FastRouter

FASTROUTER_API_KEY=your-api-key

import { Agent } from "@mastra/core";
 
const agent = new Agent({
  name: "my-agent",
  instructions: "You are a helpful assistant",
  model: "fastrouter/anthropic/claude-opus-4.1"
});
 
// 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);
}

const agent = new Agent({
  name: "custom-agent",
  model: {
    url: "https://go.fastrouter.ai/api/v1",
    id: "fastrouter/anthropic/claude-opus-4.1",
    apiKey: process.env.FASTROUTER_API_KEY,
    headers: {
      "X-Custom-Header": "value"
    }
  }
});

const agent = new Agent({
  name: "dynamic-agent",
  model: ({ runtimeContext }) => {
    const useAdvanced = runtimeContext.task === "complex";
    return useAdvanced 
      ? "fastrouter/x-ai/grok-4"
      : "fastrouter/anthropic/claude-opus-4.1";
  }
});