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StepFun: Step 3.5 Flash

stepfun/step-3.5-flash:free

Model weights

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.

Modalities

Price

Free

Context

256K

Released

Jan 29, 2026

About StepFun: Step 3.5 Flash

OpenRouter makes StepFun: Step 3.5 Flash available through a unified, OpenAI-compatible API using the model ID stepfun/step-3.5-flash.

StepFun: Step 3.5 Flash accepts text and returns text. It has a 256,000-token context window.

It was released on January 29, 2026.

More models from StepFun

  • Step 3.7 Flash

Frequently asked questions

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.

Yes. The pricing shown on this page for Step 3.5 Flash is zero, so you are not charged for prompt or completion tokens. Free endpoints are rate limited — see the rate limit docs.

Step 3.5 Flash has a 256,000 token context window.

Step 3.7 Flash is another text model from StepFun.

Step 3.5 Flash was released on January 29, 2026.