This is a submission for the Google I/O Writing Challenge

I know what Step 1 of an Android project looks like. Download Android Studio. Wait for Gradle to finish thinking, which takes longer than it should. Configure an emulator. Scaffold a project. Notice the SDK isn't the right version. Fix the SDK. Scaffold again. At this point, you have not written a single line of feature code, and you have already spent the better part of an hour.

At Google I/O 2026, Google shipped a feature in AI Studio that made me want to test whether any of that was still necessary. The claim:

Open Google AI Studio, describe the app you want to build in plain prompt, and a working native Android app - Kotlin, Jetpack Compose, installable via USB, appears in an embedded emulator on the right side of your screen.

I wanted to build exactly this. A real bill splitter. One with tip calculation, equal and percentage-based splits, and an AI-powered “smart split” that analyzes each person's order and suggests a fair breakdown using the Gemini API.

This tutorial walks through the entire build, step by step. By the end you will have a working Android app on your device and a clear picture of how the two biggest developer announcements from I/O 2026 work together in practice.

What Google Announced at I/O 2026

Two announcements matter for this build.

AI Studio Android App Builder: Build native Android apps directly in the Build tab of AI Studio. Just select “Build an Android app” and begin prompting. Apps are generated using Kotlin and Jetpack Compose, Google’s officially recommended stack. There is an embedded Android Emulator in the browser for previewing, an integrated Android Debug Bridge for installing to your phone over USB, and direct publishing to Google Play’s Internal Test Track for those with a developer account.

Gemini 3.5 Flash: The new default model across AI Studio. It surpasses Gemini 3.1 Pro on coding benchmarks and runs at 4x the output speed of other frontier models. For this tutorial, it powers the AI-driven smart split feature inside the app itself.

Prerequisites

  • A Google account
  • A browser (Chrome recommended)
  • An Android phone for final installation (optional, as we will be utilizing the in-browser emulator for this guide)
  • A free Gemini API key from aistudio.google.com/apikey

Step 1: Open AI Studio and Navigate to the Build Tab

Go to aistudio.google.com and sign in with your Google account.

In the left sidebar, click Build. You will see a prompt area, and beneath it, you will see “Build an Android app.” Click on it.

This is the entry point that went live at I/O 2026. If you do not see it, make sure you are signed in.

Step 2: The First Prompt, Basic Equal Splitter

Start simple. Paste this prompt exactly:

Hit enter. AI Studio will take about 60 to 90 seconds to generate the app.

When it finishes, the embedded Android Emulator on the right side of the screen will load the app. You will see:

  • A total bill input field
  • A people counter
  • A tip selector with the five options
  • A results card showing tip amount, total, and per-person share

This gets you roughly 75% of the way there. The remaining 25% is not visible until you interact with the app. The custom tip percentage field will likely render correctly, but not behave correctly. It appears to accept input, but the calculation does not update as you type. There is no visible submit button; the logic gap is in the event handling, not the layout.

Step 3: Fix the Custom Tip
Click the custom tip input field and then type this in the prompt box as shown:

Test it by typing a custom percentage; the results card will now update with every digit.

Step 4: Named Participants and Percentage-Based Splitting

Equal splits are the easy case. The real problem is unequal ones; someone ordered a steak, and someone had a salad, and splitting equally could feel wrong.

Prompt:

After the emulator reloads, test three specific things:

  • Add three names — Ada, Mike, and Paul. Assign percentages. The running total should update after each entry.
  • Enter percentages that sum to more than 100. The total indicator should turn red.
  • Switch back to Equal Split. The original UI should be intact: inputs, results, and tip selector.

Step 5: The Smart Split - Gemini API at Runtime
This is where the build moves from a calculator to something genuinely intelligent.

The idea: instead of the user manually entering percentages, they describe what each person ordered in plain text: “Ada had the pasta and a glass of wine, Bolu had the steak and two beers, and Kemi had the salad and water", and the app calls the Gemini API to analyze the orders and suggest a fair percentage split.

AI Studio will set this up if you prompt it correctly. First, make sure you get your Gemini API key from aistudio.google.com/apikey.

Prompt

Replace [PASTE YOUR API KEY HERE] with your actual key before sending.

AI Studio will generate the Kotlin code for the API call, the JSON parser, and the results display as shown.

After the emulator reloads, test it with the prompt shown. Tap “Analyse Orders”. After a two to three second loading indicator, you will see something like:

The model is not just dividing the bill into thirds. It is reasoning about the relative cost of what each person ordered; the steak and two beers weighed more heavily than the pasta and wine, which weighed more than the salad and water.

Step 7: Install to Your Device
When you are satisfied with the emulator results, connect your Android phone to your computer with a USB cable.

In AI Studio, click the Install button in the top right corner of the Build panel. AI Studio uses the integrated Android Debug Bridge to detect your connected device and push the APK directly to it. No separate ADB setup. No command line.

Your phone will prompt you to allow installation from an unknown source if this is the first time. Allow it. The app will appear on your home screen within about 30 seconds.

What the Final App Covers
After completing all six steps, you will have an Android app with:

  • Equal Split tab: total bill, people count, tip selector (0/10/15/20/custom), reactive calculation

  • Custom Split tab: named participants, per-person percentage inputs, running total with over/under indicator, per-person dollar share

  • Smart Split tab: free-text order description, Gemini API analysis, suggested fair percentages and dollar amounts, loading state and error handling

Where to Go Next

  • Export to Antigravity for team development: AI Studio lets you export your project directly to Google Antigravity 2.0, the new standalone agent development desktop app announced at I/O 2026. Your conversation history, project files, and environment secrets all come with you. If you want to bring in teammates or start scaling the codebase, this is the path.

  • Publish to Google Play Internal Testing: If you have a Google Play Developer account, click Connect in AI Studio and publish directly to your Internal Test Track. Share with up to 100 testers without a public listing.

  • Add receipt scanning: Gemini 3.5 Flash is multimodal. With a follow-up prompt, you can add a camera button to the Smart Split tab that lets users photograph a receipt instead of typing out the orders. The model can read the itemized list and run the same split analysis on it.

Resources