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.

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Capabilities

Thinking

Tool Use

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

Pricing

Token Costs (per 1M tokens)

Cache Miss Input

$0.10

Non-Reasoning Output

$0.30

Cache Read Input

$0.02

Tool Costs (per 1K calls)

Web Search

$15

Code Execution

$0.19

Legacy

Made legacy on

Reason

Untested

Recommended Replacement

Qwen3.6 Plus