Antigravity OAuth Plugin for Opencode

Authenticate the Opencode CLI with your Antigravity (Cloud Code) account so you can use the Antigravity-backed Gemini models with your existing quota.

Features

- 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

Setup

1. Add the plugin to your Opencode config:

``json
{
"$schema": "https://opencode.ai/config.json",
"plugin": ["opencode-google-antigravity-auth"]
}
`

2. Run opencode auth login.
3. Choose the Google provider and select OAuth with Google (Antigravity).
4. Authenticate with your first Google account in the browser.
5. Optional: Add more accounts for load balancing when prompted.

The plugin spins up a local callback listener on http://localhost:36742/oauth-callback, so after approving in the browser you'll land on an "Authentication complete" page with no URL copy/paste required. If that port is already taken or you're headless, the CLI automatically falls back to the copy/paste flow and explains what to do.

Multi-Account Load Balancing

The plugin supports automatic rotation across multiple Google accounts to work around rate limits.

$3

- 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

$3

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).

$3

- 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

$3

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.

Google Search Tool

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.

$3

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
`

$3

- 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

$3

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.

$3

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)

Updating

> [!WARNING]
> Opencode does NOT auto-update plugins.

To get the latest version, clear the cached plugin and let Opencode reinstall it:

`bash
rm -rf ~/.cache/opencode/node_modules/opencode-google-antigravity-auth
opencode
`

Alternatively, remove the dependency from ~/.cache/opencode/package.json if the above doesn't work.

Thinking Configuration

Antigravity forwards Gemini model options, including thinkingConfig:

* thinkingLevel for Gemini 3 models ("low" | "medium" | "high").
* thinkingBudget for Gemini 2.5 models (number).

$3

`json
{
"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
}
}
}
}
}
}
}
}
}
`

Claude Proxy Models

Antigravity provides access to Claude models via gemini-claude-* model names. The plugin automatically transforms tool schemas for Claude compatibility.

$3


- gemini-claude-sonnet-4-5 - Claude Sonnet 4.5
- gemini-claude-sonnet-4-5-thinking - Claude Sonnet 4.5 with thinking
- gemini-claude-opus-4-5-thinking - Claude Opus 4.5 with thinking

$3

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:

1. Read a file → think about what it found → decide which file to read next
2. Run a test → analyze the failure → make a targeted fix
3. 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-2025-05-14 header
- 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.

Local Development

`bash
git clone https://github.com/shekohex/opencode-google-antigravity-auth.git
cd opencode-google-antigravity-auth
bun install
`

To load a local checkout in Opencode:

`json
{
"$schema": "https://opencode.ai/config.json",
"plugin": ["file:///absolute/path/to/opencode-google-antigravity-auth"]
}
`

Example Opencode config with provider/models

You should copy that config to your opencode config file.

`json
{
"$schema": "https://opencode.ai/config.json",
"plugin": ["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 } } }
}
}
}
}
}
}
`

Debugging Antigravity Requests

Use OpenCode's built-in logging to debug Antigravity requests:

`bash
opencode --log-level DEBUG --print-logs
`

Or just set the log level and check the log files:

`bash
opencode --log-level DEBUG
`

Log files are stored in ~/.local/share/opencode/logs/ (or $XDG_DATA_HOME/opencode/logs/).

How to test with Opencode

1. Install plugin locally as above or via registry.
2. Run opencode auth login and pick Antigravity.
3. Complete browser flow (or copy/paste if headless).
4. Issue a Gemini model request, e.g. opencode run -m google/gemini-2.5-flash -p "hello" or opencode run -m google/gemini-3-pro-high -p "solve this".
5. Verify responses succeed and no API key prompt appears.

Troubleshooting

$3

To enable image input for Antigravity models in OpenCode, you must add the modalities configuration to your model definitions in opencode.json:

`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.

$3

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:

`json
{
"provider": {
"google": {
"models": {
"gemini-3-pro-preview": {
"tools": {
"21st-dev-magic_*": false
}
}
}
}
}
}
`

$3

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.

Credits

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.

Cross-Model Conversations

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.

$3

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:

1. Family-Independent Cache: Signatures are cached per model family (claude or gemini), preventing cross-contamination
2. Response Caching: When a model responds with thinking, the signature is cached in that family's namespace
3. Request Restoration: When sending a request, thinking blocks are restored from the same family's cache
4. Foreign Removal: Thinking blocks not found in the current family's cache are removed (they're from another family)

$3

| 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 |

$3

`
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 ✅
``

$3

- 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