copilot-claude-proxy

A small Go proxy that exposes GitHub Copilot as an Anthropic-compatible API.

If you already pay for GitHub Copilot, you can use it as the backend for Claude Code instead of an Anthropic API key. Run the proxy, point Claude Code at it, and everything works as usual. Copilot understands the same API that Claude Code speaks, so the proxy doesn't need to translate anything: it just logs you into GitHub and passes your requests along.

Installation

Homebrew (macOS and Linux)

$ brew install fabriziosestito/tap/copilot-claude-proxy

Pre-built binaries

Download the archive for your OS/architecture (including Windows) from the GitHub Releases page.

go run

No installation needed; requires Go 1.25 or newer. Used throughout this README.

Quick start

Run it with go run (Go 1.25 or newer), or use the copilot-claude-proxy pre-built binary.

Authenticate with GitHub (device flow; opens your browser automatically):

$ go run github.com/fabriziosestito/copilot-claude-proxy/cmd/copilot-claude-proxy@latest auth

Generate the Claude Code configuration (interactive model selection):

$ go run github.com/fabriziosestito/copilot-claude-proxy/cmd/copilot-claude-proxy@latest setup

Start the proxy and Claude Code together:

$ go run github.com/fabriziosestito/copilot-claude-proxy/cmd/copilot-claude-proxy@latest run

run shuts the proxy down when Claude Code exits. To keep the proxy up across sessions, use start instead:

$ go run github.com/fabriziosestito/copilot-claude-proxy/cmd/copilot-claude-proxy@latest start

Then, in another terminal:

$ claude

Commands

Command	Description
auth	GitHub device-flow login; opens the browser and stores the token in the OS keyring
logout	Remove the stored token from the OS keyring
start	Run the proxy server (default 127.0.0.1:4141)
run	Run the proxy and Claude Code together, stopping the proxy when Claude Code exits
setup	Generate Claude Code configuration pointing at this proxy
models	List the models available on your Copilot account

start options

Flag	Default	Description
--port, -p	4141	Listen port
--host, -H	127.0.0.1	Bind host
--account-type, -a	auto	Copilot tier: auto, individual, business, enterprise (auto probes your plan)
--github-token, -g		Token override (also GH_TOKEN / GITHUB_TOKEN env)
--model-map		Extra aliases, repeatable: --model-map haiku=claude-haiku-4.5
--verbose, -v		Debug logging

run options

run takes every start option, waits until the proxy accepts connections, then hands the terminal to claude. Claude Code's exit status becomes the exit status of run, and Ctrl-C goes to Claude Code rather than tearing the proxy down.

Unlike start, run binds a free ephemeral port by default instead of 4141, so it never collides with a proxy that is already running; pass --port (or set COPILOT_CLAUDE_PROXY_PORT) to pin one. The session is pinned to whatever port was bound (see below), so nothing else needs to know the number.

Arguments after -- are forwarded to Claude Code:

$ copilot-claude-proxy run -- --resume

Because the proxy shares the terminal with Claude Code's UI, its log output is limited to errors. Use --log-file/-l to capture the full log instead:

Flag	Default	Description
--log-file, -l		Append proxy logs here (also COPILOT_CLAUDE_PROXY_LOG_FILE)
--no-statusline		Leave the Claude Code status line alone
--verbose, -v		Debug logging (pair with --log-file to keep the UI readable)

How the session is pinned

run passes its configuration as a JSON document on claude --settings, which Claude Code layers over ~/.claude/settings.json and over the inherited environment. That is what makes --host/--port effective: the address the proxy actually bound to wins over whatever setup recorded, so running on another port needs no second setup.

The document carries ANTHROPIC_BASE_URL, an ANTHROPIC_AUTH_TOKEN placeholder (the proxy does not authenticate its clients), and — unless --no-statusline — a status line row showing the tier, token-expiry warnings, and last resolved model. The model selection stays in ~/.claude/settings.json, so run still needs setup to have picked the models.

Variables that would override or bypass those settings are removed from Claude Code's environment, ANTHROPIC_API_KEY most importantly: Claude Code sends it as an x-api-key header even when the auth token comes from --settings, which would put a real Anthropic credential on every request to this proxy. The rest name a different endpoint or select another provider (CLAUDE_CODE_USE_BEDROCK and friends). Everything else you exported is passed through untouched.

A --settings of your own after -- is merged into this document rather than forwarded as a second flag, since Claude Code keeps only the last --settings on a command line and forwarding yours would silently drop the proxy connection. Your keys are kept except where they would route the session away from the proxy.

setup options

--model/-m and --small-model/-s skip the interactive selection (both or neither). --with-extras/-e also writes opinionated tuning vars (telemetry off, auto-compact window, and CLAUDE_CODE_ATTRIBUTION_HEADER=0, which fixes prompt caching through Copilot). --yes/-y skips the overwrite confirmation.

Known issues

claude-fable-5 occasionally switches to Chinese

claude-fable-5 has a known bug where it can start responding (and thinking) in Chinese mid-session. The fix is to pin the language in ~/.claude/CLAUDE.md so Claude Code injects it into every session:

# User preferences

- Always respond and display your thinking in English, regardless of the
  language used in project files, documentation, or code comments.

setup prints a reminder about this whenever a fable-5 model is selected.

Building from source

$ git clone https://github.com/fabriziosestito/copilot-claude-proxy
$ cd copilot-claude-proxy
$ make build

Endpoints

Route	Behavior
POST /v1/messages	Enriched passthrough to Copilot's native Anthropic Messages API (streaming and non-streaming)
POST /v1/messages/count_tokens	Local estimation (~4 chars/token, thinking blocks excluded)
GET /v1/models	Anthropic-format list of usable models
POST /api/event_logging	Swallows Anthropic SDK telemetry
GET /health	Token/catalog health (503 when degraded, for monitors)
GET /status	Session detail for the status line: tier, token TTL, last resolved model, counters (always 200)

Token storage

The GitHub OAuth token obtained by auth is stored in the operating system keyring, and logout removes it. On headless systems without a keyring, pass the token with --github-token or the GH_TOKEN/GITHUB_TOKEN environment variables instead.

License

GPL-3.0