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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);
}
OpenAI Compatibility

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

Models​

ModelImageAudioVideoToolsStreamingContext Window
fastrouter/moonshotai/kimi-k2✗✗✗✓✗131,072
fastrouter/x-ai/grok-4✗✗✗✓✗256,000
fastrouter/google/gemini-2.5-flash✓✗✗✓✗1,048,576
fastrouter/google/gemini-2.5-pro✓✗✗✓✗1,048,576
fastrouter/openai/gpt-5-nano✓✗✗✓✗400,000
fastrouter/openai/gpt-4.1✓✗✗✓✗1,047,576
fastrouter/openai/gpt-5-mini✓✗✗✓✗400,000
fastrouter/openai/gpt-oss-20b✗✗✗✓✗131,072
fastrouter/openai/gpt-oss-120b✗✗✗✓✗131,072
fastrouter/openai/gpt-5✓✗✗✓✗400,000
fastrouter/qwen/qwen3-coder✗✗✗✓✗262,144
fastrouter/anthropic/claude-opus-4.1✓✗✗✓✗200,000
fastrouter/anthropic/claude-sonnet-4✓✗✗✓✗200,000
fastrouter/deepseek-ai/deepseek-r1-distill-llama-70b✗✗✗✗✗131,072

Advanced Configuration​

Custom Headers​

const agent = new Agent({
  name: "custom-agent",
  model: {
    url: "https://go.fastrouter.ai/api/v1",
    modelId: "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";
  },
});