Is Step 3.5 Flash available on FastMetal?

Not at the moment. GLM 5.3 Flash, from the same lab, is available on the FastMetal API today.

What is the context window of Step 3.5 Flash?

256,000 tokens, shared between the prompt and the response.

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StepFun

stepfun/step-3-5-flash

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Step 3.5 Flash

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.

1/29/2026

256,000 tokens

Specifications

Modalities

Input

text

Output

text

Supported Parameters

frequency_penalty

include_reasoning

max_tokens

reasoning

stop

temperature

tools

top_p

Max Output Tokens

256,000

Reasoning Configuration

Default: Thinking on
Turning thinking off: Not possible (always thinks)

How to control thinking, and what it costs

Data policy

Prompt retention: Unknown — we could not confirm
Training: Unknown — not declared

"Unknown" does not mean "safe". It means we could not confirm it.

Whether a provider trains on prompts is a declared value from our terms with them. Retention is determined from the upstream listing for every host this model can reach. Neither is guessed.

Frequently asked questions

Is Step 3.5 Flash available on FastMetal?: Not at the moment. GLM 5.3 Flash, from the same lab, is available on the FastMetal API today.
What is the context window of Step 3.5 Flash?: 256,000 tokens, shared between the prompt and the response.

Models you can use on FastMetal