Step 3.5 Flash

StepFun · Released January 2026

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....

Facts and pricing

Provider

StepFun

Context window

262K tokens

Input price

1.1 credits / 1M tokens ($0.10 raw)

Output price

3.3 credits / 1M tokens ($0.30 raw)

Vision (image input)

No

Tool calling

Yes

Extended reasoning

No

Credits are what Zeplik bills: 1 credit = $0.10, computed from the raw provider rate with a 1.10x margin. Raw prices shown per 1M tokens.

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What Step 3.5 Flash is best for

• High-volume everyday tasks where speed and cost matter: summaries, drafts, quick questions
• Long documents: the 262K-token window holds lengthy reports, contracts or papers whole
• Tool use and agents: reliably calls functions, so it can search, run skills and drive workflows

StepFun family

Frequently asked questions

What is Step 3.5 Flash?

Step 3.5 Flash is an AI model by 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....

How much does Step 3.5 Flash cost on Zeplik?

Input tokens cost 1.1 credits per million and output tokens 3.3 credits per million (1 credit = $0.10; the raw provider rates are $0.10 and $0.30 per million). New accounts start with free credits.

How long can a conversation with Step 3.5 Flash be?

Step 3.5 Flash has a 262K-token context window (262,144 tokens), which covers the conversation plus any documents you attach.

Does Step 3.5 Flash support images and tools?

Step 3.5 Flash is text-only and supports tool calling.

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