Please check the Models tab in the Antigravity settings.
There seems to be a bug related to account, capacity, or quota detection.
I suspect that some servers are unable to communicate with the microservice responsible for proper account detection, which may explain why the issue occurs randomly.
More details here:
https://discuss.ai.google.dev/t/bug-resource-exhausted-429-on-ultra-plan-despite-available-quota/126232/4
If you click Retry a few times, it starts working again…