Noometry

Model comparison

Claude Opus 5.5 vs Mistral Small 3.1

Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 31.7 on the Noometry Index. Mistral Small 3.1 costs 20× less per token, which makes it the better buy when Claude Opus 5.5's lead doesn't matter for your workload.

Last verified . 19 shared benchmarks.

Claude Opus 5.5 Anthropic

68.6

Rank #3 Confirmed

Mistral Small 3.1 Mistral AI

31.7

Rank #269 Confirmed

Summary

  • They share 19 benchmarks with published results for both. Claude Opus 5.5 scores higher in 9 categories and Mistral Small 3.1 in 0 categories; 9 gaps are clear of the uncertainty.
  • The widest gap is in math, where Claude Opus 5.5 leads 91.8 to 14.7.
  • The biggest single-benchmark swing is OTIS Mock AIME 2024-2025: 100% for Claude Opus 5.5 and 3.9% for Mistral Small 3.1.
  • Mistral Small 3.1 is cheaper at $0.35 / $0.56 per million input/output tokens, against $4 / $20 for Claude Opus 5.5.
  • Claude Opus 5.5 accepts more context: 1M tokens versus 128K.
  • Mistral Small 3.1 has downloadable open weights; the other is API-only.

Side by side

Claude Opus 5.5Mistral Small 3.1
ProviderAnthropicMistral AI
Noometry Index68.631.7
Released2026-09-222025-03-17
WeightsProprietaryOpen
Context window1M128K
Max output128K102K
Input $ / M tokens$4$0.35
Output $ / M tokens$20$0.56
Results tracked4428

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Category by category

Coding Claude Opus 5.5 leads

Claude Opus 5.5: 71.9 (#3), Mistral Small 3.1: 38.3 (#179)

BenchmarkClaude Opus 5.5Mistral Small 3.1
LMArena Coding15471309
FrontierCode54.6%—
CursorBench57.8%—
LMArena WebDev1813—
FrontierSWE62.3%—
SciCode66.9%—
MirrorCode77.4%—
ALE-Bench2,147—

Agentic & Tool Use Not comparable

Claude Opus 5.5: 45.3 (#15), Mistral Small 3.1: —

BenchmarkClaude Opus 5.5Mistral Small 3.1
APEX-Agents73.5%—
GDP.pdf30.6%—
Vending-Bench 29,235—

Reasoning Claude Opus 5.5 leads

Claude Opus 5.5: 80.2 (#3), Mistral Small 3.1: 19.7 (#254)

BenchmarkClaude Opus 5.5Mistral Small 3.1
LMArena Hard Prompts15351278
Epoch Capabilities Index167.33127.48
ARC-AGI-293.3%—
NYT Connections (extended)88.5%—
ARC-AGI-198.5%—
CritPt31.7%—
Chess Puzzles—1%
EBR-Bench71.4%—
Mystery Game Puzzles71%—
DTBench98.9%—
LMCA68.2%—

Math Claude Opus 5.5 leads

Claude Opus 5.5: 91.8 (#3), Mistral Small 3.1: 14.7 (#301)

BenchmarkClaude Opus 5.5Mistral Small 3.1
OTIS Mock AIME 2024-2025100%3.9%
LMArena Math15061262
FrontierMath (Tiers 1-3)91.2%—
FrontierMath Tier 495%—
ProofBench100%—
Omni-MATH—24.8%
FrontierMath Erdős2.9%—

Knowledge Claude Opus 5.5 leads

Claude Opus 5.5: 66.4 (#10), Mistral Small 3.1: 22.6 (#271)

BenchmarkClaude Opus 5.5Mistral Small 3.1
GPQA Diamond90.6%41.9%
LMArena Expert15471257
SimpleQA Verified72.2%—
MMLU-Pro—61%
GPQA (HELM)—39.2%

Multimodal Claude Opus 5.5 leads

Claude Opus 5.5: 57.8 (#1), Mistral Small 3.1: 33.2 (#99)

BenchmarkClaude Opus 5.5Mistral Small 3.1
LMArena Vision13211136
Blueprint-Bench 251.2%—
Furniture Assembly83.3%—

Multilingual Claude Opus 5.5 leads

Claude Opus 5.5: 59.1 (#2), Mistral Small 3.1: 41.2 (#209)

BenchmarkClaude Opus 5.5Mistral Small 3.1
LMArena Non-English15071255
LMArena Chinese15881253
LMArena French15141273
LMArena Russian15201263
LMArena Spanish15071283
LMArena German—1266
LMArena Japanese—1208
LMArena Korean—1206

Instruction Following Claude Opus 5.5 leads

Claude Opus 5.5: 80.0 (#3), Mistral Small 3.1: 63.6 (#230)

BenchmarkClaude Opus 5.5Mistral Small 3.1
LMArena Instruction Following15371264
IFEval—75%

Long Context Claude Opus 5.5 leads

Claude Opus 5.5: 47.1 (#19), Mistral Small 3.1: 39.5 (#178)

BenchmarkClaude Opus 5.5Mistral Small 3.1
LMArena Longer Query15321299

Writing & Preference Claude Opus 5.5 leads

Claude Opus 5.5: 78.2 (#3), Mistral Small 3.1: 37.0 (#259)

BenchmarkClaude Opus 5.5Mistral Small 3.1
LMArena Text15151277
LMArena Creative Writing15331253
EQ-Bench Creative Writing2050761
LMArena Multi-Turn14991270
WildBench—78.8%

Frequently asked questions

Is Claude Opus 5.5 better than Mistral Small 3.1?

Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 31.7 on the Noometry Index. Mistral Small 3.1 costs 20× less per token, which makes it the better buy when Claude Opus 5.5's lead doesn't matter for your workload.

Which is cheaper, Claude Opus 5.5 or Mistral Small 3.1?

Mistral Small 3.1 is cheaper. It lists at $0.35 per million input tokens and $0.56 per million output tokens; Claude Opus 5.5 lists at $4 and $20.

Is Claude Opus 5.5 or Mistral Small 3.1 better for coding?

Claude Opus 5.5 scores higher on coding benchmarks: 71.9 versus 38.3 in the Noometry coding category.

Which has the bigger context window?

Claude Opus 5.5 does, with 1M tokens against 128K.

How many benchmarks do Claude Opus 5.5 and Mistral Small 3.1 share?

19 benchmarks have published results for both models. Claude Opus 5.5 has 44 scored results on Noometry and Mistral Small 3.1 has 28.

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