I've always pulled my Gemini API keys from AI Studio; like, I'm sure, most of you did. A few days ago I got a call from a client telling me the AI features in my app had stopped working. I logged in and confirmed it: something was wrong with my billing. So I checked my Google Cloud account to see whether the credits had run out, but there was still a big chunk left before I'd have to start paying. I created a fresh API key and tried to link it to that billing account, and it failed.
After some digging, the answer was blunt: that workflow is gone. You can no longer spend Google Cloud credits in AI Studio.
Google has split the billing worlds apart. The Gemini Developer API (the one you get keys for in AI Studio) now runs on its own billing track. The headline change that bit a lot of people: if you created your account after March 2, 2026, the $300 free "Welcome" credits can no longer be spent on Gemini API / AI Studio usage at all, and existing accounts like mine found the old credit link quietly severed too. They explicitly say those credits can still be used on other Google Cloud products in the Google Cloud console, and that's the crack in the wall we're going to walk through.
And "other Google Cloud products" includes Vertex AI, Google's managed platform for running the very same Gemini models. So the move is simple: stop using AI Studio keys and start calling Gemini through Vertex AI. Same models, different door, and that door still takes your Cloud credits.
