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

[!CAUTION] There are reports of Google blocking accounts using this plugin, and the current Antigravity ToS (as of 2026-18-02) states that their service can't be used with third-party products.

Use this plugin at your own discretion.

Setup

Add the plugin to your Opencode config:

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

Run opencode auth login.
Choose the Google provider and select OAuth with Google (Antigravity).
Authenticate with your first Google account in the browser.
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.

How It Works

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

Setup Multiple Accounts

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).

When To Use Multi-Account

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

Monitoring

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.

How It Works

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

Features

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

Usage

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.

Supported Models

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:

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).

Examples

{
  "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.

Available Claude Models

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

Interleaved Thinking Support

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-2025-05-14 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

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:

{
  "$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.

{
  "$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:

opencode --log-level DEBUG --print-logs

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

opencode --log-level DEBUG

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

How to test with Opencode

Install plugin locally as above or via registry.
Run opencode auth login and pick Antigravity.
Complete browser flow (or copy/paste if headless).
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".
Verify responses succeed and no API key prompt appears.

Troubleshooting

Image Support

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.

Tool Name Compatibility with Gemini

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
          }
        }
      }
    }
  }
}

Compatibility with `opencode-skills`

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.

How It Works

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 (claude or gemini), 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)

Behavior Summary

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

Multi-Turn Example

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 ✅

Key Points

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

OpenCode Google Antigravity Auth

Installation

Installation

README

Antigravity OAuth Plugin for Opencode

Features

Setup

Multi-Account Load Balancing

How It Works

Setup Multiple Accounts

When To Use Multi-Account

Monitoring

Google Search Tool

How It Works

Features

Usage

Supported Models

Updating

Thinking Configuration

Examples

Claude Proxy Models

Available Claude Models

Interleaved Thinking Support

Local Development

Example Opencode config with provider/models

Debugging Antigravity Requests

How to test with Opencode

Troubleshooting

Image Support

Tool Name Compatibility with Gemini

Compatibility with `opencode-skills`

Credits

Cross-Model Conversations

How It Works

Behavior Summary

Multi-Turn Example

Key Points

Similar Items

Comments

Installation

Installation

README

Antigravity OAuth Plugin for Opencode

Features

Setup

Multi-Account Load Balancing

How It Works

Setup Multiple Accounts

When To Use Multi-Account

Monitoring

Google Search Tool

How It Works

Features

Usage

Supported Models

Updating

Thinking Configuration

Examples

Claude Proxy Models

Available Claude Models

Interleaved Thinking Support

Local Development

Example Opencode config with provider/models

Debugging Antigravity Requests

How to test with Opencode

Troubleshooting

Image Support

Tool Name Compatibility with Gemini

Compatibility with opencode-skills

Credits

Cross-Model Conversations

How It Works

Behavior Summary

Multi-Turn Example

Key Points

Similar Items

Comments

Compatibility with `opencode-skills`