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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.

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Available Models

Anthropic offers several Claude model families:

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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

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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)

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Setup Methods

Forge supports two ways to use Claude:
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

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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.

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Configuration

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API Endpoint

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

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Authentication

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

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Model Selection

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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

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Switching Models

Change models during a Forge session: 
/model claude-opus-4-20250514

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Features

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Extended Thinking

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

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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

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Tool Calling

Claude models excel at using tools:
  • File operations
  • Code execution
  • API calls
  • Multi-step workflows

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Long Context

With 200K context windows, Claude can:
  • Analyze entire codebases
  • Process long documents
  • Maintain conversation history
  • Work with large data files

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Best Practices

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

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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

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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

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Troubleshooting

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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

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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

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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

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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

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Next Steps

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