Model comparison
Claude Sonnet 5.5 vs DeepSeek V4.1 Flash
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 52.8 on the Noometry Index. DeepSeek V4.1 Flash costs 15× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Last verified . 27 shared benchmarks.
DeepSeekSummary
- They share 27 benchmarks with published results for both. Claude Sonnet 5.5 scores higher in 10 categories and DeepSeek V4.1 Flash in 0 categories; 6 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Sonnet 5.5 leads 87.9 to 66.7.
- The biggest single-benchmark swing is FrontierMath Tier 4: 80.5% for Claude Sonnet 5.5 and 26.8% for DeepSeek V4.1 Flash.
- DeepSeek V4.1 Flash is cheaper at $0.15 / $0.60 per million input/output tokens, against $2 / $10 for Claude Sonnet 5.5.
- DeepSeek V4.1 Flash has downloadable open weights; the other is API-only.
Side by side
| Claude Sonnet 5.5 | DeepSeek V4.1 Flash | |
|---|---|---|
| Provider | Anthropic | DeepSeek |
| Noometry Index | 61.9 | 52.8 |
| Released | 2026-09-28 | 2026-09-09 |
| Weights | Proprietary | Open |
| Context window | 1M | 1M |
| Max output | 128K | 393K |
| Input $ / M tokens | $2 | $0.15 |
| Output $ / M tokens | $10 | $0.60 |
| Results tracked | 32 | 37 |
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Category by category
Coding Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 67.3 (#6), DeepSeek V4.1 Flash: 52.9 (#32)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| LMArena WebDev | 1774 | 1619 |
| SciCode | 61% | 51.9% |
| LMArena Coding | 1513 | 1506 |
| ALE-Bench | 1,819 | 1,092 |
| FrontierCode | 52.1% | — |
| CursorBench | 55.5% | — |
| FrontierSWE | 61.9% | — |
Agentic & Tool Use Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 45.0 (#16), DeepSeek V4.1 Flash: 31.2 (#69)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| APEX-Agents | 75.5% | 39.5% |
| GDP.pdf | — | 19.8% |
Reasoning Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 54.0 (#28), DeepSeek V4.1 Flash: 50.2 (#36)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| NYT Connections (extended) | 80.5% | 89.6% |
| CritPt | 31.4% | 14.3% |
| LMArena Hard Prompts | 1495 | 1483 |
| Mystery Game Puzzles | 65% | 43% |
| Epoch Capabilities Index | 165.03 | 154.9 |
| DTBench | — | 89.9% |
| LMCA | — | 47% |
| Surface Evolver Bench | — | 46.3% |
Math Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 87.9 (#6), DeepSeek V4.1 Flash: 66.7 (#25)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| FrontierMath (Tiers 1-3) | 88.8% | 67.4% |
| FrontierMath Tier 4 | 80.5% | 26.8% |
| OTIS Mock AIME 2024-2025 | 100% | 98.3% |
| ProofBench | 100% | 54% |
| LMArena Math | 1510 | 1477 |
| FrontierMath Erdős | 2.9% | — |
Knowledge Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 66.0 (#12), DeepSeek V4.1 Flash: 57.9 (#38)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| GPQA Diamond | 95.6% | 89.8% |
| LMArena Expert | 1540 | 1506 |
| SimpleQA Verified | 46.5% | — |
Multimodal Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 51.5 (#6), DeepSeek V4.1 Flash: 39.1 (#61)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| LMArena Vision | 1289 | 1277 |
| Furniture Assembly | 75% | 34.2% |
Multilingual Too close to call
Claude Sonnet 5.5: 55.3 (#30), DeepSeek V4.1 Flash: 55.0 (#35)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| LMArena Non-English | 1452 | 1448 |
| LMArena Chinese | 1522 | 1497 |
| LMArena Russian | 1451 | 1471 |
| LMArena French | — | 1452 |
| LMArena German | — | 1484 |
| LMArena Japanese | — | 1412 |
| LMArena Korean | — | 1452 |
| LMArena Spanish | — | 1459 |
Instruction Following Too close to call
Claude Sonnet 5.5: 78.3 (#11), DeepSeek V4.1 Flash: 77.3 (#26)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| LMArena Instruction Following | 1495 | 1474 |
Long Context Too close to call
Claude Sonnet 5.5: 45.9 (#28), DeepSeek V4.1 Flash: 45.2 (#47)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| LMArena Longer Query | 1498 | 1475 |
Writing & Preference Too close to call
Claude Sonnet 5.5: 66.0 (#40), DeepSeek V4.1 Flash: 65.4 (#48)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| LMArena Text | 1471 | 1462 |
| LMArena Creative Writing | 1465 | 1435 |
| LMArena Multi-Turn | 1474 | 1457 |
| EQ-Bench Creative Writing | — | 1540 |
Frequently asked questions
Is Claude Sonnet 5.5 better than DeepSeek V4.1 Flash?
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 52.8 on the Noometry Index. DeepSeek V4.1 Flash costs 15× 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 DeepSeek V4.1 Flash?
DeepSeek V4.1 Flash is cheaper. It lists at $0.15 per million input tokens and $0.60 per million output tokens; Claude Sonnet 5.5 lists at $2 and $10.
Is Claude Sonnet 5.5 or DeepSeek V4.1 Flash better for coding?
Claude Sonnet 5.5 scores higher on coding benchmarks: 67.3 versus 52.9 in the Noometry coding category.
Which has the bigger context window?
Both accept 1M tokens.
How many benchmarks do Claude Sonnet 5.5 and DeepSeek V4.1 Flash share?
27 benchmarks have published results for both models. Claude Sonnet 5.5 has 32 scored results on Noometry and DeepSeek V4.1 Flash has 37.