Authenticate the Opencode CLI with your Antigravity (Cloud Code) account so you can use the Antigravity-backed Gemini models with your existing quota.
- Multi-Account Load Balancing - Automatically rotates between multiple Google accounts when hitting rate limits
- Endpoint Fallback - Tries 3 endpoints (daily → autopush → prod) for maximum reliability
- Google Search Tool - Built-in web search with URL analysis and source citations
- Cross-Model Conversations - Seamlessly switch between Gemini and Claude with thinking block preservation
- Automatic Token Refresh - Handles auth transparently with no manual intervention
This repo is intended to be used as a local Opencode plugin. Follow the steps below to run it from a clone of this directory.
git clone https://github.com/shekohex/opencode-google-antigravity-auth.git
cd opencode-google-antigravity-auth
bun installYou need a Google OAuth client ID and client secret to authenticate.
- Go to Google Cloud Console → APIs & Services → Credentials.
- Create an OAuth 2.0 Client ID.
- Application type: Desktop app (recommended).
- Name it anything (e.g., “Opencode Antigravity”).
- Create it and copy the client secret.
Notes:
- This plugin already includes the required client ID.
- The client secret is required at runtime and must be set as an environment variable.
This plugin requires a Google OAuth client secret at runtime. Set it as an environment variable before you authenticate or run requests:
export ANTIGRAVITY_CLIENT_SECRET="your-google-oauth-client-secret"For local development, copy .env.example to .env and load it with your preferred shell/direnv setup.
Point Opencode at this local folder using a file:// URL:
{
"$schema": "https://opencode.ai/config.json",
"plugin": ["file:///absolute/path/to/opencode-google-antigravity-auth"]
}Run:
opencode auth loginThen choose the Google provider and select OAuth with Google (Antigravity). Authenticate in the browser when prompted.
The plugin spins up a local callback listener at http://localhost:36742/oauth-callback. After approving in the browser, you’ll land on an “Authentication complete” page with no URL copy/paste required.
If that port is already in use or you’re running headless, Opencode automatically falls back to a copy/paste flow and explains what to do.
If you want load balancing across multiple Google accounts, you can add more accounts when prompted during opencode auth login. See the Multi-Account section below for details.
The plugin supports automatic rotation across multiple Google accounts to work around rate limits.
- Sticky Account Selection: Uses the same account for all requests until it hits an error
- Automatic Rotation: When rate-limited (429) or server errors (5xx), switches to next account
- Smart Recovery: Automatically re-enables accounts after rate limit timeout expires
- Email Tracking: Shows which account is in use for easy debugging
During opencode auth login, you'll be prompted to add additional accounts:
✓ Account 1 authenticated (user@gmail.com)
You have 1 account(s) configured. Add another? (y/n): y
You can add up to 10 accounts. The plugin stores account metadata in $XDG_DATA_HOME/opencode/antigravity-accounts.json (for example ~/.local/share/opencode/antigravity-accounts.json).
- High Volume Usage: If you frequently hit Antigravity rate limits
- Production Workflows: Need maximum uptime for automated tasks
- Team Environments: Share quota across multiple Google accounts
The plugin logs account switches:
[INFO] Using account 1/3 (user@gmail.com)
[INFO] Account 1/3 rate-limited, switching...
[INFO] Using account 2/3 (user2@gmail.com)
Toast notifications also appear when switching accounts.
The plugin exposes a google_search tool that allows models to fetch real-time information from the web using Google Search and URL context analysis.
Due to Gemini API limitations, native search tools (googleSearch, urlContext) cannot be combined with function declarations (custom tools like bash, read, write) in the same request. The plugin solves this by implementing google_search as a wrapper tool that makes separate API calls to Gemini with only native search tools enabled.
Agent (with custom tools: bash, read, write, etc.)
│
└── Calls google_search tool
│
└── Makes SEPARATE API call to Gemini with:
- Model: gemini-2.5-flash
- Tools: [{ googleSearch: {} }, { urlContext: {} }]
- Returns formatted markdown with sources
- Web Search: Query Google Search for real-time information
- URL Analysis: Fetch and analyze specific URLs when provided
- Source Citations: Returns grounded responses with source links
- Thinking Mode: Optional deep analysis with configurable thinking budget
The tool is automatically available to models that support tool use. Simply ask questions that require current information:
"What are the latest news about AI?"
"Summarize this article: https://example.com/article"
"What's the current stock price of AAPL?"
When you provide URLs in your query, the model will automatically extract and analyze them.
All models can use the google_search tool since it makes independent API calls:
- Gemini models (2.5 Flash, 3 Pro, 3 Flash, etc.)
- Claude models (via Antigravity proxy)
Antigravity forwards Gemini model options, including thinkingConfig:
thinkingLevelfor Gemini 3 models ("low" | "medium" | "high").thinkingBudgetfor Gemini 2.5 models (number).
{
"provider": {
"google": {
"models": {
"gemini-3-pro-preview": {
"variants": {
"high": {
"options": {
"thinkingConfig": {
"thinkingLevel": "high",
"includeThoughts": true
}
}
}
}
},
"gemini-3-flash": {
"variants": {
"medium": {
"options": {
"thinkingConfig": {
"thinkingLevel": "medium",
"includeThoughts": true
}
}
}
}
},
"gemini-claude-sonnet-4-5-thinking": {
"variants": {
"high": {
"options": {
"thinkingConfig": {
"thinkingBudget": 32000,
"includeThoughts": true
}
}
}
}
}
}
}
}
}Antigravity provides access to Claude models via gemini-claude-* model names. The plugin automatically transforms tool schemas for Claude compatibility.
gemini-claude-sonnet-4-5- Claude Sonnet 4.5gemini-claude-sonnet-4-5-thinking- Claude Sonnet 4.5 with thinkinggemini-claude-opus-4-5-thinking- Claude Opus 4.5 with thinking
When you use any Claude thinking model (models with -thinking suffix), the plugin automatically enables interleaved thinking by adding the anthropic-beta: interleaved-thinking-2025-05-14 header to your requests.
What is Interleaved Thinking?
Without interleaved thinking, Claude thinks once at the beginning and then executes all tool calls. With interleaved thinking enabled, Claude can think between tool calls, allowing it to:
- Reason about tool results before deciding what to do next
- Chain multiple tool calls with reasoning steps in between
- Make more nuanced decisions based on intermediate results
- Adapt its approach as it learns more from each tool interaction
Why This Matters for Coding Agents
AI coding tools like Opencode heavily rely on tool use (reading files, searching code, running commands). Interleaved thinking significantly improves the quality of multi-step coding tasks because Claude can:
- Read a file → think about what it found → decide which file to read next
- Run a test → analyze the failure → make a targeted fix
- Search for a pattern → reason about the results → refine the search
Automatic Enablement
You don't need to configure anything - when you use any -thinking Claude model variant, the plugin automatically:
- Detects the thinking model from the model name suffix
- Injects the
anthropic-beta: interleaved-thinking-2025-05-14header - Merges with any existing beta headers (e.g., for prompt caching)
This is enabled by default because if you're opting into extended thinking, you almost certainly want the improved reasoning that interleaved thinking provides for tool-heavy workflows.
You should copy that config to your opencode config file.
{
"$schema": "https://opencode.ai/config.json",
"plugin": ["file:///absolute/path/to/opencode-google-antigravity-auth"],
"provider": {
"google": {
"npm": "@ai-sdk/google",
"models": {
"gemini-3-pro-preview": {
"id": "gemini-3-pro-preview",
"name": "Gemini 3 Pro",
"release_date": "2025-11-18",
"reasoning": true,
"limit": { "context": 1000000, "output": 64000 },
"cost": { "input": 2, "output": 12, "cache_read": 0.2 },
"modalities": {
"input": ["text", "image", "video", "audio", "pdf"],
"output": ["text"]
},
"variants": {
"low": { "options": { "thinkingConfig": { "thinkingLevel": "low", "includeThoughts": true } } },
"medium": { "options": { "thinkingConfig": { "thinkingLevel": "medium", "includeThoughts": true } } },
"high": { "options": { "thinkingConfig": { "thinkingLevel": "high", "includeThoughts": true } } }
}
},
"gemini-3-flash": {
"id": "gemini-3-flash",
"name": "Gemini 3 Flash",
"release_date": "2025-12-17",
"reasoning": true,
"limit": { "context": 1048576, "output": 65536 },
"cost": { "input": 0.5, "output": 3, "cache_read": 0.05 },
"modalities": {
"input": ["text", "image", "video", "audio", "pdf"],
"output": ["text"]
},
"variants": {
"minimal": { "options": { "thinkingConfig": { "thinkingLevel": "minimal", "includeThoughts": true } } },
"low": { "options": { "thinkingConfig": { "thinkingLevel": "low", "includeThoughts": true } } },
"medium": { "options": { "thinkingConfig": { "thinkingLevel": "medium", "includeThoughts": true } } },
"high": { "options": { "thinkingConfig": { "thinkingLevel": "high", "includeThoughts": true } } }
}
},
"gemini-2.5-flash-lite": {
"id": "gemini-2.5-flash-lite",
"name": "Gemini 2.5 Flash Lite",
"reasoning": false
},
"gemini-claude-sonnet-4-5-thinking": {
"id": "gemini-claude-sonnet-4-5-thinking",
"name": "Claude Sonnet 4.5",
"reasoning": true,
"limit": { "context": 200000, "output": 64000 },
"modalities": {
"input": ["text", "image", "pdf"],
"output": ["text"]
},
"variants": {
"none": { "reasoning": false, "options": { "thinkingConfig": { "includeThoughts": false } } },
"low": { "options": { "thinkingConfig": { "thinkingBudget": 4000, "includeThoughts": true } } },
"medium": { "options": { "thinkingConfig": { "thinkingBudget": 16000, "includeThoughts": true } } },
"high": { "options": { "thinkingConfig": { "thinkingBudget": 32000, "includeThoughts": true } } }
}
},
"gemini-claude-opus-4-5-thinking": {
"id": "gemini-claude-opus-4-5-thinking",
"name": "Claude Opus 4.5",
"release_date": "2025-11-24",
"reasoning": true,
"limit": { "context": 200000, "output": 64000 },
"modalities": {
"input": ["text", "image", "pdf"],
"output": ["text"]
},
"variants": {
"low": { "options": { "thinkingConfig": { "thinkingBudget": 4000, "includeThoughts": true } } },
"medium": { "options": { "thinkingConfig": { "thinkingBudget": 16000, "includeThoughts": true } } },
"high": { "options": { "thinkingConfig": { "thinkingBudget": 32000, "includeThoughts": true } } }
}
}
}
}
}
}Use OpenCode's built-in logging to debug Antigravity requests:
opencode --log-level DEBUG --print-logsOr just set the log level and check the log files:
opencode --log-level DEBUGLog files are stored in ~/.local/share/opencode/logs/ (or $XDG_DATA_HOME/opencode/logs/).
- Install the plugin locally as above.
- Run
opencode auth loginand pick OAuth with Google (Antigravity). - Complete the browser flow (or copy/paste if headless).
- Issue a model request, for example:
opencode run -m google/gemini-2.5-flash -p "hello"opencode run -m google/gemini-3-pro-high -p "solve this"
- Verify responses succeed and no API key prompt appears.
To enable image input for Antigravity models in OpenCode, you must add the modalities configuration to your model definitions in opencode.json:
{
"provider": {
"google": {
"models": {
"gemini-3-pro-preview": {
"modalities": {
"input": ["text", "image"],
"output": ["text"]
}
},
"gemini-claude-sonnet-4-5-thinking": {
"modalities": {
"input": ["text", "image"],
"output": ["text"]
}
}
}
}
}
}Without the modalities.input array containing "image", OpenCode will reject image inputs with the error: "this model does not support image input". This applies to both Gemini and Claude models accessed through Antigravity.
Note: The example config in this README already includes proper modalities configuration for all models.
Gemini API requires tool names to match the pattern ^[a-zA-Z_][a-zA-Z0-9_-]*$, meaning they cannot start with numbers. The plugin automatically sanitizes tool names by prepending t_ to any tool name that starts with a digit.
For example:
21st-dev-magic_component_builder→t_21st-dev-magic_component_builder
This sanitization is transparent and automatic. However, if you encounter tool-related errors with Gemini models, you can disable problematic MCP servers in your config:
{
"provider": {
"google": {
"models": {
"gemini-3-pro-preview": {
"tools": {
"21st-dev-magic_*": false
}
}
}
}
}
}The opencode-skills plugin is currently incompatible with this plugin. Using them together may cause invalid_request_error failures, especially with Claude thinking models, due to conflicts in message history handling.
Recommended Alternative: We suggest using openskills instead, which provides similar functionality without these compatibility issues.
This project is based on:
- opencode-gemini-auth - Original Gemini OAuth implementation by @jenslys
- CLIProxyAPI - Reference implementation for Antigravity API translation
- Special thanks to Mirrowel for identifying Gemini/Claude tool behavior fixes and mitigation strategies.
You can switch between Claude and Gemini models within the same conversation session. The plugin handles the complexities of thinking block signatures with family-independent caching.
When models generate "thinking" blocks (extended reasoning), each provider signs them cryptographically. These signatures are provider-specific and cannot be validated across providers. The plugin solves this with:
- Family-Independent Cache: Signatures are cached per model family (
claudeorgemini), preventing cross-contamination - Response Caching: When a model responds with thinking, the signature is cached in that family's namespace
- Request Restoration: When sending a request, thinking blocks are restored from the same family's cache
- Foreign Removal: Thinking blocks not found in the current family's cache are removed (they're from another family)
| Transition | Thinking Preserved | Notes |
|---|---|---|
| Claude → Claude | ✅ All Claude thinking | Signatures restored from Claude cache |
| Gemini → Gemini | ✅ All Gemini thinking | Signatures restored from Gemini cache |
| Claude → Gemini | ❌ Claude thinking removed | Not in Gemini's cache |
| Gemini → Claude | ❌ Gemini thinking removed | Not in Claude's cache |
Turn 1: Claude (thinking) → "Let me analyze this..." [cached in Claude family]
Turn 2: Switch to Gemini → Claude's thinking removed, only text preserved
Turn 3: Gemini (thinking) → "Processing..." [cached in Gemini family]
Turn 4: Switch to Claude → Gemini's thinking removed, Claude Turn 1 restored ✅
Turn 5: Switch to Gemini → Claude's thinking removed, Gemini Turn 3 restored ✅
- Family isolation: Claude and Gemini thinking are cached separately
- No cross-contamination: Impossible for signatures to leak between families
- Conversation text preserved: Only thinking blocks are removed; actual response text flows through normally
- Same-provider continuity: Each family maintains its own thinking history across model switches