StepFun

Access 3 StepFun models through Mastra's model router. Authentication is handled automatically using the STEPFUN_API_KEY environment variable.

Learn more in the StepFun documentation.

.env

STEPFUN_API_KEY=your-api-key

src/mastra/agents/my-agent.ts

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

const agent = new Agent({
  id: "my-agent",
  name: "My Agent",
  instructions: "You are a helpful assistant",
  model: "stepfun/step-1-32k"
});

// 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 for details.

Models

3 available models

Model	Context	Tools	Reasoning	Image	Audio	Video	Input $/1M	Output $/1M
stepfun/step-1-32k	33K						$2	$10
stepfun/step-2-16k	16K						$5	$16
stepfun/step-3.5-flash	256K						$0.10	$0.29

Advanced Configuration

Custom Headers

src/mastra/agents/my-agent.ts

const agent = new Agent({
  id: "custom-agent",
  name: "custom-agent",
  model: {
    url: "https://api.stepfun.com/v1",
    id: "stepfun/step-1-32k",
    apiKey: process.env.STEPFUN_API_KEY,
    headers: {
      "X-Custom-Header": "value"
    }
  }
});

Dynamic Model Selection

src/mastra/agents/my-agent.ts

const agent = new Agent({
  id: "dynamic-agent",
  name: "Dynamic Agent",
  model: ({ requestContext }) => {
    const useAdvanced = requestContext.task === "complex";
    return useAdvanced
      ? "stepfun/step-3.5-flash"
      : "stepfun/step-1-32k";
  }
});