Developers can now tap Claude Opus 4.5 and Gemini 3 without paying for API keys by pairing the open‑source coding assistant OpenCode with the Antigravity authentication plugin. The guide walks users through installing OpenCode via the bun package manager, adding the opencode‑antigravity‑auth@beta plugin to the ~/.config/opencode/opencode.json file, and signing in through Google OAuth. Once the browser login finishes, OpenCode lists providers such as Google, OpenAI, Anthropic and GitHub Copilot, allowing the user to select the Antigravity‑enabled Google option.

After updating the config with the plugin’s model definitions, launching OpenCode and pressing Ctrl + P lets the coder switch to “Claude Opus 4.5 (Antigravity)” or other supported models like Gemini 3. This shortcut bypasses the usual paid tier, giving hobbyists and small teams immediate access to high‑end large language models for code generation and debugging. As AI‑driven development tools proliferate, free‑tier workarounds lower the barrier to experimentation, potentially accelerating adoption across startups and open‑source projects.