Claude Sonnet 5.5 vs DeepSeek V4.1 Flash.
Verdict by category, tale of the tape, shared benchmarks only, and cost at three workloads — all from the tracked data.
Verdict by category
| Category | Claude Sonnet 5.5 | DeepSeek V4.1 Flash | Winner |
|---|---|---|---|
| League Score | 86.9 | 75.4 | Claude Sonnet 5.5 |
| Coding (SWE-bench %) | — | — | — |
| Reasoning (GPQA %) | — | 90.9 | — |
| Context (tokens) | 1000000 | 1000000 | Draw |
| Speed (tok/s) | — | 213 | — |
| Price (blended $/1M) | $4.00 | $0.52 | DeepSeek V4.1 Flash (cheaper) |
Tale of the tape
| Spec | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| Maker | Anthropic | DeepSeek |
| Released | Sep 28, 2026 | Sep 10, 2026 |
| League Score | 87 | 75 |
| Context | 1,000,000 tokens | 1,000,000 tokens |
| Max output | 128,000 | 384,000 |
| $/1M input | $2.00 | $0.30 |
| $/1M output | $10.00 | $1.20 |
| Weights | Closed | Open |
| Speed | — | 213 t/s |
Head-to-head benchmarks (shared only)
| Benchmark | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| LiveBench overall | 82.5 | 77.3 |
Cost at three workloads
| Workload | Claude Sonnet 5.5 | DeepSeek V4.1 Flash |
|---|---|---|
| Light — 1M in / 250K out | $4.50 | $0.60 |
| Standard — 10M in / 2.5M out | $45.00 | $6.00 |
| Long-context — 50M in / 5M out | $150.00 | $21.00 |
The pick
Pick Claude Sonnet 5.5 if you want the higher overall League Score.
Pick DeepSeek V4.1 Flash if you want the lower running cost; you want downloadable weights / self-hosting.
All figures from the model database — sources and dates on each model page. Cost your own workload or compare a different pair.
Frequently asked questions
Which is better overall, Claude Sonnet 5.5 or DeepSeek V4.1 Flash?
Claude Sonnet 5.5 leads on overall League Score, 87 to 75 — a gap of 12 points on a composite of sourced benchmarks. That is overall form, not every category: check the per-category verdicts before choosing.
Which is cheaper, Claude Sonnet 5.5 or DeepSeek V4.1 Flash?
DeepSeek V4.1 Flash is cheaper: $0.52 vs $4.00 blended per 1M tokens (3:1 input/output mix) — about 7.6x less per token.
Which has the bigger context window, Claude Sonnet 5.5 or DeepSeek V4.1 Flash?
Neither — both take 1M of context.
Are Claude Sonnet 5.5 and DeepSeek V4.1 Flash open source?
Claude Sonnet 5.5 is closed weights — API access only; DeepSeek V4.1 Flash is open weights — it can be downloaded and self-hosted.