# Opencode Antigravity Auth Setup

> Configure OpenCode + opencode-antigravity-auth plugin to use Google OAuth (Antigravity) for free Gemini/Claude usage; includes auth-store gotchas, verified workaround, and troubleshooting with logs.

- Skill: `tankygranny05/opencode-antigravity-auth-setup` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add tankygranny05/opencode-antigravity-auth-setup`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tankygranny05/opencode-antigravity-auth-setup/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: tankygranny05 (https://skillmd.com/u/tankygranny05)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/tankygranny05/opencode-antigravity-auth-setup

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# Opencode Antigravity Auth Setup
*[Created by Codex: 019ba92d-c995-77c0-b090-e9109492f53b]*

## Overview

Enable OpenCode to call Antigravity-backed models (Gemini 3 + Claude) using Google OAuth tokens, without API keys, via the `opencode-antigravity-auth` plugin.

## Key Findings (What Broke)

- OpenCode stores provider credentials in `~/.local/share/opencode/auth.json`.
- OpenCode only runs the plugin’s `auth.loader` for `google` if a `google` credential already exists in that auth store.
- If there is **no** `google` credential, OpenCode uses bundled `@ai-sdk/google`, which requires `GOOGLE_GENERATIVE_AI_API_KEY` and fails with `AI_LoadAPIKeyError`.
- `opencode auth login google` is **not** a provider shortcut. `opencode auth login [url]` treats the arg as a URL and tries `/.well-known/opencode` (so `google` causes `ERR_INVALID_URL`).

## Workflow (Verified)

### 1) Install/enable plugin + models

- Ensure `~/.config/opencode/opencode.json` contains:
  - `"plugin": ["opencode-antigravity-auth@beta"]`
  - provider `"google"` models using the `antigravity-` prefix (recommended).
- Confirm models are visible:
  - `opencode models google`

### 2) Create a `google` OAuth credential (required for plugin loader)

- Run `opencode auth login` (no args).
- Select provider: `Google`.
- Select method: `OAuth with Google (Antigravity)`.
- Verify:
  - `opencode auth list` shows `Google oauth`.

### 3) Bootstrap workaround (verified)

If `~/.config/opencode/antigravity-accounts.json` already exists (refresh tokens saved) but `opencode auth list` shows no credentials, bootstrap the `google` OAuth entry:

```bash
python ~/.codex/skills/opencode-antigravity-auth-setup/scripts/bootstrap_opencode_google_oauth.py
```

This writes a minimal stub to `~/.local/share/opencode/auth.json`:
- `google.type=oauth`
- `google.refresh="<refreshToken>|<projectId>|<managedProjectId>"`
- `google.access=""`, `google.expires=0` (the plugin refreshes on first use)

### 4) Run a model

```bash
opencode run "hello" --model=google/antigravity-gemini-3-pro
```

## Troubleshooting

### Symptom: `AI_LoadAPIKeyError` / “Google Generative AI API key is missing”

- Cause: plugin loader not running (no `google` credential in `~/.local/share/opencode/auth.json`)
- Fix: run Workflow step (2) or (3)

### Symptom: OpenCode shows “Waiting for authorization…” forever

- Use the manual fallback flow (CLI prompt), or use the bootstrap script above.
- Check whether OpenCode actually stored the credential:
  - `opencode auth list`

### Symptom: `opencode auth login google` fails

- Expected. Use `opencode auth login` without args.

## Reference (Investigation)

- Read the investigation handoff at `references/investigation-opencode-antigravity-auth.md`.