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Antigravity can complete the OAuth flow and still send initialize without the bearer token attached, which comes back as 401 Unauthorized (antigravity-cli#25).If you hit that, connect with an API key instead of OAuth.

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Install with the Kernel CLI

Run the following command:

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Configure manually

Alternatively, open the agent side panel, click the ellipsis (…) menu, and select MCP Servers, then Manage MCP Servers → View raw config. Add Kernel to the mcpServers map in mcp_config.json — ~/.gemini/config/mcp_config.json globally, or .agents/mcp_config.json for a single workspace:
Antigravity uses serverUrl for remote servers; url and httpUrl are ignored. Reload the window to pick up the change.

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Connect

Press ⌘/Ctrl , to open agent settings, go to the Customizations tab, and click Authenticate next to kernel. Authorize access in the browser window that opens, then copy the authorization code, paste it back into the settings panel, and click Submit. Antigravity stores the tokens in ~/.gemini/antigravity/mcp_oauth_tokens.json and refreshes them for you.

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Connect with an API key (workaround)

Get a project-scoped Kernel API key from the Kernel Dashboard and pass it as a header instead of authenticating. kernel mcp install --target antigravity always writes the OAuth config, so add the headers block by hand:
Leave the Authenticate button alone when using this — Antigravity sends the header on every request, including initialize.