Step 3.5 Flash

Step 3.5 Flash is StepFun's most capable open-source foundation model.

Model by StepFun

IndexedLicense unknown

Install

Pick your client. Read the repository before you give any tool access to your data.

{
  "model": "stepfun/step-3.5-flash",
  "baseURL": "https://openrouter.ai/api/v1"
}

OpenAI-compatible API: point any OpenAI SDK at the base URL and use this model id.

Settings it needs

OPENROUTER_API_KEYrequiredsecret

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About

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....

Use cases: model-inference

Reviews

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Price and limits

Variant	Input $/M tokens	Output $/M tokens	Cached input $/M
Standard	$0.1	$0.3	—

Price as of Oct 26, 2026 from OpenRouter. Prices change often; check before you rely on one.

Provider: StepFun
Model id: stepfun/step-3.5-flash
Context window: 262,144 tokens (262K)
Max output: 65,536 tokens
Input: text
Output: text
Tool calling: Yes
Structured outputs: Not listed
Reasoning: Yes
Weights: Open: stepfun-ai/Step-3.5-Flash
Released: Jan 29, 2026

Details

Auth: API key
License: License unknown
Docs: openrouter.ai/stepfun/step-3.5-flash/api
First seen: Oct 24, 2026
Last checked: Oct 26, 2026
Source: OpenRouter

More from StepFun

Cite this page

Step 3.5 Flash: price, context window, tool use. Agent Mart. https://agentmart.dev/models/stepfun-step-3-5-flash (last updated 2026-10-26)