Step 3.5 Flash
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.
stepfun/step-3.5-flash
- Context
- 262k tokens
- Completion cap
- 65,536
- Tools
- Yes
- JSON
- No
- Released
- 2026-01-29
Call it from Geek Hub
Same OpenAI SDK. Change the base URL and the model id.
curl https://api.geekhub.mx/v1/chat/completions \
-H "Authorization: Bearer $GEEKHUB_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "stepfun/step-3.5-flash",
"messages": [{"role": "user", "content": "Hola"}]
}'Frequently asked questions
- What is Step 3.5 Flash?
- 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. Step 3.5 Flash runs on the Geek Hub API (OpenAI-compatible). Model id: stepfun/step-3.5-flash.
- Is Step 3.5 Flash free?
- No. Input is $0.109 per 1M tokens and output is $0.327 per 1M tokens on Geek Hub (markup included).
- What is the context length of Step 3.5 Flash?
- Step 3.5 Flash has a 262k tokens context window. It supports up to 65,536 completion tokens.
- Does Step 3.5 Flash support tool calling and structured outputs?
- Step 3.5 Flash accepts tools and tool_choice for function calling. Structured outputs are not listed for this endpoint.
- When was Step 3.5 Flash released?
- Step 3.5 Flash was released on 2026-01-29.