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StepFun AIFebruary 1, 2026

Step 3.5 Flash

Open Source
LLM
LLMs
Open Source

Explore Step 3.5 Flash

Visit the official website to learn more and get started

### TL;DR

Step 3.5 Flash is an open-source foundation model engineered for advanced reasoning and agentic capabilities with exceptional efficiency. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token, achieving a generation throughput of 100–300 tokens per second. This design allows it to rival the reasoning depth of top-tier proprietary models while maintaining the agility required for real-time interaction.

Key Insights & Metrics

Pricing
Free
Cost structure
Version
1.0
Current release version
Hardware
High-end consumer hardware (e.g., Mac Studio M4 Max, NVIDIA DGX Spark)
Compute requirements
Category
Open Source
Licensing model
Region
China
Primary region

Key Features

  • Deep reasoning at speed with 3-way Multi-Token Prediction (MTP-3)
  • Robust engine for coding and agentic tasks with scalable reinforcement learning framework
  • Efficient long-context processing with 256K context window using Sliding Window Attention (SWA)
  • Accessible local deployment on high-end consumer hardware

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