StepFun: Step 3.5 Flash API

Access StepFun: Step 3.5 Flash from StepFun using Puter.js AI API.

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Model Card

Step 3.5 Flash is StepFun's open-source reasoning model built on a sparse Mixture of Experts architecture with 196B total parameters but only 11B active per token. It's optimized for agentic tasks and coding with ultra-fast inference speeds up to 350 tokens per second and supports 256K context length.

Context Window N/A

tokens

Max Output 256K

tokens

Input Cost $0.1

per million tokens

Output Cost $0.3

per million tokens

Release Date Feb 1, 2026

 

API Usage Example

Add StepFun: Step 3.5 Flash to your app with just a few lines of code.
No API keys, no backend, no configuration required.

// npm install @heyputer/puter.js
import { puter } from '@heyputer/puter.js';

puter.ai.chat("Explain quantum computing in simple terms", {
    model: "stepfun/step-3.5-flash"
}).then(response => {
    document.body.innerHTML = response.message.content;
});

<html>
<body>
    <script src="https://js.puter.com/v2/"></script>
    <script>
        puter.ai.chat("Explain quantum computing in simple terms", {
            model: "stepfun/step-3.5-flash"
        }).then(response => {
            document.body.innerHTML = response.message.content;
        });
    </script>
</body>
</html>

View full documentation →

Frequently Asked Questions

What is this StepFun: Step 3.5 Flash API about?

The StepFun: Step 3.5 Flash API gives you access to StepFun's chat model through Puter.js. With just a few lines of JavaScript, you can integrate StepFun: Step 3.5 Flash into any web app or Node.js project — no API keys, no backend, and no configuration required.

Who created StepFun: Step 3.5 Flash?

StepFun: Step 3.5 Flash was created by StepFun and released on Feb 1, 2026.

What is the max output length of StepFun: Step 3.5 Flash?

StepFun: Step 3.5 Flash can generate up to 256K tokens in a single response.

How much does it cost?
The StepFun: Step 3.5 Flash API is available through the User-Pays Model. As a developer, you can add the StepFun: Step 3.5 Flash API to your app for free — your users pay for their own AI costs directly.
Price per 1M tokens
Input$0.1
Output$0.3
How do I access the StepFun: Step 3.5 Flash API?

You can access the StepFun: Step 3.5 Flash API with just a few lines of JavaScript — no API keys, no backend, and no configuration required. Include the Puter.js library in your project and start making calls right away. For more details, check out our documentation.

Does the StepFun: Step 3.5 Flash API work with React / Vue / Vanilla JS / Node / etc.?

Yes — the StepFun: Step 3.5 Flash API works with any JavaScript framework, Node.js, or plain HTML through Puter.js. Just include the library and start building. See the documentation for more details.

Get started with Puter.js

Add StepFun: Step 3.5 Flash to your app without worrying about API keys or setup.

Read the Docs View Tutorials