Noometry

Model comparison

Claude Sonnet 4.5 vs Step 3.5 Flash

Claude Sonnet 4.5 is the stronger model overall, scoring 44.1 to 42.3 on the Noometry Index. Step 3.5 Flash costs 40× less per token, which makes it the better buy when Claude Sonnet 4.5's lead doesn't matter for your workload.

Last verified . 18 shared benchmarks.

Claude Sonnet 4.5 Anthropic

44.1

Rank #81 Confirmed

Step 3.5 Flash StepFun

42.3

Rank #116 Confirmed

Summary

  • They share 18 benchmarks with published results for both. Claude Sonnet 4.5 scores higher in 7 categories and Step 3.5 Flash in 1 category; 8 gaps are clear of the uncertainty.
  • The widest gap is in math, where Step 3.5 Flash leads 42.6 to 32.3.
  • The biggest single-benchmark swing is NYT Connections (extended): 37.3% for Claude Sonnet 4.5 and 28.4% for Step 3.5 Flash.
  • Step 3.5 Flash is cheaper at $0.10 / $0.30 per million input/output tokens, against $3 / $15 for Claude Sonnet 4.5.
  • Step 3.5 Flash accepts more context: 256K tokens versus 200K.
  • Step 3.5 Flash has downloadable open weights; the other is API-only.

Side by side

Claude Sonnet 4.5Step 3.5 Flash
ProviderAnthropicStepFun
Noometry Index44.142.3
Released2025-09-292026-01-29
WeightsProprietaryOpen
Context window200K256K
Max output64K256K
Input $ / M tokens$3$0.10
Output $ / M tokens$15$0.30
Results tracked7319

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Category by category

Coding Claude Sonnet 4.5 leads

Claude Sonnet 4.5: 47.3 (#61), Step 3.5 Flash: 42.4 (#105)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
LMArena Coding14891436
SWE-bench Verified71.3%—
SWE-bench Verified (bash only)71.4%—
LMArena WebDev1393—
SWE-bench Multilingual67%—
SciCode44.7%—
GSO14.7%—
WeirdML47.7%—
ALE-Bench796.15—
AlgoTune1.52—

Agentic & Tool Use Not comparable

Claude Sonnet 4.5: 38.3 (#32), Step 3.5 Flash: —

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
Terminal-Bench46.5%—
Berkeley Function Calling Leaderboard73.2%—
GDPval42.5%—
Remote Labor Index2.1%—
τ²-bench Airline72%—
τ²-bench Banking25.3%—
τ²-bench Retail72.4%—
τ²-bench Telecom84.9%—
Cybench60%—
DeepResearch Bench52.6%—
OSWorld62.9%—
LMArena Search1159—
METR Time Horizons67.4%—
Vending-Bench 23,839—

Reasoning Claude Sonnet 4.5 leads

Claude Sonnet 4.5: 26.9 (#125), Step 3.5 Flash: 22.2 (#202)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
NYT Connections (extended)37.3%28.4%
LMArena Hard Prompts14621411
ARC-AGI-213.6%—
SimpleBench54.3%—
Kagi LLM Benchmark57.9%—
ARC-AGI-163.7%—
CritPt1.1%—
Chess Puzzles12%—
EnigmaEval6%—
EBR-Bench2.4%—
Mystery Game Puzzles17%—
DTBench83.2%—
LMCA38.8%—
Epoch Capabilities Index146.84—
ForecastBench61.9—

Math Step 3.5 Flash leads

Claude Sonnet 4.5: 32.3 (#216), Step 3.5 Flash: 42.6 (#84)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
LMArena Math14491408
FrontierMath (Tiers 1-3)23.9%—
FrontierMath Tier 42.4%—
MathArena Final-Answer Competitions—66.8%
OTIS Mock AIME 2024-202577.8%—
ProofBench19%—
Omni-MATH55.3%—
MATH Level 597.7%—
FrontierMath (Feb 2025 set)15.2%—
FrontierMath Tier 4 (v1)4.2%—

Knowledge Claude Sonnet 4.5 leads

Claude Sonnet 4.5: 48.4 (#76), Step 3.5 Flash: 39.6 (#132)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
LMArena Expert14821421
GPQA Diamond82.3%—
Humanity's Last Exam13.7%—
SimpleQA Verified30.7%—
MMLU-Pro86.9%—
Vectara Hallucination Rate12%—
GPQA (HELM)68.6%—

Multimodal Not comparable

Claude Sonnet 4.5: 34.8 (#89), Step 3.5 Flash: —

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
VPCT39.8%—
LMArena Document1450—

Multilingual Claude Sonnet 4.5 leads

Claude Sonnet 4.5: 53.4 (#69), Step 3.5 Flash: 50.5 (#119)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
LMArena Non-English14251385
LMArena Chinese14591447
LMArena French14581421
LMArena German14271405
LMArena Japanese13901354
LMArena Korean14031352
LMArena Russian14371385
LMArena Spanish14571419

Instruction Following Claude Sonnet 4.5 leads

Claude Sonnet 4.5: 75.0 (#78), Step 3.5 Flash: 73.1 (#124)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
LMArena Instruction Following14591385
IFEval85%—

Long Context Claude Sonnet 4.5 leads

Claude Sonnet 4.5: 45.2 (#46), Step 3.5 Flash: 42.8 (#117)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
LMArena Longer Query14761402

Writing & Preference Claude Sonnet 4.5 leads

Claude Sonnet 4.5: 66.5 (#34), Step 3.5 Flash: 58.8 (#113)

BenchmarkClaude Sonnet 4.5Step 3.5 Flash
LMArena Text14391403
LMArena Creative Writing14421357
LMArena Multi-Turn14651405
EQ-Bench Creative Writing1678—
WildBench85.4%—

Frequently asked questions

Is Claude Sonnet 4.5 better than Step 3.5 Flash?

Claude Sonnet 4.5 is the stronger model overall, scoring 44.1 to 42.3 on the Noometry Index. Step 3.5 Flash costs 40× less per token, which makes it the better buy when Claude Sonnet 4.5's lead doesn't matter for your workload.

Which is cheaper, Claude Sonnet 4.5 or Step 3.5 Flash?

Step 3.5 Flash is cheaper. It lists at $0.10 per million input tokens and $0.30 per million output tokens; Claude Sonnet 4.5 lists at $3 and $15.

Is Claude Sonnet 4.5 or Step 3.5 Flash better for coding?

Claude Sonnet 4.5 scores higher on coding benchmarks: 47.3 versus 42.4 in the Noometry coding category.

Which has the bigger context window?

Step 3.5 Flash does, with 256K tokens against 200K.

How many benchmarks do Claude Sonnet 4.5 and Step 3.5 Flash share?

18 benchmarks have published results for both models. Claude Sonnet 4.5 has 73 scored results on Noometry and Step 3.5 Flash has 19.

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