StepFunStep 3Arena #80Jan 29, 2026
StepFun: Step 3.5 Flash (free)
Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token. It is a reasoning model that is incredibly speed efficient even at long contexts.
Context Window
256K
tokens
Max Output
256K
tokens
Released
Jan 29, 2026
Arena Rank
#80
of 305 models
Capabilities
👁Vision
🧠Reasoning
🔧Tool Calling
⚡Prompt Caching
🖥Computer Use
🎨Image Generation
Supported Parameters
Frequency Penalty
Reduce repetition
Include Reasoning
Show reasoning tokens
Max Tokens
Output length limit
Reasoning
Extended thinking
Stop Sequences
Custom stop tokens
Temperature
Controls randomness
Tool Calling
Function calling support
Top P
Nucleus sampling
Pricing Comparison
| Router | Input / 1M | Output / 1M | Cached Input / 1M |
|---|---|---|---|
| OpenRouter | Free | Free | — |
Benchmarks
Arena ELOLMSYS Chatbot Arena
1,344/1,500Model IDs
OpenRouter
stepfun/step-3.5-flash:freeHugging Facestepfun-ai/Step-3.5-Flash ↗
Tags
reasoningtool-calling