Step 3.5 Flash (free) API
About
Build advanced reasoning agents with Step 3.5 Flash (free), a specialized AI model optimized for complex logic and chain-of-thought tasks. This model delivers available completely free of charge, native tool calling support, open weights architecture. Access Step 3.5 Flash (free) via the OpenRouter API with up to 256K output tokens.
Capabilities
Input Modalities
text
Output Modalities
text
Reasoning
Yes
Structured Output
No
Tool Use
Yes
WeightsOpen
Limits
Context Window
256K
Tokens
Input Limit
256K
Tokens
Max Output
256K
Tokens
Pricing
Standard (per 1M tokens)
Input
Free
Output
Free
Frequently Asked Questions
Step 3.5 Flash (free) by OpenRouter costs Free per 1M input tokens and Free per 1M output tokens.
Model Details
ID
stepfun/step-3.5-flash:free
Provider
OpenRouterFamily
step
Release Date
Jan 29, 2026
Knowledge Cutoff
Jan 1, 2025
API Integration
NPM Package
@openrouter/ai-sdk-provider
Environment Variables
OPENROUTER_API_KEY
API Base URL
https://openrouter.ai/api/v1