# ![StepFun logo](https://models.dev/logos/stepfun-ai.svg)StepFun

Access 2 StepFun models through Mastra's model router. Authentication is handled automatically using the `STEPFUN_API_KEY` environment variable.

Learn more in the [StepFun documentation](https://platform.stepfun.ai/docs/en/step-plan/integrations/open-code).

```bash
STEPFUN_API_KEY=your-api-key
```

```typescript
import { Agent } from "@mastra/core/agent";

const agent = new Agent({
  id: "my-agent",
  name: "My Agent",
  instructions: "You are a helpful assistant",
  model: "stepfun-ai/step-3.5-flash"
});

// Generate a response
const response = await agent.generate("Hello!");

// Stream a response
const stream = await agent.stream("Tell me a story");
for await (const chunk of stream) {
  console.log(chunk);
}
```

> **Info:** Mastra uses the OpenAI-compatible `/chat/completions` endpoint. Some provider-specific features may not be available. Check the [StepFun documentation](https://platform.stepfun.ai/docs/en/step-plan/integrations/open-code) for details.

## Models

| Model                            | Context | Tools | Reasoning | Image | Audio | Video | Input $/1M | Output $/1M |
| -------------------------------- | ------- | ----- | --------- | ----- | ----- | ----- | ---------- | ----------- |
| `stepfun-ai/step-3.5-flash`      | 256K    |       |           |       |       |       | $0.10      | $0.29       |
| `stepfun-ai/step-3.5-flash-2603` | 256K    |       |           |       |       |       | $0.10      | $0.30       |

## Advanced configuration

### Custom headers

```typescript
const agent = new Agent({
  id: "custom-agent",
  name: "custom-agent",
  model: {
    url: "https://api.stepfun.ai/step_plan/v1",
    id: "stepfun-ai/step-3.5-flash",
    apiKey: process.env.STEPFUN_API_KEY,
    headers: {
      "X-Custom-Header": "value"
    }
  }
});
```

### Dynamic model selection

```typescript
const agent = new Agent({
  id: "dynamic-agent",
  name: "Dynamic Agent",
  model: ({ requestContext }) => {
    const useAdvanced = requestContext.task === "complex";
    return useAdvanced
      ? "stepfun-ai/step-3.5-flash-2603"
      : "stepfun-ai/step-3.5-flash";
  }
});
```