Step 3.5 Flash 2603 API
About
Build advanced reasoning agents with Step 3.5 Flash 2603, a specialized AI model optimized for complex logic and chain-of-thought tasks. This model delivers cost-effective pricing at $0.10/1M input and $0.30/1M output tokens, native tool calling support, open weights architecture. Access Step 3.5 Flash 2603 via the StepFun 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
$0.10
Output
$0.30
Caching (per 1M tokens)
Read
$0.02
Frequently Asked Questions
Step 3.5 Flash 2603 by StepFun costs $0.10 per 1M input tokens and $0.30 per 1M output tokens. Cached reads cost $0.02 per 1M tokens.
Model Details
API Integration
NPM Package
@ai-sdk/openai-compatible
Environment Variables
STEPFUN_API_KEY
API Base URL
https://api.stepfun.ai/step_plan/v1