Claude Sonnet 4.5 vs StepFun Step-2
Claude Sonnet 4.5 (2025) and StepFun Step-2 (2025) are frontier reasoning models from Anthropic and StepFun. Claude Sonnet 4.5 ships a 200K-token context window, while StepFun Step-2 ships a 128k-token context window. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing. The goal is to make the tradeoff clear before deeper testing.
StepFun Step-2 is safer overall; choose Claude Sonnet 4.5 when reasoning depth matters.
Specs
| Released | 2025-09-29 | 2025-10-15 |
| Context window | 200K | 128k |
| Parameters | — | — |
| Architecture | decoder only | - |
| License | Proprietary | Proprietary |
| Knowledge cutoff | 2025-12 | - |
Pricing and availability
| Claude Sonnet 4.5 | StepFun Step-2 | |
|---|---|---|
| Input price | $3/1M tokens | - |
| Output price | $15/1M tokens | - |
| Providers | - |
Capabilities
| Claude Sonnet 4.5 | StepFun Step-2 | |
|---|---|---|
| Vision | ||
| Multimodal | ||
| Reasoning | ||
| Function calling | ||
| Tool use | ||
| Structured outputs | ||
| Code execution |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: Claude Sonnet 4.5, multimodal input: Claude Sonnet 4.5, reasoning mode: Claude Sonnet 4.5, function calling: Claude Sonnet 4.5, tool use: Claude Sonnet 4.5, and structured outputs: Claude Sonnet 4.5. Both models share the core language-model surface, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
Pricing coverage is uneven: Claude Sonnet 4.5 has $3/1M input tokens and StepFun Step-2 has no token price sourced yet. Provider availability is 8 tracked routes versus 0. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Claude Sonnet 4.5 when reasoning depth, larger context windows, and broader provider choice are central to the workload. Choose StepFun Step-2 when provider fit are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions.
FAQ
Which has a larger context window, Claude Sonnet 4.5 or StepFun Step-2?
Claude Sonnet 4.5 supports 200K tokens, while StepFun Step-2 supports 128k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Is Claude Sonnet 4.5 or StepFun Step-2 open source?
Claude Sonnet 4.5 is listed under Proprietary. StepFun Step-2 is listed under Proprietary. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, Claude Sonnet 4.5 or StepFun Step-2?
Claude Sonnet 4.5 has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for multimodal input, Claude Sonnet 4.5 or StepFun Step-2?
Claude Sonnet 4.5 has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for reasoning mode, Claude Sonnet 4.5 or StepFun Step-2?
Claude Sonnet 4.5 has the clearer documented reasoning mode signal in this comparison. If reasoning mode is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run Claude Sonnet 4.5 and StepFun Step-2?
Claude Sonnet 4.5 is available on Microsoft Foundry, Anthropic, Snowflake Cortex, GCP Vertex AI, and AWS Bedrock. StepFun Step-2 is available on the tracked providers still being sourced. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-04-24. Data sourced from public model cards and provider documentation.