StepFun: Step 3.5 Flash

stepfun/step-3.5-flash

Created Jan 29, 2026256,000 context

$0.10/M input tokens$0.30/M output tokens

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

stepfun/step-3.5-flash

Created Jan 29, 2026256,000 context

$0.10/M input tokens$0.30/M output tokens

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.

Recent activity on Step 3.5 Flash

Total usage per day on OpenRouter

Prompt

55.5M

Reasoning

6.89M

Completion

1.13M

Prompt tokens measure input size. Reasoning tokens show internal thinking before a response. Completion tokens reflect total output length.