Antigravity Managed Agent: New Interactions Return 403 After Previously Working

Gemini API
1

I successfully created an Antigravity managed-agent interaction using the documented Gemini Interactions API. Replaying the exact same minimal request now consistently returns:

HTTP 403
permission_denied: The caller does not have permission

Relevant observations:

  • The API key remains valid for ordinary Gemini API requests.
  • The same key can still retrieve the previously completed interaction.
  • Only creation of new Antigravity interactions fails.
  • The request uses antigravity-preview-05-2026, environment: "remote", and a supported underlying model.
  • No warnings or restrictions appear in AI Studio or Cloud Console.
  • This is not reported as a 429 quota error.

Has managed-agent eligibility changed, or could this be an entitlement/provisioning issue? I can provide the project and interaction details privately to Google staff for investigation.