stepfun

StepFun 3.5 Flash

Step 3.5 Flash is an open-source reasoning model by StepFun with 196B total parameters (11B active) using Mixture of Experts. It features a 256K context window, deep reasoning, tool calling, and agentic capabilities, achieving 97.3 on AIME 2025 and 74.4% on SWE-bench Verified.

text inputimage inputtext outputlanguage

Use with MiniRouter View docs

1const response = await fetch('https://api.minirouter.sh/v1/chat/completions', {2  method: 'POST',3  headers: {4    Authorization: `Bearer ${process.env.MINIROUTER_KEY}`,5    'Content-Type': 'application/json',6  },7  body: JSON.stringify({8    model: 'stepfun/step-3.5-flash',9    messages: [{ role: 'user', content: 'Why is the sky blue?' }],10  }),11})12 13const data = await response.json()14console.log(data.choices[0].message.content)

Read docs →

Overview

Model type: language
Context window: 262,114
Maximum output: 262,114
Input / 1M tokens: $0.0945
Output / 1M tokens: $0.315
Released: 2026-01-29

Prices include the MiniRouter fee. Compatibility snapshot: 2026-08-06. Input: text, image. Output: text.

Endpoints

/v1/chat/completions/v1/messages/v1/responses

Platform-funded routing only. Caller BYOK credentials and OIDC-based upstream authentication are intentionally excluded; authenticate with a MiniRouter bearer key.

Captured parameters: max_tokens, temperature, stop, tools, tool_choice, reasoning, include_reasoning.

API

Use the setup panel above to switch between Chat Completions, Messages, and client configurations. Every snippet keeps the model ID unchanged.

Base URLhttps://api.minirouter.sh/v1

Model IDstepfun/step-3.5-flash

Providers

MiniRouter selects from the configured routes below. Priority is the catalog order, not a latency or availability score.

Provider	Priority	Input / 1M	Output / 1M	Parameters	Access
vercel	1	$0.0945	$0.315	max_tokens, temperature, stop, tools, tool_choice, reasoning, include_reasoning	MiniRouter balance