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Your provider can expose a ChatModel, an EmbeddingsModel or both.

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Dependencies

You do not need to depend on the dartantic_ai package to create a custom provider. The dartantic_interface package is all you need. 
dependencies:
  dartantic_interface: ^VERSION

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Creating a Custom Provider

Here’s a simple example of a custom provider that exposes a ChatModel: 
class EchoProvider extends Provider<
  ChatModelOptions,
  EmbeddingsModelOptions,
  MediaGenerationModelOptions
> {
  EchoProvider()
    : super(
        name: 'echo',
        displayName: 'Echo',
        defaultModelNames: {ModelKind.chat: 'echo'},
      );

  @override
  ChatModel<ChatModelOptions> createChatModel({
    String? name,
    List<Tool<Object>>? tools,
    double? temperature,
    ChatModelOptions? options,
  }) => EchoChatModel(
    name: name ?? defaultModelNames[ModelKind.chat]!,
    defaultOptions: options,
  );
  
  @override
  MediaGenerationModel<MediaGenerationModelOptions> createMediaModel({
    String? name,
    List<Tool>? tools,
    MediaGenerationModelOptions? options,
  }) => throw UnsupportedError('Media generation not supported');
  
  // ... other required methods
}

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Custom Model

Here’s a minimal chat model example: 
class EchoChatModel extends ChatModel<ChatModelOptions> {
  EchoChatModel({required super.name, ChatModelOptions? defaultOptions})
    : super(defaultOptions: defaultOptions ?? const ChatModelOptions());

  @override
  Stream<ChatResult<ChatMessage>> sendStream(
    List<ChatMessage> messages, {
    ChatModelOptions? options,
    JsonSchema? outputSchema,
  }) {
    // Echo back the last user message
    return Stream.fromIterable([
      ChatResult<ChatMessage>(
        output: ChatMessage.fromJson(
          messages.last.toJson()..['role'] = 'model',
        ),
      ),
    ]);
  }
}
With your custom provider, you can use it with an agent directly: 
final agent = Agent.forProvider(EchoProvider());
final result = await agent.send('Hello!');
print(result.output);

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Dynamic Provider Registration

If you’d like to participate in the named lookup of providers, you can add your custom provider to the factory registry: 
// Add your custom provider factory to the registry
Agent.providerFactories['echo'] = EchoProvider.new;

// Use it like any built-in provider
final agent = Agent('echo');
final result = await agent.send('Hello!');
print(result.output);
Note: The registry maps provider names to factory functions (Provider Function()), not instances. Each time a provider is requested, a fresh instance is created.

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Examples

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Next Steps