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 $20 per million tokens, so Claude Opus 5.5 costs 16.7 times as much.
- DeepSeek-V4.1-Flash-1017 can be downloaded and run on your own machine; Claude Opus 5.5 can't.
- On the 3 independent boards that rank both, Claude Opus 5.5 places higher on 3 and DeepSeek-V4.1-Flash-1017 on 0.
Side by side
The specs.
| Claude Opus 5.5 | DeepSeek-V4.1-Flash-1017 | |
|---|---|---|
| Made by | Anthropic · US | DeepSeek · China |
| Released | Sep 22, 2026 | Oct 17, 2026 |
| Price per 1M tokens | $4 in / $20 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 | “For long-running agentic coding and knowledge work” | “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 Opus 5.5 | DeepSeek-V4.1-Flash-1017 |
|---|---|---|
| Epoch Capabilities IndexEpoch AI, Oct 20, 2026 | #1166.82 | Not listed |
| LMArena textLMArena, Oct 15, 2026 | #3 | Not listed |
| LMArena creative writingLMArena, Oct 15, 2026 | #1 | Not listed |
| LMArena coding chatsLMArena, Oct 15, 2026 | #6 | Not listed |
| LMArena WebDevLMArena, Oct 19, 2026 | #1 | Not listed |
| LMArena mathLMArena, Oct 15, 2026 | #14 | Not listed |
| LMArena visionLMArena, Oct 19, 2026 | #10 | Not listed |
| LMArena Agent ArenaLMArena, Oct 19, 2026 | #1 | Not listed |
| Humanity's Last ExamScale AI | #2 | Not listed |
| Remote Labor IndexScale AI | #1 | Not listed |
| Vals IndexVals AI, Oct 19, 2026 | #2 | #8 |
| Terminal-Bench 4.0Vals AI, Oct 19, 2026 | #1 | #17 |
| Vibe Code BenchVals AI, Oct 18, 2026 | #5 | #11 |
| ProofBenchVals AI, Oct 12, 2026 | #2 | Not listed |
| CUA-bench (games)Vals AI, Oct 13, 2026 | #2 | Not listed |
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