Model comparison
Claude Sonnet 5.5 vs Step 3.7 Flash
Claude Sonnet 5.5 is the stronger model overall, scoring 60.5 to 36.5 on the Noometry Index. Step 3.7 Flash costs 9.6× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Last verified . 3 shared benchmarks.
StepFunSummary
- They share 3 benchmarks with published results for both. Claude Sonnet 5.5 scores higher in 3 categories and Step 3.7 Flash in 0 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Sonnet 5.5 leads 88.7 to 40.9.
- The biggest single-benchmark swing is CritPt: 31.4% for Claude Sonnet 5.5 and 2.3% for Step 3.7 Flash.
- Step 3.7 Flash is cheaper at $0.18 / $1.11 per million input/output tokens, against $2 / $10 for Claude Sonnet 5.5.
- Claude Sonnet 5.5 accepts more context: 1M tokens versus 256K.
- Step 3.7 Flash has downloadable open weights; the other is API-only.
Side by side
| Claude Sonnet 5.5 | Step 3.7 Flash | |
|---|---|---|
| Provider | Anthropic | StepFun |
| Noometry Index | 60.5 | 36.5 |
| Released | 2026-09-28 | 2026-05-29 |
| Weights | Proprietary | Open |
| Context window | 1M | 256K |
| Max output | 128K | 256K |
| Input $ / M tokens | $2 | $0.18 |
| Output $ / M tokens | $10 | $1.11 |
| Results tracked | 16 | 5 |
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Category by category
Coding Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 65.5 (#6), Step 3.7 Flash: 39.4 (#147)
| Benchmark | Claude Sonnet 5.5 | Step 3.7 Flash |
|---|---|---|
| SciCode | 61% | 40% |
| ALE-Bench | 1,819 | 694.12 |
| FrontierCode | 52.1% | — |
| CursorBench | 55.5% | — |
| LMArena WebDev | 1699 | — |
| FrontierSWE | 61.9% | — |
Agentic & Tool Use Not comparable
Claude Sonnet 5.5: 44.9 (#14), Step 3.7 Flash: —
| Benchmark | Claude Sonnet 5.5 | Step 3.7 Flash |
|---|---|---|
| APEX-Agents | 75.5% | — |
Reasoning Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 52.4 (#29), Step 3.7 Flash: 20.9 (#211)
| Benchmark | Claude Sonnet 5.5 | Step 3.7 Flash |
|---|---|---|
| CritPt | 31.4% | 2.3% |
| NYT Connections (extended) | — | 39.7% |
| Mystery Game Puzzles | 65% | — |
Math Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 88.7 (#4), Step 3.7 Flash: 40.9 (#74)
| Benchmark | Claude Sonnet 5.5 | Step 3.7 Flash |
|---|---|---|
| FrontierMath (Tiers 1-3) | 88.8% | — |
| FrontierMath Tier 4 | 80.5% | — |
| MathArena Final-Answer Competitions | — | 68.5% |
| OTIS Mock AIME 2024-2025 | 100% | — |
| ProofBench | 100% | — |
Knowledge Not comparable
Claude Sonnet 5.5: 66.0 (#11), Step 3.7 Flash: —
| Benchmark | Claude Sonnet 5.5 | Step 3.7 Flash |
|---|---|---|
| GPQA Diamond | 95.6% | — |
| SimpleQA Verified | 46.5% | — |
Multimodal Not comparable
Claude Sonnet 5.5: 53.2 (#5), Step 3.7 Flash: —
| Benchmark | Claude Sonnet 5.5 | Step 3.7 Flash |
|---|---|---|
| Furniture Assembly | 75% | — |
Frequently asked questions
Is Claude Sonnet 5.5 better than Step 3.7 Flash?
Claude Sonnet 5.5 is the stronger model overall, scoring 60.5 to 36.5 on the Noometry Index. Step 3.7 Flash costs 9.6× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Which is cheaper, Claude Sonnet 5.5 or Step 3.7 Flash?
Step 3.7 Flash is cheaper. It lists at $0.18 per million input tokens and $1.11 per million output tokens; Claude Sonnet 5.5 lists at $2 and $10.
Is Claude Sonnet 5.5 or Step 3.7 Flash better for coding?
Claude Sonnet 5.5 scores higher on coding benchmarks: 65.5 versus 39.4 in the Noometry coding category.
Which has the bigger context window?
Claude Sonnet 5.5 does, with 1M tokens against 256K.
How many benchmarks do Claude Sonnet 5.5 and Step 3.7 Flash share?
3 benchmarks have published results for both models. Claude Sonnet 5.5 has 16 scored results on Noometry and Step 3.7 Flash has 5.