In short
How they differ.
Worked out from the figures below. Prices and specs are the makers' own, read Oct 20, 2026.
- DeepSeek-V4.1-Flash-1017 is cheaper per output token: $1.20 against $10 per million tokens, so Claude Sonnet 5.5 costs 8.3 times as much.
- DeepSeek-V4.1-Flash-1017 can be downloaded and run on your own machine; Claude Sonnet 5.5 can't.
- On the 3 independent boards that rank both, Claude Sonnet 5.5 places higher on 3 and DeepSeek-V4.1-Flash-1017 on 0.
Side by side
The specs.
| Claude Sonnet 5.5 | DeepSeek-V4.1-Flash-1017 | |
|---|---|---|
| Made by | Anthropic · US | DeepSeek · China |
| Released | Sep 28, 2026 | Oct 17, 2026 |
| Price per 1M tokens | $2 in / $10 out | $0.30 in / $1.20 out (peak-hours price) |
| Context window | 1M | 1M |
| Takes in | text, image | text, image |
| Download and run it yourself | No | Yes (MIT) |
| Size | Not published | 552B backbone parameters parameters, 8B per token during prefill, 16B during decode active |
| Maker says | “High-performance model for coding and agents” | “Stronger benchmark performance, faster task completion, and shorter outputs than the previous version.” |
| Sources | Prices, Oct 20, 2026 · Description | Prices, Oct 20, 2026 · Description |
Independent tests
Where they place.
Position on each board we follow (1 is best). Epoch AI's and Vectara's scores are shown; the other boards are linked for their own figures.
| Board | Claude Sonnet 5.5 | DeepSeek-V4.1-Flash-1017 |
|---|---|---|
| Epoch Capabilities IndexEpoch AI, Oct 20, 2026 | #6164.45 | Not listed |
| LMArena WebDevLMArena, Oct 19, 2026 | #3 | Not listed |
| LMArena mathLMArena, Oct 15, 2026 | #15 | Not listed |
| LMArena Agent ArenaLMArena, Oct 19, 2026 | #5 | Not listed |
| Humanity's Last ExamScale AI | #6 | Not listed |
| SWE-Bench ProScale AI, Sep 22, 2026 | #8 | Not listed |
| Vals IndexVals AI, Oct 19, 2026 | #1 | #8 |
| Terminal-Bench 4.0Vals AI, Oct 19, 2026 | #2 | #17 |
| Vibe Code BenchVals AI, Oct 18, 2026 | #1 | #11 |
| ProofBenchVals AI, Oct 12, 2026 | #1 | Not listed |
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