StepFun: Step 3.5 Flash

StepFunID: stepfun/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.

Pricing per 1M Tokens

Input (Prompt)$0.10
Output (Completion)$0.30
Cache Read$0.02
Cache WriteFree
ImageN/A

Specifications

Context Length256K
Max Output Tokens256K
Input ModalitiesText
Output ModalitiesText
TokenizerOther
Instruct TypeN/A
Top Provider Context256K
Top Provider Max Output256K
ModeratedNo

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StepFun: Step 3.5 Flash (free)
InputFree
Context256K

Last updated: March 23, 2026

First tracked: March 23, 2026