OpenAI API for Anthropic (Claude && Claude Code)

This package is a translation layer that allows you to use the OpenAI API interface to interact with Anthropic's Claude models. Anthropic is known for its own data models and API structure that is not compatible with OpenAI's API spec. This package bridges that gap by mapping OpenAI public API surface to Anthropic's API including models, endpoints, and parameters and data classes. [anthropic_sdk_dart](https://pub.dev/packages/anthropic_sdk_dart) is used under the hood to communicate with Anthropic's API.

Installation

Add the following to your pubspec.yaml file:

dependencies:
  openai_anthropic: ^0.1.0

Then run flutter pub get or dart pub get to install the package.

Usage

Generating OAuth credentials

Run following command to start the OAuth flow and generate credentials JSON. Follow the instructions in the terminal to complete the flow. This will generate a claude_code_credentials.json file in the current directory as well as print the credentials JSON in the terminal which you can set as an environment variable.

dart pub run openai_anthropic:generate

Use AnthropicOpenAIClient class instead of OpenAIClient and the rest of the OpenAI API remains the same. Refer openai_dart package documentation for more details on how to use the OpenAI API.

import 'package:openai_anthropic/openai_anthropic.dart';

final apiKey = Platform.environment['ANTHROPIC_API_KEY'];
final client = AnthropicOpenAIClient(apiKey: apiKey);

Chat

final res = await client.createChatCompletion(
  request: CreateChatCompletionRequest(
    model: ChatCompletionModel.modelId('gpt-5'),
    messages: [
      ChatCompletionMessage.developer(
        content: 'You are a helpful assistant.',
      ),
      ChatCompletionMessage.user(
        content: ChatCompletionUserMessageContent.string('Hello!'),
      ),
    ],
  ),
);
print(res.choices.first.message.content);
// Hello! How can I assist you today?

Refer openai_dart package documentation for more details on how to use the OpenAI API.

Using Claude Code Client

// Using credentials JSON from env.
final credentialsJson = Platform.environment['CLAUDE_CODE_CREDENTIALS'];
final credentials = ClaudeCodeCredentials.fromJson(jsonDecode(credentialsJson!));
final client = ClaudeCodeOpenAIClient(credentials: credentials);

You can also pass a tokenStore instead of credentials for more control over how tokens are stored and refreshed. To do so, extend ClaudeCodeTokenStore and implement the required methods.

How to use long-lived access token:

You can generate a long-lived access token by running claude setup-token command.

final token = Platform.environment['CLAUDE_CODE_TOKEN'];
final credentials = ClaudeCodeCredentials.fromToken(token);
final client = ClaudeCodeOpenAIClient(credentials: credentials);

Refreshing OAuth tokens

/// Refresh access token using refresh token
static Future<Map<String, dynamic>> refreshAccessToken(String refreshToken) async {
  final response = await http.post(
    Uri.parse(ClaudeOAuthConfig.tokenUrl),
    headers: ClaudeOAuthConfig.defaultHeaders,
    body: jsonEncode({
      'grant_type': 'refresh_token',
      'client_id': ClaudeOAuthConfig.clientId,
      'refresh_token': refreshToken,
    }),
  );

  if (response.statusCode != 200) {
    throw Exception('Token refresh failed: ${response.body}');
  }

  final Map<String, dynamic> tokens = Map<String, dynamic>.from(jsonDecode(response.body) as Map);
  tokens['expires_at'] = DateTime.timestamp().add(Duration(seconds: tokens['expires_in'])).millisecondsSinceEpoch;
  return tokens;
}