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.

Quick start

Run it with go run (Go 1.25 or newer).

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

Run the proxy:

$ 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)
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

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

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