Anthropic/Claude Setup

Configure Anthropic’s Claude models for advanced reasoning and coding tasks

Anthropic’s Claude models are known for their advanced reasoning capabilities, long context windows, and excellent performance on coding tasks. Forge supports both direct Anthropic API access and Claude Code integration.

Available Models

Anthropic offers several Claude model families:

Claude 4 Series (Latest)

• claude-sonnet-4-20250514 - Balanced performance and speed
• claude-opus-4-20250514 - Most capable for complex tasks
• claude-opus-4-1-20250805 - Enhanced reasoning capabilities
• claude-opus-4-5-20251101 - Latest flagship with advanced analysis
• claude-haiku-4-5-20251001 - Fast and efficient

Claude 3 Series

• claude-3-7-sonnet-20250219 - Enhanced third generation
• claude-3-5-haiku-20241022 - Fast and efficient
• claude-3-haiku-20240307 - Quick responses

All Claude 4 models support:

• 200K context window
• Tool calling and parallel tool execution
• Extended thinking/reasoning
• Vision (text + image input)

Setup Methods

Forge supports two ways to use Claude:

1. Direct API Access (Recommended)

1. Get Your API Key

   1. Visit Anthropic Console
   2. Sign up or log in to your account
   3. Navigate to API Keys section
   4. Create a new API key
   5. Copy your API key (starts with sk-ant-...)
2. Configure Forge

   Run the interactive login command:

   forge provider login
   

   Select Anthropic from the list and paste your API key when prompted.

3. Select a Model

   Set your default model in forge.yaml:

   model: claude-sonnet-4-20250514
   
4. Verify Connection

   Start Forge and test:

   forge
   

   Try a prompt:

   > Explain how async/await works in Rust
   

2. Claude Code Integration

Claude Code provides OAuth-based authentication for seamless integration with Anthropic’s ecosystem.

1. Initiate OAuth Flow

   forge provider login
   

   Select Claude Code from the provider list.

2. Authorize Access

   Follow the prompts to:

   1. Open the authorization URL in your browser
   2. Log in to your Anthropic account
   3. Grant Forge access to your Claude Code session
3. Complete Authentication

   Once authorized, Forge will automatically receive and store your access token.

Configuration

API Endpoint

• Messages API: https://api.anthropic.com/v1/messages
• Models List: https://api.anthropic.com/v1/models

Authentication

Anthropic uses API key authentication via the x-api-key header or OAuth tokens for Claude Code.

Model Selection

Choosing the Right Model

For Coding and Agents:

• claude-sonnet-4-20250514 - Best balance of speed and capability
• claude-opus-4-6 - Most intelligent for complex coding tasks

For Fast Responses:

• claude-haiku-4-5-20251001 - Quick, efficient responses
• claude-3-5-haiku-20241022 - Fast third-generation model

For Maximum Capability:

• claude-opus-4-5-20251101 - Enhanced reasoning and analysis
• claude-opus-4-1-20250805 - Advanced problem-solving

Switching Models

Change models during a Forge session:

/model claude-opus-4-20250514

Features

Extended Thinking

Claude 4 models support extended thinking for complex reasoning tasks. The model will show its reasoning process before providing the final answer.

Vision Capabilities

All Claude 4 models support both text and image inputs:

• Analyze code screenshots
• Process diagrams and charts
• Review UI mockups
• Examine error messages in images

Tool Calling

Claude models excel at using tools:

• File operations
• Code execution
• API calls
• Multi-step workflows

Long Context

With 200K context windows, Claude can:

• Analyze entire codebases
• Process long documents
• Maintain conversation history
• Work with large data files

Best Practices

Claude API keys should be kept secure and never committed to version control.

Rate Limits

Be aware of rate limits:

• Requests per minute: Varies by plan
• Tokens per minute: Varies by plan and model
• Check your usage dashboard for current limits

Cost Optimization

• Use Haiku models for simple tasks
• Use Sonnet for balanced performance
• Reserve Opus for complex reasoning tasks
• Monitor token usage in the console

Troubleshooting

Invalid API Key

If authentication fails:

1. Verify your API key starts with sk-ant-
2. Check that the key is active in the console
3. Ensure you have sufficient credits

Rate Limit Errors

If you hit rate limits:

1. Check your current limits in the console
2. Implement exponential backoff
3. Consider upgrading your plan
4. Spread requests over time

Token Limit Exceeded

If requests exceed token limits:

1. Reduce context size
2. Summarize previous conversation
3. Split large requests into smaller chunks
4. Use models with appropriate context windows

Deprecated: Environment Variable Setup

Using environment variables is deprecated. Please use forge provider login instead.

For backward compatibility:

# .env
ANTHROPIC_API_KEY=sk-ant-your-api-key

# forge.yaml
model: claude-sonnet-4-20250514

Next Steps

• Learn about Claude’s capabilities
• Explore prompt engineering
• Set up custom rules for your projects