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Step 3.5 Flash

Step
by StepFun AI

200B open-source reasoning engine with sparse MoE powering frontier agentic AI.

Try in Chat
Free EndpointFeb 1, 2026open license12M API calls / 30d

Specifications

Context Length
131K
131,072 tokens
Input Price
Free
per 1M tokens
Output Price
Free
per 1M tokens
Modalities
1
text→text

Capabilities

text generationchatreasoningagentic

Tags

agenticreasoningMoE

API Usage

1Router is fully OpenAI-compatible. Just set the base URL and use this model ID:

stepfun-ai/step-3.5-flash
cURL
curl https://api.1router.com/v1/chat/completions \
  -H "Authorization: Bearer $ROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "stepfun-ai/step-3.5-flash",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'