Discover StepFun's Step 3.5 Flash Model

Step 3.5 Flash excels in reasoning and speed efficiency.

Input: text Output: text Context: 256,000 tokens Release: 2026-01-29

StepFun's Step 3.5 Flash, released on January 29, 2026, is a cutting-edge open-source foundation model designed for efficient reasoning. Utilizing a sparse Mixture of Experts (MoE) architecture, it activates only 11 billion of its 196 billion parameters per token, ensuring speed and efficiency even with long contexts. This model supports text-to-text input and output modalities, making it versatile for various applications. With a context length of 256,000 tokens, it can handle extensive data while providing insightful responses. Whether you're looking to enhance your text generation tasks or improve reasoning capabilities, Step 3.5 Flash offers a robust solution.

Use Cases

Here are a few ways teams apply StepFun: Step 3.5 Flash (free) in practice—from fast drafting to multimodal understanding. Adapt these ideas to your workflow.

Generate insightful text responses

Enhance reasoning in applications

Handle extensive data with ease

Improve text generation tasks

Key Features

A quick look at the capabilities that make this model useful in real projects.

Sparse Mixture of Experts architecture

Activates 11B of 196B parameters per token

Supports 256,000 token context length

Text-to-text input and output modalities

Open-source and free to use

Specs

Overview

Vendor
stepfun

Model ID
stepfun/step-3.5-flash:free

Release
2026-01-29

Modalities & context

Input
text

Output
text

Context
256,000 tokens

Parameters & defaults

Supported parameters: frequency_penalty, include_reasoning, max_tokens, reasoning, stop, temperature, tools, top_p

Defaults: temperature 0.2, top_p 0.95

Benchmark tests: StepFun: Step 3.5 Flash (free)

We ran this model against a few representative prompts to show its range. Review the outputs below and be the judge.

Text

Prompt:

Write 150 words on how AI might positively upend work, leisure and creativity

AI promises not to replace us, but to radically augment human potential, upending traditional boundaries for the better. In **work**, it will automate mundane tasks, freeing us for strategic thinking, empathy, and complex problem-solving. New roles in AI oversight, ethics, and human-machine collaboration will emerge, shifting value from routine labor to creativity and judgment. For **leisure**, hyper-personalization will redefine entertainment and wellness. AI curators will design bespoke travel, learning, and media experiences, while intelligent companions could enrich social connection and mental health, making downtime more restorative and engaging. Most profoundly, **creativity** will be democratized and amplified. AI tools will act as collaborative partners, helping anyone prototype ideas, compose music, or draft stories, lowering technical barriers. The focus will shift from execution to vision, emotion, and meaning—the uniquely human heart of art. Ultimately, AI’s positive upending lies in its power to elevate our inherent strengths, transforming how we work, play, and imagine.

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up.end

/ˌəpˈend/

verb

To “upend” means to completely disrupt, overturn, or drastically change the established order or structure of something. It implies a significant shift or alteration that can potentially have far-reaching consequences. When something is upended, it is turned upside down or transformed in a way that challenges conventional norms or expectations. The term often carries a sense of innovation, transformation, and sometimes even a hint of upheaval, indicating that the changes are not just minor adjustments but rather a fundamental reimagining of the status quo.

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