# Anthropic API Support - Implementation Summary

## Overview

Vandamme Proxy now supports full compatibility with Anthropic APIs through two modes:
1. **OpenAI Mode**: Converts between Claude and OpenAI formats (existing functionality)
2. **Anthropic Mode**: Direct passthrough for Anthropic-compatible APIs without conversion

## Implementation Details

### New Components Added

1. **AnthropicClient** (`src/core/anthropic_client.py`)
   - Direct passthrough client for Anthropic-compatible APIs
   - Handles streaming and non-streaming requests
   - Proper SSE (Server-Sent Events) support
   - Error handling and classification

2. **Models Endpoint** (`/v1/models`)
   - Lists available models from providers
   - Returns Claude models for Anthropic-format providers
   - Transforms OpenAI models to Claude format for OpenAI providers
   - Falls back to common models if provider doesn't support /models

3. **Enhanced Health Check** (`/health`)
   - Shows all configured providers
   - Displays provider API formats (openai/anthropic)
   - Indicates which provider is the default
   - Shows configuration status for each provider

### Configuration

#### Provider API Format
Each provider can be configured with `api_format`:
```bash
# OpenAI format (default)
OPENAI_API_FORMAT=openai

# Anthropic format (direct passthrough)
ANTHROPIC_API_FORMAT=anthropic
```

#### Multiple Providers
```bash
# OpenAI Provider
OPENAI_API_KEY=sk-...
OPENAI_API_FORMAT=openai

# Anthropic Direct Provider
ANTHROPIC_API_KEY=sk-ant-...
ANTHROPIC_BASE_URL=https://api.anthropic.com
ANTHROPIC_API_FORMAT=anthropic

# AWS Bedrock
BEDROCK_API_KEY=...
BEDROCK_BASE_URL=https://bedrock-runtime.us-east-1.amazonaws.com
BEDROCK_API_FORMAT=anthropic
```

### Usage

#### Provider Selection
1. **Default Provider**: Uses `VDM_DEFAULT_PROVIDER` setting
   ```bash
   claude --model claude-3-5-sonnet-20241022
   ```

2. **Provider Prefix**: Specify provider in model name
   ```bash
   claude --model anthropic:claude-3-5-sonnet-20241022
   claude --model openai:gpt-4o
   claude --model bedrock:anthropic.claude-3-sonnet-20240229-v1:0
   ```

#### Supported Endpoints
- `POST /v1/messages` - Chat completions
- `POST /v1/messages/count_tokens` - Token counting
- `GET /v1/models` - List available models
- `GET /health` - Health check with provider status
- `GET /test-connection` - Test API connectivity

### Test Coverage

Added comprehensive tests in `tests/test_anthropic_passthrough.py`:
- Provider configuration and API format loading
- Client selection based on API format
- Models endpoint for both formats
- Health check provider status
- Message format validation

### Documentation

1. **Updated CLAUDE.md** with:
   - Architecture changes
   - Dual-mode operation explanation
   - Provider configuration examples
   - Authentication clarification

2. **Created Configuration Examples**:
   - `examples/anthropic-direct.env`
   - `examples/aws-bedrock.env`
   - `examples/google-vertex.env`
   - `examples/multi-provider.env`

## Key Benefits

1. **Performance**: No format conversion overhead for Anthropic-compatible APIs
2. **Compatibility**: Works with any Anthropic-compatible endpoint
3. **Flexibility**: Easy switching between providers per request
4. **Transparency**: Clear visibility into provider configuration
5. **Future-Proof**: Extensible to support more providers

## Authentication Clarification

- **Proxy Authentication** (`ANTHROPIC_API_KEY`): Controls access TO the proxy
- **Provider Authentication** (e.g., `OPENAI_API_KEY`): Controls access to provider APIs
- These are completely separate and independent

## Testing

Run the Anthropic-specific tests:
```bash
python -m pytest tests/test_anthropic_passthrough.py -v
```

All tests pass successfully, confirming the implementation works as expected.
