Claude Sonnet 5.5 vs DeepSeek V4 Flash 0731
Claude Sonnet 5.5 leads DeepSeek V4 Flash 0731 on coding, 87.3 to 51.8 on the Vibe Coding Index, and DeepSeek V4 Flash 0731 costs 25.3x less per output token ($0.396 vs $10.00 per million). Updated October 22, 2026; 38 benchmarks have a result for both.
Claude Sonnet 5.5 or DeepSeek V4 Flash 0731: which to pick
Pick Claude Sonnet 5.5 for coding: it scores 87.3 on the Vibe Coding Index against 51.8 for DeepSeek V4 Flash 0731.
Pick DeepSeek V4 Flash 0731 for output tokens 25.3x cheaper ($0.396 vs $10.00 per million) and a larger context window (1.05M against 1M tokens).
- Shared results
- 38
- Claude Sonnet 5.5 only
- 58
- DeepSeek V4 Flash 0731 only
- 17
- Like-for-like categories
- 8 of 9
Only benchmarks that tested both models count toward a pick; a result only one model has is shown but not compared.
Which one for your work
Each card is decided by one number both models carry. Where only one has it, the card says so and makes no call.
Coding
Vibe Coding Index, six public coding benchmarks
Claude Sonnet 5.5
Claude Sonnet 5.5 scores 87.3 against 51.8.
5 and 4 benchmarks behind the scores
Intelligence
AA Intelligence Index
Claude Sonnet 5.5
Claude Sonnet 5.5 leads, 56.0 against 34.3.
Same board, both measured
Agentic work
AA Agentic Index
No call
Only DeepSeek V4 Flash 0731 has a AA Agentic Index result, 41.0.
Directional only
Reasoning
GPQA Diamond
No call
Only DeepSeek V4 Flash 0731 has a GPQA Diamond result, 89.9%.
Directional only
Knowledge
MMLU Pro
No call
Only DeepSeek V4 Flash 0731 has a MMLU Pro result, 86.2%.
Directional only
Web design
Design Arena: websites
Claude Sonnet 5.5
Claude Sonnet 5.5 leads, 1326 against 1237.
Same board, both measured
General
Vals Index
No call
Only Claude Sonnet 5.5 has a Vals Index result, 70.8%.
Directional only
Long documents
Listed context window
DeepSeek V4 Flash 0731
DeepSeek V4 Flash 0731 takes 1.05M tokens against 1M.
Listed by OpenRouter
Everyday cost
1K input + 500 output tokens
DeepSeek V4 Flash 0731
Claude Sonnet 5.5 $0.0070, DeepSeek V4 Flash 0731 $0.0003 per turn.
List prices
Cost per solved task
One SWE-bench Verified task, solved
No call
Only DeepSeek V4 Flash 0731 has the number, $0.01.
Directional only
At a glance
- Coding index
- Claude Sonnet 5.5 87.3 from 5 benchmarks, DeepSeek V4 Flash 0731 51.8 from 4 benchmarks.
- Widest category
- Math, 34.2 points apart on average over 4 shared benchmarks.
- Widest single gap
- Terminal-Bench 4 (Vals AI): Claude Sonnet 5.5 64.1% against DeepSeek V4 Flash 0731 18.7%, 60.6 points apart on a 0 to 100 scale.
- Output price
- Claude Sonnet 5.5 $10.00 against DeepSeek V4 Flash 0731 $0.396 per million output tokens, 25.3x apart.
- Context window
- Claude Sonnet 5.5 takes 1M tokens, DeepSeek V4 Flash 0731 1.05M.
Benchmark by benchmark
First the score: boards each model leads, per category, where both have a result. Then every board, a category to a fold; bars are each result on a 0 to 100 scale, so compare the two in a row, not one row with another.
| Category | Claude Sonnet 5.5 | Bars | DeepSeek V4 Flash 0731 | Ties |
|---|---|---|---|---|
| Coding | 9 | 1 | ||
| Intelligence | 2 | 0 | ||
| Agentic work | 6 | 0 | ||
| Reasoning | 4 | 0 | ||
| Math | 4 | 0 | ||
| Knowledge | 2 | 0 | ||
| Web design | 6 | 0 | ||
| General | 4 | 0 | ||
| All shared boards | 37 | 1 |
CodingLike-for-likeSix of these boards feed the Vibe Coding Index91
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| LiveBench coding | 94.7% | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena WebDev | 1768 | Not measured | Only Claude Sonnet 5.5 measured |
| AA Coding Index | Not measured | 69.1 | Only DeepSeek V4 Flash 0731 measured |
| LiveCodeBench (Vals AI) | Not measured | 87.3% | Only DeepSeek V4 Flash 0731 measured |
| SWE-bench Verified (Vals AI) | Not measured | 88.8% | Only DeepSeek V4 Flash 0731 measured |
| Terminal-Bench 4 (Vals AI) | 64.1% | 18.7% | Claude Sonnet 5.5 |
| Vibe Code Bench (Vals AI) | 92.4% | 74.7% | Claude Sonnet 5.5 |
| Code migration (Vals AI) | 69.8% | 38.6% | Claude Sonnet 5.5 |
| ProgramBench (Vals AI) | 6.5% | 0.0% | Claude Sonnet 5.5 |
| IOI (Vals AI) | 83.1% | 32.7% | Claude Sonnet 5.5 |
| Terminal-Bench 2.1 (Vals AI) | 83.2% | 67.0% | Claude Sonnet 5.5 |
| SWE-bench Multimodal (Vals AI) | 58.3% | Not measured | Only Claude Sonnet 5.5 measured |
| SkillsBench (Vals AI) | Not measured | 50.7% | Only DeepSeek V4 Flash 0731 measured |
| CyberBench (Vals AI) | 59.6% | 72.1% | DeepSeek V4 Flash 0731 |
| SciCode | 61.0% | 50.3% | Claude Sonnet 5.5 |
| FrontierCode | 52.1% | 18.8% | Claude Sonnet 5.5 |
| FrontierSWE | 61.9% | Not measured | Only Claude Sonnet 5.5 measured |
| WeirdML | Not measured | 63.0% | Only DeepSeek V4 Flash 0731 measured |
| ALE-Bench | 1819.1 | 1306.1 | Claude Sonnet 5.5 |
| LMArena Text: coding | 1513 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: software and IT | 1504 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena WebDev: React | 1817 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena WebDev: HTML | 1741 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena WebDev: from an image | 1737 | Not measured | Only Claude Sonnet 5.5 measured |
| SciCode | 13.8% | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 14 boards here | |||
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index20
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| AA Intelligence Index | 56.0 | 34.3 | Claude Sonnet 5.5 |
| Epoch Capabilities Index | 166.2 | 154.8 | Claude Sonnet 5.5 |
Agentic workLike-for-likePublic boards, shown as published, kept out of the index60
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| AA Agentic Index | Not measured | 41.0 | Only DeepSeek V4 Flash 0731 measured |
| Design Arena: agents building web apps | 1305 | Not measured | Only Claude Sonnet 5.5 measured |
| Design Arena: agents building mobile apps | 1260 | Not measured | Only Claude Sonnet 5.5 measured |
| Design Arena: spreadsheets | 1260 | Not measured | Only Claude Sonnet 5.5 measured |
| LiveBench research | 83.6% | Not measured | Only Claude Sonnet 5.5 measured |
| LiveBench browser | 84.0% | Not measured | Only Claude Sonnet 5.5 measured |
| LiveBench long agentic | 78.8% | Not measured | Only Claude Sonnet 5.5 measured |
| SREBench (Vals AI) | 30.1% | Not measured | Only Claude Sonnet 5.5 measured |
| Finance Agent (Vals AI) | 58.1% | 49.5% | Claude Sonnet 5.5 |
| Tax Agent Bench (Vals AI) | 42.0% | 28.1% | Claude Sonnet 5.5 |
| Legal Research Bench (Vals AI) | 48.1% | 30.3% | Claude Sonnet 5.5 |
| Harvey's Legal Agent Benchmark (Vals AI) | 10.4% | Not measured | Only Claude Sonnet 5.5 measured |
| Excel Modeling Benchmark (Vals AI) | 75.7% | 57.0% | Claude Sonnet 5.5 |
| BioMysteryBench (Vals AI) | 81.1% | 64.4% | Claude Sonnet 5.5 |
| Terminal-Bench-Science (Vals AI) | 47.1% | 4.3% | Claude Sonnet 5.5 |
| Vals Science Index | 59.1% | Not measured | Only Claude Sonnet 5.5 measured |
| APEX-Agents | 75.5% | Not measured | Only Claude Sonnet 5.5 measured |
| SpireClimb | 1.3% | Not measured | Only Claude Sonnet 5.5 measured |
| Vending-Bench 2 | $11,165 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 22 boards here | |||
ReasoningLike-for-likePublic boards, shown as published, kept out of the index40
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| GPQA Diamond | Not measured | 89.9% | Only DeepSeek V4 Flash 0731 measured |
| LiveBench reasoning | 91.6% | Not measured | Only Claude Sonnet 5.5 measured |
| MysteryMechanism (Vals AI) | 49.1% | Not measured | Only Claude Sonnet 5.5 measured |
| GPQA Diamond (Artificial Analysis run) | Not measured | 90.8% | Only DeepSeek V4 Flash 0731 measured |
| Humanity's Last Exam (Artificial Analysis run) | 55.0% | 38.6% | Claude Sonnet 5.5 |
| GPQA Diamond (Epoch AI run) | 95.6% | 91.0% | Claude Sonnet 5.5 |
| ARC-AGI | Not measured | 89.0% | Only DeepSeek V4 Flash 0731 measured |
| ARC-AGI-2 | Not measured | 61.4% | Only DeepSeek V4 Flash 0731 measured |
| SimpleBench | Not measured | 61.1% | Only DeepSeek V4 Flash 0731 measured |
| Chess puzzles | 59.0% | 32.0% | Claude Sonnet 5.5 |
| Mystery game puzzles | 65.0% | 34.0% | Claude Sonnet 5.5 |
| LMArena Text: hard prompts | 1494 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: expert | 1531 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: hard prompts in English | 1502 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: diagrams | 1329 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: homework | 1331 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 6 boards here | |||
MathLike-for-likePublic boards, shown as published, kept out of the index40
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| OTIS Mock AIME | 100.0% | 94.4% | Claude Sonnet 5.5 |
| FrontierMath, tiers 1 to 3 | 88.8% | 57.5% | Claude Sonnet 5.5 |
| FrontierMath, tier 4 | 80.5% | 24.4% | Claude Sonnet 5.5 |
| ProofBench | 100.0% | 56.0% | Claude Sonnet 5.5 |
| LMArena Text: math | 1497 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: mathematical work | 1510 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 7 boards here | |||
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index20
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| MMLU Pro | Not measured | 86.2% | Only DeepSeek V4 Flash 0731 measured |
| LegalBench (Vals AI) | Not measured | 77.7% | Only DeepSeek V4 Flash 0731 measured |
| CorpFin (Vals AI) | Not measured | 61.9% | Only DeepSeek V4 Flash 0731 measured |
| TaxEval (Vals AI) | Not measured | 70.7% | Only DeepSeek V4 Flash 0731 measured |
| MedCode (Vals AI) | 52.9% | 41.4% | Claude Sonnet 5.5 |
| SimpleQA Verified | 46.5% | 33.6% | Claude Sonnet 5.5 |
| LMArena Text: science | 1483 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: medicine and healthcare | 1464 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: legal and government | 1483 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: business and finance | 1468 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 8 boards here | |||
Web designLike-for-likePublic boards, shown as published, kept out of the index60
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| Design Arena: websites | 1326 | 1237 | Claude Sonnet 5.5 |
| Design Arena: UI components | 1368 | 1233 | Claude Sonnet 5.5 |
| Design Arena: game dev | 1471 | 1207 | Claude Sonnet 5.5 |
| Design Arena: data viz | 1392 | 1180 | Claude Sonnet 5.5 |
| Design Arena: 3D | 1445 | 1208 | Claude Sonnet 5.5 |
| Design Arena: all code categories | 1364 | 1229 | Claude Sonnet 5.5 |
| Design Arena: SVG | Not measured | 1184 | Only DeepSeek V4 Flash 0731 measured |
| Design Arena: ASCII art | Not measured | 1090 | Only DeepSeek V4 Flash 0731 measured |
| LiveBench design | 85.0% | Not measured | Only Claude Sonnet 5.5 measured |
GeneralLike-for-likePublic boards, shown as published, kept out of the index40
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| Vals Index | 70.8% | Not measured | Only Claude Sonnet 5.5 measured |
| LiveBench data analysis | 59.5% | Not measured | Only Claude Sonnet 5.5 measured |
| Public Benefits Bench (Vals AI) | 67.2% | Not measured | Only Claude Sonnet 5.5 measured |
| SAGE (Vals AI) | 51.8% | Not measured | Only Claude Sonnet 5.5 measured |
| MedScribe (Vals AI) | 91.1% | 80.4% | Claude Sonnet 5.5 |
| Long context reasoning (AA-LCR) | 82.7% | 79.7% | Claude Sonnet 5.5 |
| DTBench | 97.3% | 90.9% | Claude Sonnet 5.5 |
| LMCA | 68.3% | 41.7% | Claude Sonnet 5.5 |
| Furniture assembly | 75.0% | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text | 1473 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: instruction following | 1492 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: creative writing | 1467 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision | 1287 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: English | 1484 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: non-English | 1456 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: Chinese | 1535 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: French | 1499 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: Spanish | 1451 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: Russian | 1454 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: multi-turn | 1465 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: longer queries | 1495 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: writing and language | 1474 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Text: entertainment and media | 1461 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: English | 1289 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: reading text | 1297 | Not measured | Only Claude Sonnet 5.5 measured |
| LMArena Vision: creative writing | 1242 | Not measured | Only Claude Sonnet 5.5 measured |
| Neither model has a result on the other 20 boards here | |||
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 | Leader |
|---|---|---|---|
| Neither model has a result on 5 boards here | |||
What each workload costs
Three fixed token mixes at each model's listed price, so per-token rates become a bill.
Chat turn
1K input + 500 output tokens
DeepSeek V4 Flash 0731 costs less
Repository review
50K input + 3K output tokens
DeepSeek V4 Flash 0731 costs less
Agent loop
200K input + 10K output tokens
DeepSeek V4 Flash 0731 costs less
Listed OpenRouter rates, without cache or batch discounts. A workload that does not fit a model's context window would need splitting.
Specification differences
The leading value in a row is marked; a row with a missing value names no leader. Our two rows are marked in red.
| Specification | Anthropic Claude Sonnet 5.5 | DeepSeek V4 Flash 0731 |
|---|---|---|
| Maker | Anthropic | DeepSeek |
| Weights | No public weights listed | Open weights |
| Released | September 28, 2026 | July 31, 2026 |
| Context window | 1M | 1.05M |
| Input $/Mtok | $2.00 | $0.14 |
| Output $/Mtok | $10.00 | $0.396 |
| Coding index | 87.3 | 51.8 |
| Independent measurements behind it | 5 | 4 |
| Cost per solved task | Not computable | $0.01 |
| Source | OpenRouter listing | OpenRouter listing |
Questions
Is Claude Sonnet 5.5 better than DeepSeek V4 Flash 0731 for coding?
Pick Claude Sonnet 5.5 for coding: it scores 87.3 on the Vibe Coding Index against 51.8 for DeepSeek V4 Flash 0731. Pick DeepSeek V4 Flash 0731 for output tokens 25.3x cheaper ($0.396 vs $10.00 per million) and a larger context window (1.05M against 1M tokens).
Which is cheaper, Claude Sonnet 5.5 or DeepSeek V4 Flash 0731?
Claude Sonnet 5.5 costs $2.00 per million input tokens and $10.00 per million output tokens; DeepSeek V4 Flash 0731 costs $0.14 and $0.396. Cost per solved task is known for DeepSeek V4 Flash 0731 only.
Which has the bigger context window, Claude Sonnet 5.5 or DeepSeek V4 Flash 0731?
DeepSeek V4 Flash 0731, with 1.05M tokens against 1M.
How many benchmarks is the Claude Sonnet 5.5 vs DeepSeek V4 Flash 0731 comparison based on?
38 benchmarks have a result for both models as of October 22, 2026. Claude Sonnet 5.5's coding index rests on 5 independent benchmarks and DeepSeek V4 Flash 0731's on 4. Where only one model has a result, the page says so instead of naming a winner.