← ModelRumors.ai buyer's guide
HEAD TO HEAD · UPDATED NOV 6, 2026
Claude Sonnet 5.5 vs DeepSeek V4.1-Flash
Anthropic against DeepSeek, on sourced numbers only. Green marks the higher (or cheaper) value on each row; the text below only calls a lead when the gap is bigger than measurement noise.
| Claude Sonnet 5.5 | DeepSeek V4.1-Flash | |
|---|---|---|
| Arena Elo | 1477 source ↗ | 1476 source ↗ |
| GPQA Diamond | 95.6% source ↗ | 90.9% source ↗ |
| $ per 1M in / out | $2 / $10 source ↗ | $0.15 / $0.60 source ↗ |
| Blended $ per 1M (3:1) | $4.00 source ↗ | $0.26 source ↗ |
| Context window | 1M source ↗ | 1M source ↗ |
| Output speed | 155 tok/s source ↗ | 174 tok/s source ↗ |
| Released | Sep 28, 2026 source ↗ | Sep 10, 2026 source ↗ |
| Open weights | No source ↗ | Yes source ↗ |
| Reasoning effort tiers | low · medium · high · xhigh · max (default: high) | low · high · max (default: high) |
| API effort control | output_config={"effort": "low" | "medium" | "high" | "xhigh" | "max"} source ↗ | thinking={"type": "enabled" | "disabled"}, reasoning_effort="low" | "high" | "max" (medium and xhigh map to high) source ↗ |
| Additional benchmarks | SWE-bench Pro: 81.3% source ↗ AA Intelligence Index v5.0.1: 55 source ↗ | DeepSWE v1.1: 77.0% (Oct 17 update; 74.2% on Sep 10) source ↗ |
| Best for (workload) | Fast (155 tok/s, Artificial Analysis) and strong on science: 95.6% GPQA Diamond at max effort (Epoch AI), above Opus 5.5's 90.6%. source ↗ | Fastest output we track (174 tok/s, Artificial Analysis) and the lowest list price ($0.15 / $0.60 off-peak); MIT open weights. source ↗ |
Arena Elo from the arena.ai text leaderboard as of Oct 27, 2026 source ↗. Speed measured by Artificial Analysis and varies by provider.
Which one should I use?
For high-volume work where cost matters most, DeepSeek V4.1-Flash is about 15.2 times cheaper per token. For hard science and analysis questions, Claude Sonnet 5.5 scores higher on GPQA Diamond (95.6% vs 90.9%). If you need to self-host or fine-tune, only DeepSeek V4.1-Flash has open weights. On release timing, Anthropic is at day 30 of a typical ~15-day gap (PAST TYPICAL GAP), and DeepSeek is at day 20 of a typical ~32-day gap (MID-CYCLE).
Key differences from the sourced numbers
- DeepSeek V4.1-Flash is the cheaper option: $0.26 vs $4.00 per 1M tokens at a 3:1 input-to-output mix (about 15.2 times less).
- On the Arena text leaderboard they are close (1477 vs 1476): a gap under 20 points is within the leaderboard's margin of error.
- On GPQA Diamond, graduate-level science questions, Claude Sonnet 5.5 leads 95.6% to 90.9%.
- Claude Sonnet 5.5 pricing note: Same rate across the full 1M context window.
- DeepSeek V4.1-Flash pricing note: Off-peak price (cache hit $0.003 / 1M). Peak hours (01:00 to 04:00 and 06:00 to 10:00 UTC, weekdays): $0.30 / $1.20 (cache hit $0.006 / 1M).
Frequently asked questions
Is Claude Sonnet 5.5 or DeepSeek V4.1-Flash better?
DeepSeek V4.1-Flash is the cheaper option: $0.26 vs $4.00 per 1M tokens at a 3:1 input-to-output mix (about 15.2 times less). On the Arena text leaderboard they are close (1477 vs 1476): a gap under 20 points is within the leaderboard's margin of error. On GPQA Diamond, graduate-level science questions, Claude Sonnet 5.5 leads 95.6% to 90.9%. Claude Sonnet 5.5 pricing note: Same rate across the full 1M context window. DeepSeek V4.1-Flash pricing note: Off-peak price (cache hit $0.003 / 1M). Peak hours (01:00 to 04:00 and 06:00 to 10:00 UTC, weekdays): $0.30 / $1.20 (cache hit $0.006 / 1M).
Which one should I use: Claude Sonnet 5.5 or DeepSeek V4.1-Flash?
For high-volume work where cost matters most, DeepSeek V4.1-Flash is about 15.2 times cheaper per token. For hard science and analysis questions, Claude Sonnet 5.5 scores higher on GPQA Diamond (95.6% vs 90.9%). If you need to self-host or fine-tune, only DeepSeek V4.1-Flash has open weights. On release timing, Anthropic is at day 30 of a typical ~15-day gap (PAST TYPICAL GAP), and DeepSeek is at day 20 of a typical ~32-day gap (MID-CYCLE).
How much does Claude Sonnet 5.5 cost compared with DeepSeek V4.1-Flash?
Claude Sonnet 5.5 lists at $2 / $10 per 1M input/output tokens ($4.00/1M blended at 3:1). DeepSeek V4.1-Flash lists at $0.15 / $0.60 per 1M input/output tokens ($0.26/1M blended at 3:1).
Facts checked Nov 5, 2026 against official sources. Every number links to its source. Spotted an error? Email [email protected].