Step 3.5 Flash vs StepFun Step-2
Step 3.5 Flash (2026) and StepFun Step-2 (2025) are frontier reasoning models from StepFun. Step 3.5 Flash ships a 256k-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.
Step 3.5 Flash is safer overall; choose StepFun Step-2 when provider fit matters.
Decision scorecard
Local evidence first| Signal | Step 3.5 Flash | StepFun Step-2 |
|---|---|---|
| Best for | reasoning-heavy apps | general production evaluation |
| Decision fit | Long context | Long context |
| Context window | 256k | 128k |
| Cheapest output | $0.30/1M tokens | - |
| Provider routes | 1 tracked | 0 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Step 3.5 Flash has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Step 3.5 Flash has broader tracked provider coverage for fallback and procurement flexibility.
- Step 3.5 Flash uniquely exposes Reasoning in local model data.
- Local decision data tags Step 3.5 Flash for Long context.
- Local decision data tags StepFun Step-2 for Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Step 3.5 Flash
$155
Cheapest tracked route/tier: OpenRouter
StepFun Step-2
Unavailable
No complete token price in local provider data
Cost delta unavailable until both models have sourced input and output token prices.
Switch friction
- No overlapping tracked provider route is sourced for Step 3.5 Flash and StepFun Step-2; plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Reasoning before moving production traffic.
- No overlapping tracked provider route is sourced for StepFun Step-2 and Step 3.5 Flash; plan for SDK, billing, or endpoint changes.
- Step 3.5 Flash adds Reasoning in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-01-29 | 2025-10-15 |
| Context window | 256k | 128k |
| Parameters | 196B (11B active) | 1T (MoE)* |
| Architecture | mixture of experts | - |
| License | Open Source | Proprietary |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Step 3.5 Flash | StepFun Step-2 |
|---|---|---|
| Input price | $0.10/1M tokens | - |
| Output price | $0.30/1M tokens | - |
| Providers | - |
Capabilities
| Capability | Step 3.5 Flash | StepFun Step-2 |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | Yes | No |
| Function calling | No | No |
| Tool use | No | No |
| Structured outputs | No | No |
| Code execution | No | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on reasoning mode: Step 3.5 Flash. 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: Step 3.5 Flash has $0.10/1M input tokens and StepFun Step-2 has no token price sourced yet. Provider availability is 1 tracked routes versus 0. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Step 3.5 Flash 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. It also helps separate model capability from provider packaging, which can change cost and latency. For teams standardizing a stack, that distinction is often the difference between a benchmark win and a reliable deployment.
FAQ
Which has a larger context window, Step 3.5 Flash or StepFun Step-2?
Step 3.5 Flash supports 256k 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 Step 3.5 Flash or StepFun Step-2 open source?
Step 3.5 Flash is listed under Open Source. 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 reasoning mode, Step 3.5 Flash or StepFun Step-2?
Step 3.5 Flash 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 Step 3.5 Flash and StepFun Step-2?
Step 3.5 Flash is available on OpenRouter. StepFun Step-2 is available on the tracked providers still being sourced. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
When should I pick Step 3.5 Flash over StepFun Step-2?
Step 3.5 Flash is safer overall; choose StepFun Step-2 when provider fit matters. If your workload also depends on reasoning depth, start with Step 3.5 Flash; if it depends on provider fit, run the same evaluation with StepFun Step-2.
Continue comparing
Last reviewed: 2026-05-29. Data sourced from public model cards and provider documentation.