Model selection

The proxy maps Anthropic model names to GitHub Copilot’s available models, allowing you to use different Claude model tiers through your Copilot subscription.

Available models

The proxy supports all current Claude model families. Here’s the complete mapping from the proxy source:

The latest and most capable Opus model.Supported aliases:

claude-opus-4-6
claude-opus-4-6-20260214
claude-opus-4-6-latest

Maps to: claude-opus-4.6

# Launch with Opus 4.6
./scripts/launch.sh --model claude-opus-4-6

All three aliases map to the same underlying model. Use whichever naming convention you prefer.

Latest Sonnet model with enhanced capabilities.Supported aliases:

claude-sonnet-4-5
claude-sonnet-4-5-20250929
claude-sonnet-4-5-latest

Maps to: claude-sonnet-4.5

# Launch with Sonnet 4.5
./scripts/launch.sh --model claude-sonnet-4-5

Previous generation Sonnet model.Supported aliases:

claude-sonnet-4
claude-sonnet-4-20250514
claude-3-5-sonnet-20241022
claude-3-5-sonnet-latest

Maps to: claude-sonnet-4

# Launch with Sonnet 4
./scripts/launch.sh --model claude-sonnet-4

The claude-3-5-sonnet-* aliases are maintained for backward compatibility.

Previous Opus generation.Supported aliases:

claude-opus-4-5
claude-opus-4-5-20251101
claude-opus-4-5-latest
claude-opus-4-20250918 (legacy)
claude-3-opus-20240229 (legacy)
claude-3-5-opus-latest (legacy)

Maps to: claude-opus-4.5

# Launch with Opus 4.5
./scripts/launch.sh --model claude-opus-4-5

Alternative Opus variant.Supported aliases:

claude-opus-4-1
claude-opus-4-1-latest

Maps to: claude-opus-41

# Launch with Opus 4.1
./scripts/launch.sh --model claude-opus-4-1

Fast, efficient model for lighter tasks.Supported aliases:

claude-haiku-4-5
claude-haiku-4-5-20251001
claude-haiku-4-5-latest
claude-haiku-4-20250414
claude-3-5-haiku-20241022 (legacy)
claude-3-haiku-20240307 (legacy)

Maps to: claude-haiku-4.5

# Launch with Haiku 4.5
./scripts/launch.sh --model claude-haiku-4-5

Haiku is great for tasks that don’t require the full capabilities of Opus or Sonnet, with faster response times.

Model mapping implementation

The proxy uses a comprehensive mapping table to translate model names:

const MODEL_MAP = {
  // Opus 4.6
  "claude-opus-4-6": "claude-opus-4.6",
  "claude-opus-4-6-20260214": "claude-opus-4.6",
  "claude-opus-4-6-latest": "claude-opus-4.6",
  // Sonnet 4.5
  "claude-sonnet-4-5-20250929": "claude-sonnet-4.5",
  "claude-sonnet-4-5": "claude-sonnet-4.5",
  "claude-sonnet-4-5-latest": "claude-sonnet-4.5",
  // Sonnet 4
  "claude-sonnet-4-20250514": "claude-sonnet-4",
  "claude-sonnet-4": "claude-sonnet-4",
  "claude-3-5-sonnet-20241022": "claude-sonnet-4",
  "claude-3-5-sonnet-latest": "claude-sonnet-4",
  // ... and more
}

Intelligent fallback mapping

For unknown model names, the proxy uses pattern matching:

function mapModel(anthropicModel) {
  if (MODEL_MAP[anthropicModel]) return MODEL_MAP[anthropicModel]

  // Try pattern matching for unknown dated versions
  const m = anthropicModel.toLowerCase()
  if (m.includes("opus") && (m.includes("4.6") || m.includes("4-6"))) return "claude-opus-4.6"
  if (m.includes("sonnet") && (m.includes("4.5") || m.includes("4-5"))) return "claude-sonnet-4.5"
  if (m.includes("sonnet")) return "claude-sonnet-4"
  if (m.includes("opus") && (m.includes("4.5") || m.includes("4-5"))) return "claude-opus-4.5"
  if (m.includes("opus") && (m.includes("4.1") || m.includes("4-1"))) return "claude-opus-41"
  if (m.includes("haiku")) return "claude-haiku-4.5"
  if (m.includes("opus")) return "claude-opus-4.6"

  // Pass through as-is
  return anthropicModel
}

This intelligent mapping means you can use almost any Claude model name format, and the proxy will find the best match.

Switching models

Using /model command
Command-line argument
Configuration file

Within Claude Code, use the /model command to switch models interactively:

# Inside Claude Code session
/model claude-opus-4-6

This changes the model for the current session without restarting.

The /model command is the fastest way to try different models during a session.

Specify the model when launching Claude Code:

# Using launch script
./scripts/launch.sh --model claude-sonnet-4-5

# Manual launch
ANTHROPIC_BASE_URL=http://localhost:18080 \
ANTHROPIC_API_KEY=copilot-proxy \
claude --model claude-sonnet-4-5

Set a default model in your Claude Code configuration:

{
  "model": "claude-opus-4-6"
}

See the Claude Code documentation for configuration file location.

Checking available models

Query the proxy’s /models endpoint to see all available models:

curl http://localhost:18080/v1/models

{
  "data": [
    { "id": "claude-opus-4-6", "object": "model" },
    { "id": "claude-sonnet-4-5-20250929", "object": "model" },
    { "id": "claude-sonnet-4-20250514", "object": "model" },
    { "id": "claude-opus-4-5-20251101", "object": "model" },
    { "id": "claude-haiku-4-5", "object": "model" }
  ]
}

This endpoint is called by Claude Code when it starts up to discover available models.

Model selection strategies

For complex reasoning

Use: Claude Opus 4.6Best for:

Complex code refactoring
Architecture decisions
Debugging difficult issues
Writing comprehensive documentation

For balanced performance

Use: Claude Sonnet 4.5Best for:

General development tasks
Code reviews
Writing tests
Day-to-day coding assistance

For quick tasks

Use: Claude Haiku 4.5Best for:

Simple code generation
Quick questions
Syntax help
Fast iterations

For specific capabilities

Use: Sonnet 4.5 or Opus 4.5Best for:

Testing model variations
Comparing outputs
Fallback options

Request logging

The proxy logs every model mapping for transparency:

→ claude-sonnet-4-5-20250929 → claude-sonnet-4.5 | stream | 3 messages

This shows:

Left side: Model name from Claude Code
Arrow: Indicates mapping
Right side: Actual model sent to GitHub Copilot
Additional info: Streaming mode and message count

Watch these logs to verify your model selection is working correctly.

Legacy model support

The proxy maintains backward compatibility with Claude 3 naming conventions:

Claude 3 Opus

"claude-3-opus-20240229": "claude-opus-4.5"
"claude-3-5-opus-latest": "claude-opus-4.5"

Maps to Claude Opus 4.5 for compatibility.

Claude 3.5 Sonnet

"claude-3-5-sonnet-20241022": "claude-sonnet-4"
"claude-3-5-sonnet-latest": "claude-sonnet-4"

Maps to Claude Sonnet 4.

Claude 3.5 Haiku

"claude-3-5-haiku-20241022": "claude-haiku-4.5"
"claude-3-haiku-20240307": "claude-haiku-4.5"

Maps to Claude Haiku 4.5.

Using legacy model names ensures existing scripts and configurations continue to work without modification.

Troubleshooting

Model not recognized

If you use an unknown model name, the proxy will:

Check the MODEL_MAP
Try pattern matching
Pass the name through as-is

Check the proxy logs to see how your model name was mapped:

→ your-model-name → claude-opus-4.6 | stream | 2 messages

Model errors from Copilot

If Copilot rejects the model name:

✗ Copilot API error: 400 {"error": "model not found"}

This means GitHub Copilot doesn’t support that model. Try a different model from the available list.

Inconsistent model behavior

Remember that models are served by GitHub Copilot, not Anthropic. Behavior may differ slightly from the official Anthropic API.If you notice issues:

Try a different model variant
Check GitHub Copilot’s status page
Verify your Copilot subscription is active

Performance comparison

Different models have different characteristics:

Model	Speed	Quality	Best for
Claude Opus 4.6	Slower	Highest	Complex reasoning, architecture
Claude Sonnet 4.5	Fast	High	General development tasks
Claude Sonnet 4	Fast	High	Daily coding work
Claude Opus 4.5	Medium	Very High	Advanced tasks
Claude Haiku 4.5	Fastest	Good	Simple tasks, quick questions

Start with Sonnet 4.5 for most tasks, then switch to Opus 4.6 when you need deeper reasoning or to Haiku 4.5 when you need speed.

Get Started

Setup

Usage

Configuration

Guides

Available models

Model mapping implementation

Intelligent fallback mapping

Switching models

Checking available models

Model selection strategies

For complex reasoning

For balanced performance

For quick tasks

For specific capabilities

Request logging

Legacy model support

Troubleshooting

Performance comparison

Next steps

Web search

Launching Claude

Get Started

Setup

Usage

Configuration

Guides

​Available models

​Model mapping implementation

​Intelligent fallback mapping

​Switching models

​Checking available models

​Model selection strategies

For complex reasoning

For balanced performance

For quick tasks

For specific capabilities

​Request logging

​Legacy model support

​Troubleshooting

​Performance comparison

​Next steps

Web search

Launching Claude

Available models

Model mapping implementation

Intelligent fallback mapping

Switching models

Checking available models

Model selection strategies

Request logging

Legacy model support

Troubleshooting

Performance comparison

Next steps