I am experiencing a persistent account-specific issue in Antigravity IDE.
Environment:
- Antigravity IDE (latest available version)
- Windows 11
- Same PC, same network, same project
Issue:
One specific Google account consistently fails during AI agent execution, while my other Google accounts work normally under identical conditions.
The failure occurs after the agent starts working and eventually terminates with:
HTTP 400 Bad Request
Error:
This model does not support assistant message prefill.
The conversation must end with a user message.
Additional details:
Trajectory ID: 5b3d8a07-765a-497d-bf5f-0cf81edd59..
Trace ID: 0x87a18092f1db24..
Troubleshooting already performed:
- Restarted Antigravity IDE
- Restarted Windows
- Started new conversations
- Same project tested
- Same IDE installation
- Same internet connection
- Same machine
- Other Google accounts work perfectly
- Only one account consistently reproduces the error
Expected behavior:
The AI agent should execute normally, as it does with my other Google accounts.
Actual behavior:
The agent terminates with HTTP 400 and the “assistant message prefill” error.
This appears to be an account-specific backend issue rather than an installation or local configuration problem.
