Step 3.5 Flash
Step 3.5 Flash is an open-source foundation model built on sparse Mixture of Experts (MoE) architecture that selectively activates only 11B of its 196B parameters per token, delivering frontier reasoning and agentic capabilities with exceptional efficiency.
https://static.stepfun.com/blog/step-3.5-flash?ref=producthunt
Product Information
Updated:Mar 6, 2026
What is Step 3.5 Flash
Step 3.5 Flash is StepFun's most capable open-source foundation model, engineered to transform static models into active agents through advanced reasoning and tool-use capabilities. It supports a 256K context window and achieves 100-300 tokens/second generation throughput via 3-way Multi-Token Prediction (MTP-3). The model is designed to be accessible both through cloud APIs (via OpenRouter and StepFun Platform) and for local deployment on high-end consumer hardware like Mac Studio M4 Max and NVIDIA DGX Spark.
Key Features of Step 3.5 Flash
Step 3.5 Flash is a cutting-edge open-source foundation model developed by StepFun that uses a sparse Mixture of Experts (MoE) architecture, selectively activating only 11B of its 196B parameters per token. It features a 256K context window, achieves 100-350 tokens per second generation speed, and excels at agentic tasks, mathematical reasoning, coding, and deep research while maintaining high efficiency and accessibility for local deployment.
Efficient Parameter Usage: Uses sparse MoE architecture that activates only 11B of 196B parameters per token, enabling high performance while maintaining computational efficiency
Advanced Reasoning Capabilities: Demonstrates exceptional proficiency in managing multi-stage processes, including data ingestion, cleaning, feature construction, and results interpretation with strong performance on math and coding benchmarks
High-Speed Processing: Achieves generation throughput of 100-350 tokens per second with 256K context window support, powered by 3-way Multi-Token Prediction (MTP-3)
Local Deployment Support: Optimized for local deployment on high-end personal hardware like Apple M4 Max, NVIDIA DGX Spark, or AMD AI Max+ 395, ensuring private and secure execution
Use Cases of Step 3.5 Flash
Professional Data Analysis: Handles end-to-end data analysis tasks including data ingestion, cleaning, feature construction, and results interpretation for business intelligence applications
Deep Research Assistant: Conducts comprehensive research by planning, searching, reflecting, and writing, achieving high scores on research quality benchmarks while maintaining factual accuracy
Coding and Development: Assists in software development with high performance on coding benchmarks, capable of handling complex programming tasks and repository architecture analysis
Stock Investment Analysis: Generates professional trading recommendations by analyzing market data, technical indicators, and managing automated alerts through integration with multiple tools
Pros
High efficiency with selective parameter activation
Strong performance across multiple benchmarks
Supports local deployment for enhanced privacy
Fast inference speed with 100-350 tokens per second
Cons
Requires longer generation trajectories compared to some competitors
May experience reduced stability during distribution shifts
Limited performance in highly specialized domains
Can exhibit inconsistencies in long-horizon, multi-turn dialogues
How to Use Step 3.5 Flash
Choose access method: You can access Step 3.5 Flash through: 1) OpenRouter 2) StepFun Platform API 3) Local deployment via GGUF format
Cloud API Setup (Option 1 - OpenRouter): Sign up at OpenRouter to get your API key. Use base URL: https://openrouter.ai/api/v1 with model: stepfun/step-3.5-flash
Cloud API Setup (Option 2 - StepFun Platform): Sign up at platform.stepfun.ai (International) or platform.stepfun.com (China). Use base URL: https://api.stepfun.ai/v1 (International) or https://api.stepfun.com/v1 (China) with model: step-3.5-flash
Install OpenClaw for agent capabilities: Run: curl -fsSL https://openclaw.ai/install.sh | bash
Configure OpenClaw: 1) Run 'openclaw onboard' 2) In WebUI go to Config → Models 3) Add provider with type: openai-completions and base URL: https://api.stepfun.ai/v1
Local Deployment Setup: 1) Download model from Hugging Face: stepfun-ai/Step-3.5-Flash-FP8 or INT4 version 2) Use vLLM or llama.cpp for inference 3) Requires high-end hardware like NVIDIA DGX Spark or Apple M4 Max
Web Interface Access: Visit stepfun.ai (International) or stepfun.com (China) to use web interface
Mobile App Access: Download StepFun app from iOS App Store or Google Play Store
Join Community: Join Discord community at https://discord.gg/RcMJhNVAQc for updates and support
Step 3.5 Flash FAQs
Step 3.5 Flash is an open-source foundation model engineered for frontier reasoning and agentic capabilities. It uses a sparse Mixture of Experts (MoE) architecture, activating only 11B of its 196B parameters per token. It excels in deep reasoning, coding, and agentic tasks with generation speeds of 100-300 tokens/second.
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