Step 3.5 Flash

stepfun

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.

Try Now

Capabilities

Tool Use

Extended Thinking

Example Use Cases

Fast large-context reasoning

Efficient moe thinking task

Speed-optimized long-context problem

Technical Specifications

Context Window

256,000 tokens

Max Output

256,000 tokens

Cache Miss Cost

$0.10 per 1M tokens

Non-Reasoning Cost

$0.30 per 1M tokens

Cache Read Cost

$0.02 per 1M tokens

Web Search Cost

$15 per 1K calls

Code Execution Cost

$0.19 per 1K calls

⚠️ Legacy

Made legacy on

Reason

Untested

Recommended Replacement

Qwen3.5 Plus