it seems i have the same problem. i thought its my fault (still a high possibility), but after wasting hours with claude, the error seems to be something different.
i am having the very same problem as sebastiano_gadaleta does. thanks to claude, here is a better summary i could have ever done:
All agent requests fail with HTTP 400 Bad Request. The project ID is empty in the API request.
Error:
Trajectory ID: 47e9de86-f3a0-421e-be69-5526e82f...
Error: HTTP 400 Bad Request
TraceID: 0xb42f6a66b72c...
Message: "Invalid project resource name projects/"
Status: INVALID_ARGUMENT
Environment:
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OS: Windows
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Antigravity: latest version (fresh install)
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Account: personal Gmail with 2FA enabled
What I’ve already tried:
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Enabled 2-factor authentication
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Created a project in Google Cloud Console
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Complete uninstall and fresh reinstall
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Deleted all config folders (%APPDATA%\Antigravity, %LOCALAPPDATA%\Antigravity, .gemini, .antigravity)
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Selected “Fresh Start” during setup (no import from VS Code/Cursor)
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Signed out and back in multiple times
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Opened a completely empty folder as workspace
None of the above resolved the issue. The project ID remains empty in the API request. This appears to be a backend provisioning issue.
Thats why i request a backend reset as well. thanks 
edit: there is another much bigger thread already: Critical Bug: Persistent HTTP 400 "Invalid project resource name projects/" even after Gmail switch - #91 by paulot