How I Lost 900 PLN on Gemini Tokens in a Subscription

I recently got a bill of around 900 PLN from Google for the Gemini API. I had set billing alerts in GCP to notify me once spending passed 50 and 100 PLN. Something went wrong anyway, and the bill climbed without a single warning.

What went wrong

First, a few days earlier I had changed the primary email address of my Google account. After that change, notifications started arriving at the new Gmail address instead of my company inbox. The alerts worked — I was just looking at a different mailbox.

Second, I was not aware that Gemini treats subscriptions differently from Claude (Anthropic) and GPT (OpenAI API). With those companies, breaching the subscription limit simply blocks your agents. Gemini bills the overage instead — tokens beyond the limit turn into an ordinary invoice.

What this means

A subscription with a limit is not the same as a subscription with a hard limit. Before you wire your agents up to an API, check what happens once the limit is crossed: a block or a charge.

Changing the primary email of a Google account also changes where billing notifications land. After such a change, verify where the alerts actually arrive before you trust them in production.

After this traumatic experience, I decided to stop using the Gemini API for agents.