Model Selection

The Built-in Agent uses the Vercel AI SDK, so you can use built-in model strings or pass any custom AI SDK model.

Supported Models#

Specify a model using the "provider:model" format. "provider/model" also works.

The tables list the models these docs use. The quickstart uses openai:gpt-5.4-mini. The Built-in Agent sends the model id to the provider unchanged, so other model ids from the same provider also work.

OpenAI#

const agent = new BuiltInAgent({
  model: "openai:gpt-5.4-mini",
});

Anthropic#

const agent = new BuiltInAgent({
  model: "anthropic:claude-sonnet-4-6",
});

Google#

const agent = new BuiltInAgent({
  model: "google:gemini-2.5-pro",
});

MiniMax#

const agent = new BuiltInAgent({
  model: "minimax:MiniMax-M3",
});

Environment Variables#

Set the API key for your chosen provider:

# OpenAI
OPENAI_API_KEY=sk-...

# Anthropic
ANTHROPIC_API_KEY=sk-ant-...

# Google
GOOGLE_API_KEY=...

# MiniMax
MINIMAX_API_KEY=...

# Optional: use the China endpoint
MINIMAX_BASE_URL=https://api.minimaxi.com/v1

Alternatively, pass the API key directly in your configuration:

const agent = new BuiltInAgent({
  model: "openai:gpt-5.4-mini",
  apiKey: process.env.MY_OPENAI_KEY, 
});

Custom Models (AI SDK)#

For models not in the built-in list, you can pass any Vercel AI SDK LanguageModel instance directly. First, install the provider package from its ai-v6 release line:

npm install @ai-sdk/openai@ai-v6

import { BuiltInAgent } from "@copilotkit/runtime/v2";
import { createOpenAI } from "@ai-sdk/openai"; 

const customProvider = createOpenAI({
  apiKey: process.env.MY_API_KEY, 
  baseURL: "https://my-proxy.example.com/v1", 
}); 

const agent = new BuiltInAgent({
  model: customProvider("my-fine-tuned-model"), 
});

This works with any AI SDK provider, including Azure OpenAI, AWS Bedrock, Ollama, or any OpenAI-compatible endpoint:

import { createAzure } from "@ai-sdk/azure";

const azure = createAzure({
  resourceName: "my-resource",
  apiKey: process.env.AZURE_API_KEY,
});

const agent = new BuiltInAgent({
  model: azure("my-deployment"),
});

OpenRouter, proxies, and bring-your-own LLM#

Anything that exposes an OpenAI-compatible API, including OpenRouter, a self-hosted gateway, an internal LLM proxy, Ollama, Together, Groq, Novita, or your own fine-tuned endpoint, works through the same createOpenAI({ baseURL }) pattern shown in Custom Models above. Point baseURL at the provider's OpenAI-compatible route and pass your key:

import { BuiltInAgent } from "@copilotkit/runtime/v2";
import { createOpenAI } from "@ai-sdk/openai"; 

// OpenRouter: one key, hundreds of models behind an OpenAI-compatible API
const openrouter = createOpenAI({
  apiKey: process.env.OPENROUTER_API_KEY, 
  baseURL: "https://openrouter.ai/api/v1", 
}); 

const agent = new BuiltInAgent({
  model: openrouter("anthropic/claude-sonnet-4-6"), 
});

The same shape works for any OpenAI-compatible proxy. Swap the baseURL and key. There is no CopilotKit-specific provider to install. Install @ai-sdk/openai@ai-v6 as shown in Custom Models. If the AI SDK can talk to it, the Built-in Agent can use it.

new BuiltInAgent({ model: "openai:gpt-5.4-mini" }); // built-in string
new BuiltInAgent({ model: openrouter("...") }); // any LanguageModel

How it works#

The Built-in Agent resolves model strings to AI SDK provider instances:

Both "provider:model" and "provider/model" separators are supported and work identically.