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StepFun · Language model

Step 3.5 Flash

stepfun/step-3.5-flash
  • Language
Released Jan 29, 2026

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....

Specifications

Context window
262,144 tokens
Max output
65,536 tokens
Input
text
Output
text
Reasoning
always on
Tokenizer
Other

Supported parameters

Accepted by the model and forwarded as-is by the gateway.

  • frequency_penalty
  • max_tokens
  • reasoning
  • temperature
  • tool_choice
  • tools
  • top_k
  • top_p

Use it

POST /api/v1/chat/completions · MCP chat · full reference

curl https://omnirail.org/api/v1/chat/completions \
  -H "Authorization: Bearer $OMNIRAIL_KEY" -H "Content-Type: application/json" \
  -d '{"model":"stepfun/step-3.5-flash","messages":[{"role":"user","content":"Hello"}],"max_tokens":300}'