | 44 |
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Category by category
Coding Claude Opus 5.5 leads
Claude 2.1: 26.2 (#327), Claude Opus 5.5: 71.9 (#3)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| FrontierCode | — | 54.6% |
| CursorBench | — | 57.8% |
| LMArena WebDev | — | 1813 |
| FrontierSWE | — | 62.3% |
| SciCode | — | 66.9% |
| WeirdML | 7.1% | — |
| LMArena Coding | — | 1547 |
| MirrorCode | — | 77.4% |
| ALE-Bench | — | 2,147 |
Agentic & Tool Use Not comparable
Claude 2.1: —, Claude Opus 5.5: 45.3 (#15)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| APEX-Agents | — | 73.5% |
| GDP.pdf | — | 30.6% |
| Vending-Bench 2 | — | 9,235 |
Reasoning Claude Opus 5.5 leads
Claude 2.1: 21.4 (#221), Claude Opus 5.5: 80.2 (#3)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| DTBench | 51% | 98.9% |
| Epoch Capabilities Index | 119.27 | 167.33 |
| ARC-AGI-2 | — | 93.3% |
| NYT Connections (extended) | — | 88.5% |
| ARC-AGI-1 | — | 98.5% |
| CritPt | — | 31.7% |
| EBR-Bench | — | 71.4% |
| LMArena Hard Prompts | — | 1535 |
| Mystery Game Puzzles | — | 71% |
| LMCA | — | 68.2% |
| ForecastBench | 54.2 | — |
Math Claude Opus 5.5 leads
Claude 2.1: 10.2 (#315), Claude Opus 5.5: 91.8 (#3)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| OTIS Mock AIME 2024-2025 | 1.9% | 100% |
| FrontierMath (Tiers 1-3) | — | 91.2% |
| FrontierMath Tier 4 | — | 95% |
| ProofBench | — | 100% |
| LMArena Math | — | 1506 |
| FrontierMath Erdős | — | 2.9% |
Knowledge Claude Opus 5.5 leads
Claude 2.1: 15.4 (#292), Claude Opus 5.5: 66.4 (#10)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| GPQA Diamond | 33% | 90.6% |
| SimpleQA Verified | — | 72.2% |
| LMArena Expert | — | 1547 |
| MMLU | 73.5% | — |
Multimodal Not comparable
Claude 2.1: —, Claude Opus 5.5: 57.8 (#1)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| LMArena Vision | — | 1321 |
| Blueprint-Bench 2 | — | 51.2% |
| Furniture Assembly | — | 83.3% |
Multilingual Not comparable
Claude 2.1: —, Claude Opus 5.5: 59.1 (#2)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| LMArena Non-English | — | 1507 |
| LMArena Chinese | — | 1588 |
| LMArena French | — | 1514 |
| LMArena Russian | — | 1520 |
| LMArena Spanish | — | 1507 |
Instruction Following Not comparable
Claude 2.1: —, Claude Opus 5.5: 80.0 (#3)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| LMArena Instruction Following | — | 1537 |
Long Context Not comparable
Claude 2.1: —, Claude Opus 5.5: 47.1 (#19)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| LMArena Longer Query | — | 1532 |
Writing & Preference Not comparable
Claude 2.1: —, Claude Opus 5.5: 78.2 (#3)
| Benchmark | Claude 2.1 | Claude Opus 5.5 |
|---|---|---|
| LMArena Text | — | 1515 |
| LMArena Creative Writing | — | 1533 |
| EQ-Bench Creative Writing | — | 2050 |
| LMArena Multi-Turn | — | 1499 |
Frequently asked questions
Is Claude 2.1 better than Claude Opus 5.5?
Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 25.2 on the Noometry Index.
Is Claude 2.1 or Claude Opus 5.5 better for coding?
Claude Opus 5.5 scores higher on coding benchmarks: 71.9 versus 26.2 in the Noometry coding category.
How many benchmarks do Claude 2.1 and Claude Opus 5.5 share?
4 benchmarks have published results for both models. Claude 2.1 has 7 scored results on Noometry and Claude Opus 5.5 has 44.