FastRouter

Access 14 FastRouter models through Mastra's model router. Authentication is handled automatically using the FASTROUTER_API_KEY environment variable.

Learn more in the FastRouter documentation.

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);
}

info

Mastra uses the OpenAI-compatible /chat/completions endpoint. Some provider-specific features may not be available. Check the FastRouter documentation for details.

Models

14 available models

Model	Context	Tools	Reasoning	Image	Audio	Video	Input $/1M	Output $/1M
fastrouter/anthropic/claude-opus-4.1	200K						$15	$75
fastrouter/anthropic/claude-sonnet-4	200K						$3	$15
fastrouter/deepseek-ai/deepseek-r1-distill-llama-70b	131K						$0.03	$0.14
fastrouter/google/gemini-2.5-flash	1.0M						$0.30	$3
fastrouter/google/gemini-2.5-pro	1.0M						$1	$10
fastrouter/moonshotai/kimi-k2	131K						$0.55	$2
fastrouter/openai/gpt-4.1	1.0M						$2	$8
fastrouter/openai/gpt-5	400K						$1	$10
fastrouter/openai/gpt-5-mini	400K						$0.25	$2
fastrouter/openai/gpt-5-nano	400K						$0.05	$0.40
fastrouter/openai/gpt-oss-120b	131K						$0.15	$0.60
fastrouter/openai/gpt-oss-20b	131K						$0.05	$0.20
fastrouter/qwen/qwen3-coder	262K						$0.30	$1
fastrouter/x-ai/grok-4	256K						$3	$15

Advanced Configuration

Custom Headers

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"
    }
  }
});

Dynamic Model Selection

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";
  }
});