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 NowFast large-context reasoning
Efficient moe thinking task
Speed-optimized long-context problem
256,000 tokens
256,000 tokens
$0.10 per 1M tokens
$0.30 per 1M tokens
$0.02 per 1M tokens
$15 per 1K calls
$0.19 per 1K calls