Initial release: OpenAI-compatible proxy for Google Antigravity

- OpenAI /v1/chat/completions endpoint (streaming + non-streaming)
- Native Gemini passthrough /v1beta/models/{model}:generateContent endpoint
- Tool/function calling support with round-trip encoding
- Auto model name mapping (gemini-3.5-flash -> gemini-3.5-flash-low)
- OAuth token auto-refresh
- Zero pip dependencies (Python 3.10+ stdlib)
- systemd service file included
- Models: Gemini 3.1 Pro, 3 Flash, 3.5 Flash, 2.5 Pro/Flash, Claude Sonnet/Opus 4.6

.gitignore

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+__pycache__/
+*.pyc
+*.pyo
+.env
+*.token
+antigravity-oauth-token*
+.venv/
+venv/
+*.egg-info/
+dist/
+build/
+.DS_Store
+*.swp
+*.swo
+*~

LICENSE

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+MIT License
+
+Copyright (c) 2026 Usama Shehab
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Antigravity Proxy
+
+An OpenAI-compatible proxy that bridges any OpenAI-compatible client to **Google Antigravity's** internal Cloud Code Assist API. Uses the OAuth token from the [Antigravity CLI](https://antigravity.google/) (`agy`) — no API key, no billing.
+
+Access **Gemini 3.5 Flash**, **Gemini 3.1 Pro**, **Claude Sonnet 4.6**, **Claude Opus 4.6**, and more through a single local endpoint.
+
+## Features
+
+- **OpenAI-compatible** `/v1/chat/completions` endpoint (streaming + non-streaming)
+- **Native Gemini passthrough** `/v1beta/models/{model}:generateContent` endpoint
+- **Tool/function calling** support (OpenAI tools → Gemini functionDeclarations, round-tripped)
+- **Model auto-mapping** — use friendly names (`gemini-3.5-flash`), the proxy translates to backend names automatically
+- **Token auto-refresh** — OAuth token refreshed automatically when expired
+- **Zero dependencies** — pure Python 3.10+, stdlib only
+- **systemd integration** — run as a background service
+
+## Available Models
+
+| Friendly Name        | Backend Model              | Notes                          |
+|----------------------|----------------------------|--------------------------------|
+| `gemini-3.1-pro`     | `gemini-3.1-pro-low`       | Thinking level: low            |
+| `gemini-3.1-pro-high`| `gemini-3.1-pro-low`       | Thinking level: high           |
+| `gemini-3-flash`     | `gemini-3-flash`           |                                |
+| `gemini-3.5-flash`   | `gemini-3.5-flash-low`     |                                |
+| `gemini-2.5-pro`     | `gemini-2.5-pro`           |                                |
+| `gemini-2.5-flash`   | `gemini-2.5-flash`         |                                |
+| `claude-sonnet-4.6`  | `claude-sonnet-4-6`        | Via Antigravity backend        |
+| `claude-opus-4.6`    | `claude-opus-4-6-thinking` | Thinking enabled               |
+
+Model names are mapped automatically on both endpoints. You always use the friendly name in your client config.
+
+---
+
+## Prerequisites
+
+You need the **Antigravity CLI** (`agy`) installed and authenticated. The proxy reads the OAuth token that `agy` stores on disk.
+
+### Install Antigravity CLI
+
+**macOS / Linux:**
+```bash
+curl -fsSL https://storage.googleapis.com/antigravity-releases/install.sh | bash
+```
+
+**Windows:**
+Download from [antigravity.google](https://antigravity.google/) or use `winget`:
+```
+winget install Google.Antigravity
+```
+
+### Authenticate
+
+Run the CLI once to complete the Google OAuth flow:
+```bash
+agy
+```
+This opens a browser, you sign in with your Google account, and the token is saved to `~/.gemini/antigravity-cli/antigravity-oauth-token`.
+
+> **Note:** The proxy supports both consumer Google accounts and Google Workspace accounts.
+
+---
+
+## Quick Start
+
+### Option A: Run directly
+
+```bash
+git clone https://github.com/usamashehab/antigravity-proxy.git
+cd antigravity-proxy
+python3 antigravity_proxy.py
+```
+
+The proxy starts on `http://127.0.0.1:8877`.
+
+### Option B: Run as a systemd service (recommended)
+
+```bash
+# 1. Clone to a permanent location
+git clone https://github.com/usamashehab/antigravity-proxy.git ~/antigravity-proxy
+
+# 2. Copy the service file
+mkdir -p ~/.config/systemd/user
+cp ~/antigravity-proxy/antigravity-proxy.service ~/.config/systemd/user/
+
+# 3. If you use a venv, edit the ExecStart path in the service file to point to your python
+
+# 4. Reload systemd and start
+systemctl --user daemon-reload
+systemctl --user enable antigravity-proxy
+systemctl --user start antigravity-proxy
+
+# 5. Verify
+systemctl --user status antigravity-proxy
+curl http://127.0.0.1:8877/health
+```
+
+### Option C: Run with custom host/port
+
+```bash
+python3 antigravity_proxy.py --port 9000 --host 0.0.0.0
+```
+
+> **Warning:** Binding to `0.0.0.0` exposes the proxy to your network. The proxy has no authentication layer — anyone who can reach it can use your Antigravity quota. Use `127.0.0.1` unless you know what you're doing.
+
+---
+
+## Configuration
+
+### Point your client at the proxy
+
+Any OpenAI-compatible client works. Set:
+
+| Setting     | Value                          |
+|-------------|--------------------------------|
+| Base URL    | `http://127.0.0.1:8877/v1`    |
+| API Key     | `antigravity` (any string)     |
+| Model       | Any name from the table above  |
+
+#### Examples
+
+**OpenAI Python SDK:**
+```python
+from openai import OpenAI
+client = OpenAI(
+    base_url="http://127.0.0.1:8877/v1",
+    api_key="antigravity",
+)
+response = client.chat.completions.create(
+    model="gemini-3.5-flash",
+    messages=[{"role": "user", "content": "Hello!"}],
+)
+print(response.choices[0].message.content)
+```
+
+**curl:**
+```bash
+curl http://127.0.0.1:8877/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "gemini-3.5-flash",
+    "messages": [{"role": "user", "content": "Hello!"}]
+  }'
+```
+
+**Hermes Agent:**
+```bash
+hermes config set model.provider custom
+hermes config set model.base_url http://127.0.0.1:8877/v1
+hermes config set model.api_key antigravity
+hermes config set model.default gemini-3.5-flash
+```
+
+**Claude Code:**
+```bash
+export ANTHROPIC_BASE_URL=http://127.0.0.1:8877/v1
+claude  # uses claude-sonnet-4.6 through the proxy
+```
+
+**Continue / Aider / any OpenAI-compatible tool:** Set base URL to `http://127.0.0.1:8877/v1` and use any model from the table.
+
+---
+
+## Two Endpoints
+
+The proxy serves two distinct API surfaces:
+
+### 1. OpenAI Chat Completions (default)
+
+```
+POST /v1/chat/completions
+```
+
+Standard OpenAI format. Messages, tools, streaming — all supported. Use this for any OpenAI-compatible client.
+
+### 2. Native Gemini Passthrough
+
+```
+POST /v1beta/models/{model}:generateContent
+```
+
+Accepts the exact same request format as Google's `generativelanguage.googleapis.com` API. Supports `inline_data` (images), `responseSchema` (structured output), `thinkingConfig`, and everything else — all passed through untouched.
+
+Use this when you need features that don't map to OpenAI format (image inputs, structured JSON schema output, etc.).
+
+**Example — structured output with a response schema:**
+```bash
+curl http://127.0.0.1:8877/v1beta/models/gemini-3.5-flash:generateContent \
+  -H "Content-Type: application/json" \
+  -d '{
+    "contents": [{"parts": [{"text": "Extract: Ahmed is 30 years old"}]}],
+    "generationConfig": {
+      "temperature": 0,
+      "responseMimeType": "application/json",
+      "responseSchema": {
+        "type": "OBJECT",
+        "properties": {
+          "name": {"type": "STRING"},
+          "age": {"type": "NUMBER"}
+        },
+        "required": ["name", "age"]
+      }
+    }
+  }'
+```
+
+---
+
+## Management
+
+### Check health
+```bash
+curl http://127.0.0.1:8877/health
+# {"status": "ok", "service": "antigravity-proxy"}
+```
+
+### List available models
+```bash
+curl http://127.0.0.1:8877/v1/models
+```
+
+### View logs (systemd)
+```bash
+journalctl --user -u antigravity-proxy -f
+```
+
+### Restart
+```bash
+systemctl --user restart antigravity-proxy
+```
+
+### Stop
+```bash
+systemctl --user stop antigravity-proxy
+```
+
+### Token expired?
+
+If the proxy logs show authentication errors, re-authenticate with the Antigravity CLI:
+```bash
+agy  # opens browser for re-login
+systemctl --user restart antigravity-proxy
+```
+
+---
+
+## Adding / Updating Models
+
+Edit `MODEL_MAP` at the top of `antigravity_proxy.py`:
+
+```python
+MODEL_MAP = {
+    "gemini-3.5-flash": ("gemini-3.5-flash-low", None),
+    # format: "friendly-name": ("backend-name", thinking_level_or_None)
+}
+```
+
+- **Friendly name**: what clients send (e.g. `gemini-3.5-flash`)
+- **Backend name**: the model ID Antigravity's API expects (e.g. `gemini-3.5-flash-low`)
+- **Thinking level**: `"low"`, `"high"`, or `None`
+
+After editing, restart the proxy.
+
+---
+
+## How It Works
+
+```
+Your Client (OpenAI format)
+    │
+    ▼
+Antigravity Proxy (localhost:8877)
+    │  ┌─ Translates OpenAI → Gemini format
+    │  ├─ Manages OAuth token (auto-refresh)
+    │  └─ Wraps in Antigravity envelope
+    │
+    ▼
+cloudcode-pa.googleapis.com (Google's internal Code Assist API)
+    │
+    ▼
+Gemini / Claude models
+```
+
+The proxy:
+1. Reads the OAuth token from `~/.gemini/antigravity-cli/antigravity-oauth-token`
+2. Refreshes it automatically via `oauth2.googleapis.com` when expired
+3. Discovers your Cloud Code Assist project ID via `v1internal:loadCodeAssist`
+4. Wraps each request in the Antigravity envelope (`{project, model, request, requestType}`)
+5. Forwards to `v1internal:generateContent` (or `streamGenerateContent`)
+6. Unwraps the response and converts back to OpenAI format
+
+---
+
+## Requirements
+
+- Python 3.10+
+- Antigravity CLI (`agy`) installed and authenticated
+- No pip dependencies — stdlib only
+
+---
+
+## FAQ
+
+**Is this legal?**
+
+The proxy uses the same OAuth token and API endpoints that the Antigravity CLI itself uses. It does not bypass authentication or payment — you still need a valid Google account with Antigravity access. Multiple similar projects exist on GitHub. That said, Google's terms of service may restrict programmatic API access. Use at your own discretion.
+
+**Does it support streaming?**
+
+Yes. Both SSE streaming (`stream: true`) on the OpenAI endpoint and the native Gemini stream endpoint.
+
+**Can I use it with images?**
+
+Yes, through the native Gemini passthrough endpoint (`/v1beta/models/{model}:generateContent`). Send `inline_data` with base64-encoded images, exactly like Google's API. The OpenAI chat endpoint does not currently support image inputs.
+
+**Is there a rate limit?**
+
+Rate limits are determined by Google's Antigravity quota, not the proxy. The proxy itself is multithreaded and has no concurrency limit.
+
+**Does the token expire?**
+
+Yes, the OAuth access token expires (~1 hour). The proxy auto-refreshes it using the refresh token. The refresh token itself can expire if unused for extended periods — re-run `agy` if that happens.
+
+---
+
+## License
+
+MIT

antigravity-proxy.service

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+[Unit]
+Description=Antigravity OpenAI-Compatible Proxy
+After=network.target
+
+[Service]
+Type=simple
+ExecStart=/usr/bin/python3 %h/antigravity-proxy/antigravity_proxy.py --port 8877 --host 127.0.0.1
+Restart=on-failure
+RestartSec=5
+Environment=HOME=%h
+
+[Install]
+WantedBy=default.target