copilot-proxy

Use your GitHub Copilot subscription as the backend for Claude Code.

A zero-dependency localhost proxy that translates the Anthropic Messages API into the OpenAI Chat Completions format used by GitHub Copilot's API. This lets you run claude (Claude Code CLI) powered entirely by your existing Copilot Business/Enterprise subscription — no separate Anthropic API key required.

┌────────────┐     Anthropic API      ┌───────────────┐    OpenAI API     ┌─────────────────┐
│ Claude Code │ ──────────────────────▶│ copilot-proxy │ ────────────────▶│ GitHub Copilot  │
│    (CLI)    │◀────────────────────── │  :4141        │◀──────────────── │      API        │
└────────────┘  Anthropic SSE events  └───────────────┘  OpenAI SSE      └─────────────────┘

Features

• Full API translation — Anthropic Messages API ↔ OpenAI Chat Completions, including streaming SSE
• All Claude models — Opus 4.6, Sonnet 4.6, Haiku 4.5 (and 4.5 variants)
• Tool use / function calling — Complete bidirectional translation of tool definitions and results
• Streaming — Real-time SSE event translation (OpenAI data: → Anthropic event: format)
• Multi-modal — Image content blocks translated to OpenAI image_url format
• Zero dependencies — Pure Node.js stdlib (http, https, fs, os, path, child_process)
• Auto-authentication — Discovers tokens from 5 sources with GitHub Device Flow fallback
• Token refresh — Automatic retry on 401/403 with token cache invalidation

Quick Start

One-command install

git clone https://github.com/schwarztim/copilot-proxy.git ~/.copilot-proxy
ln -sf ~/.copilot-proxy/claude-copilot ~/.local/bin/claude-copilot

Then just run:

claude-copilot

The launcher handles everything: starts the proxy, seeds the required config, and launches Claude Code.

Manual setup

# 1. Start the proxy
node proxy.mjs

# 2. Point claude at it
export ANTHROPIC_BASE_URL=http://localhost:4141
export ANTHROPIC_API_KEY=sk-ant-copilot-proxy-not-a-real-key
claude

How It Works

Authentication Chain

The proxy discovers your GitHub Copilot token automatically, checking these sources in order:

Priority	Source	Description
1	COPILOT_GITHUB_TOKEN	Environment variable override
2	OpenCode auth.json	~/.local/share/opencode/auth.json
3	macOS Keychain	Service: copilot-cli
4	GitHub CLI	gh auth token
5	Legacy config	~/.config/github-copilot/apps.json
6	Device Flow	Interactive GitHub OAuth (first-run only)

If no token is found, the proxy starts an interactive GitHub Device Flow to authenticate with the copilot scope.

Model Mapping

Claude Code sends model IDs with dashes (e.g., claude-sonnet-4-6). The Copilot API expects dots (e.g., claude-sonnet-4.6). The proxy handles this automatically, including stripping date suffixes and version tags.

Claude Code sends	Copilot receives
claude-sonnet-4-6	claude-sonnet-4.6
claude-opus-4-6	claude-opus-4.6
claude-haiku-4-5	claude-haiku-4.5
claude-sonnet-4-5-20250929	claude-sonnet-4.5
claude-opus-4-5-v1	claude-opus-4.5

Non-Claude models (GPT, Gemini) are passed through unchanged.

API Translation

The proxy performs bidirectional translation between the two API formats:

Request (Anthropic → OpenAI)

• System prompts → role: "system" messages
• Content blocks → Concatenated text or multipart content
• tool_use blocks → tool_calls array
• tool_result blocks → role: "tool" messages
• Image blocks → image_url with data URI
• stop_sequences → stop
• thinking → reasoning_effort

Response (OpenAI → Anthropic)

• choices[0].message → Anthropic message envelope
• finish_reason mapping: stop→end_turn, length→max_tokens, tool_calls→tool_use
• Token usage translation with cache token fields

Streaming (OpenAI SSE → Anthropic SSE)

• message_start → content_block_start → content_block_delta → content_block_stop → message_delta → message_stop
• delta.content → text_delta events
• delta.tool_calls → input_json_delta events with proper block lifecycle

Configuration

Environment Variable	Default	Description
COPILOT_PROXY_PORT	4141	Port the proxy listens on
COPILOT_GITHUB_TOKEN	—	Override the GitHub token
ANTHROPIC_BASE_URL	—	Set by launcher; points claude at proxy
ANTHROPIC_API_KEY	—	Set by launcher; sk-ant- prefixed key

Verbose logging

node proxy.mjs --verbose    # or -v

Logs model routing, message counts, and token usage to stderr.

Architecture

proxy.mjs (804 lines, zero dependencies)
├── Token Management      — Multi-source token discovery + caching
├── GitHub Device Flow    — Interactive OAuth for first-run auth
├── Anthropic → OpenAI    — Request translation (messages, tools, images)
├── OpenAI → Anthropic    — Response translation (non-streaming)
├── Streaming Translator  — SSE event-by-event conversion
├── HTTP Server           — Routes: /v1/messages, /v1/models, /health
└── Helpers               — Logging, JSON parsing

claude-copilot (launcher script)
├── Proxy Lifecycle       — Auto-start with health check polling
├── Config Seeding        — Onboarding wizard bypass for claude-cli
└── Exec                  — Replaces process with claude binary

Limitations

• Copilot subscription required — You need GitHub Copilot Business or Enterprise
• Rate limits — Subject to Copilot's rate limiting, not Anthropic's
• Extended thinking — Mapped to reasoning_effort: "high" (not native thinking blocks)
• Caching — Copilot doesn't support prompt caching; cache token fields are zeroed
• Beta features — Anthropic beta headers are not forwarded

Troubleshooting

Proxy won't start

cat /tmp/copilot-proxy.log
# Check if port 4141 is in use
lsof -i :4141

Authentication issues

# Verify your token works
curl -s https://api.business.githubcopilot.com/models \
  -H "Authorization: Bearer $(gh auth token)" \
  -H "Copilot-Integration-Id: copilot-developer-cli"

Claude shows onboarding wizard

# The launcher seeds this automatically, but if needed manually:
claude-copilot --version  # Triggers config seeding without starting interactive mode

Requirements

• Node.js ≥ 18
• GitHub Copilot Business or Enterprise subscription
• Claude Code CLI (claude) installed

License

MIT