Step 3.5 Flash
Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token. It is a reasoning model that is incredibly speed efficient even at long contexts.
- Organization
- StepFun (China)
- Family
- step
- Providers
- 15
- Context
- 256,000
- Output limit
- 256,000
- Knowledge
- 2025-01
- Release
- 2026-01-29
- Updated
- 2026-02-13
- Weights
- Open
- Input
- text
- Output
- text
- Capabilities
- —
Providers
Compare every cataloged offer for this model, including its provider, route, token limits, price, and capabilities.
| Provider | Model ID | Context | Output | Input / output · 1M | Reasoning | Tools | Structured | Details |
|---|---|---|---|---|---|---|---|---|
| CommandCode | stepfun/Step-3.5-Flash | 256,000 | 256,000 | — / — | — | — | — | View |
| Eden AI | deepinfra/stepfun-ai/Step-3.5-Flash | 262,144 | 256,000 | — / — | — | — | — | View |
| EmpirioLabs AI | step-3-5-flash | 256,000 | 131,072 | — / — | — | — | — | View |
| Hugging Face | stepfun-ai/Step-3.5-Flash | 262,144 | 256,000 | — / — | — | — | — | View |
| Kilo Gateway | stepfun/step-3.5-flash | 262,144 | 65,536 | — / — | — | — | — | View |
| NanoGPT | stepfun-ai/step-3.5-flash | 262,144 | 65,536 | — / — | — | — | — | View |
| SiliconFlowvia OpenRouter | stepfun/step-3.5-flash fp8 | 262,144 | 65,536 | $0.10 / $0.30 | Yes | Yes | No | View |
| Qiniu | stepfun/step-3.5-flash | 64,000 | 4,096 | — / — | — | — | — | View |
| SiliconFlow | stepfun-ai/Step-3.5-Flash | 262,000 | 66,000 | — / — | — | — | — | View |
| SiliconFlow (China) | stepfun-ai/Step-3.5-Flash | 262,000 | 262,000 | — / — | — | — | — | View |
| StepFun (China) | step-3.5-flash | 256,000 | 256,000 | — / — | — | — | — | View |
| StepFun (Global) | step-3.5-flash | 256,000 | 256,000 | — / — | — | — | — | View |
| StepFun Step Plan (China) | step-3.5-flash | 256,000 | 256,000 | — / — | — | — | — | View |
| StepFun Step Plan (Global) | step-3.5-flash | 256,000 | 256,000 | — / — | — | — | — | View |
| ZenMux | stepfun/step-3.5-flash | 256,000 | 256,000 | — / — | — | — | — | View |
Prices and limits apply to each offer. A dash means the value is not provided. OpenRouter offers show the hosting provider and routing channel separately.
Pricing
Compare token rates and cache charges across available routes and hosting configurations.
Lowest listed input and output prices across the offers above; they may belong to different providers. These are base rates, before conditional pricing, discounts or additional fees.
stepfun/step-3.5-flashObserved - Input
- $0.10
- Output
- $0.30
Hosting prices through OpenRouter All endpoints and cache rates
| Endpoint | Input / 1M | Output / 1M | Cache read / 1M | Cache write / 1M |
|---|---|---|---|---|
| SiliconFlowsiliconflow/fp8 | $0.10 | $0.30 | — | — |
Each row is a hosting configuration. Open an offer in Providers for its full pricing conditions and additional fees. Endpoint observations may differ from the routing catalog's base price.
Performance
Review reported latency and output-throughput percentiles from the latest observed rolling window.
Time to first token · milliseconds
All latency percentiles 1 endpoints
| Endpoint | P50 | P75 | P90 | P99 |
|---|---|---|---|---|
| SiliconFlowsiliconflow/fp8 | 877 ms | 1,271.5 ms | 1,922 ms | 3,017.6 ms |
Output throughput · tokens per second
All throughput percentiles 1 endpoints
| Endpoint | P50 | P75 | P90 | P99 |
|---|---|---|---|---|
| SiliconFlowsiliconflow/fp8 | 63 t/s | 70 t/s | 76.8 t/s | 89.88 t/s |
Percentiles describe the observed request distribution. These are snapshots of a rolling window, not a historical time series.
Uptime
Compare successful request rates across the latest 5-minute, 30-minute, and 24-hour observations.
Reported by OpenRouter at the time of collection; rate-limited requests are excluded. A dash means no measurement was reported. This is not a live availability check.
Benchmarks
Review attributed evaluation results on each source's original scale.
stepfun/step-3.5-flashObserved Sources: Artificial Analysis and Design Arena, via OpenRouter. Scores retain their original scales and are not OpenAI Suite ratings.
Detailed evaluations
| Evaluation | Configuration | Source | Results | Details |
|---|---|---|---|---|
| Composite indices | Step 3.5 Flash 2603stepfun/step-3.5-flash | Artificial Analysis | Intelligence 17 · Coding — · Agentic — | Details |
Sources: Artificial Analysis, Design Arena and OpenRouter. Evaluation configurations and scales differ; results are not interchangeable. Updated Oct 24, 2026.
Technical details & API
Explore specifications, supported parameters, reasoning controls, and API identifiers for each OpenRouter route.
stepfun/step-3.5-flashObserved - Context
- 262,144
- Maximum output
- 65,536
- Tokenizer
- Other
- Input
- text
- Output
- text
- Moderation
- No
- Added to OpenRouter
- 2026-01-29
https://openrouter.ai/api/v1stepfun/step-3.5-flashstepfun/step-3.5-flashstepfun-ai/Step-3.5-FlashReasoning
- Required
- Yes
- Enabled by default
- Not reported
- Default effort
- —
- Supported efforts
- —
Supported parameters
frequency_penaltyinclude_reasoningmax_tokensreasoningtemperaturetool_choicetoolstop_ktop_p
Frequently asked questions
Answers based on the model metadata and serving offers currently in the catalog.
How much does Step 3.5 Flash cost?
Listed rates start at $0.10 per million input tokens and $0.30 per million output tokens. Prices vary by provider and configuration; see Pricing for details.
Which providers offer Step 3.5 Flash?
There are 15 cataloged offers across 15 providers. Compare model IDs, prices and limits in Providers.
What is the context window?
The cataloged model context is 256,000 tokens. Each serving endpoint may apply a different limit.
Does it support tools and structured output?
Tool calling: Not reported. Structured output: Not reported. Support can vary by endpoint.
Resources
Catalog history · 4 recorded revisions
Metadata observations since this model was first cataloged. These are not model release versions.
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