It was called Google AI Studio and it was supposed to become available on both Android and iOS. The app was listed in the Google Play Store and the App Store as a pre-order, and about 800,000 people actually pre-ordered it, so clearly there was some interest for it out there. Still, Google's AI Studio team decided to "take an entirely different approach", "instead of asking you to download yet another app". So, what will happen is that the Google AI Studio functionality will be integrated into Gemini on both mobile and desktop. So if you've been waiting for a Google AI Studio mobile app, keep an eye on Gemini as it should get the same functionality soon.