# Stepfun Step 5 Preview API

> Step 5 Preview is StepFun's flagship model for agentic work, built on a sparse Mixture-of-Experts architecture with 27B active and 600B total parameters. It accepts text, image, and video input with a 1M-token context window, and supports tool calling, structured outputs, and configurable reasoning. It is designed for software engineering, long-horizon agent workflows, and professional knowledge tasks. As a preview release, its behavior may change before the stable version.

Source: https://www.sandbase.ai/models/stepfun/step-5-preview
API reference: https://www.sandbase.ai/models/stepfun/step-5-preview/docs

## Facts

- Provider: Stepfun
- Type: Language model
- Model ID: `stepfun/step-5-preview`
- Price: $1 per 1M input tokens, $2.70 per 1M output tokens
- Context window: 1M tokens, up to 64K output tokens
- Capabilities: chat, vision, reasoning, structured output, function calling
- Billing: pay per use from one SandBase balance; no provider account or subscription needed

## Call it

- Chat Completions API: `POST https://api.sandbase.ai/v1/chat/completions`

```bash
curl -X POST https://api.sandbase.ai/v1/chat/completions \
  -H "Authorization: Bearer $SANDBASE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "stepfun/step-5-preview",
  "messages": [
    {
      "role": "user",
      "content": "Hello"
    }
  ],
  "max_tokens": 2048
}'
```

## FAQ

### How do I call Stepfun Step 5 Preview through SandBase?

Create a SandBase API key, then send requests with the model ID "stepfun/step-5-preview" to Chat Completions API (/v1/chat/completions) at https://api.sandbase.ai. The request examples on this page show the exact payload.

### How much does Stepfun Step 5 Preview cost?

$1 per 1M input tokens and $2.70 per 1M output tokens, billed per request from your SandBase balance. Discounts, when available, are shown in the pricing on this page.

### What is the context window of Stepfun Step 5 Preview?

1M tokens of context, with up to 64K output tokens per response.

### Which features does Stepfun Step 5 Preview support?

Stepfun Step 5 Preview supports vision (image input), reasoning, function calling, structured output. See Specifications above for the full list.

### Do I need a separate Stepfun account?

No. One SandBase API key and balance gives you access to Stepfun Step 5 Preview and the other models in the catalog; you do not need to sign up with Stepfun separately.