AI & TechnologyFlutter Android Build Fails After AGP 9: The Fix

If a Flutter Android build fails after you move to Android Gradle Plugin 9, the cause is usually built-in Kotlin: AGP 9.0 turns it on by default, and a project or plugin that still applies kotlin-android breaks. The quick fix is two flags in android/gradle.properties. The lasting fix is to migrate the app and its plugins. Flutter 3.44 or later is needed for AGP 9, and 3.47 or later to switch built-in Kotlin on.

The facts below come from Google's AGP 9.0 release notes, Flutter's migration guides and Flutter's GitHub issues, as listed in the sources. I checked each one on October 18, 2026.

Disclosure: App369 is my studio. I build and fix Flutter apps, and the last section mentions what I sell. Google doesn't pay me for anything on this page.

What AGP 9.0 changes

Google's release notes list a major release with API and behavior changes. The ones that matter for a Flutter app:

Source for the table: AGP 9.0.1 release notes.

Google's notes say you no longer apply org.jetbrains.kotlin.android or kotlin-android to compile Kotlin, and that the plugin is not compatible with the new DSL. With the new DSL on, the legacy BaseExtension and the old variant API, such as applicationVariants, are removed. Google also lists changed defaults for other android.* properties, including android.useAndroidx, android.uniquePackageNames and android.r8.strictFullModeForKeepRules. Check the full list in the notes if you set any of them.

The error you will see

Flutter's issue #181383 shows this output from a plugin (camera_android_camerax 0.6.27) that still applies the Kotlin plugin under AGP 9.0. The first line and the explanation read:

Failed to apply plugin 'kotlin-android'.

The 'org.jetbrains.kotlin.android' plugin is no longer required for Kotlin support since AGP 9.0.

The same issue shows Flutter's own message for your app's Gradle file, starting with "Starting AGP 9+, the default has become built-in Kotlin. This results in a build failure when applying the kotlin-android plugin at" followed by the path of the file.

Flutter's docs say the same in plain terms: apps that use the kotlin-android plugin fail to build without migration.

Where Flutter stands

The tracking issue says Flutter found that all plugins in an Android project must also migrate to built-in Kotlin to avoid build failures. Because AGP 9 had already launched, Flutter says it advised developers against adopting AGP 9 until it could support all migration states. The issue was still open on October 18, 2026, with some work items unchecked.

The fix

These steps follow Flutter's guide for app developers. My advice: commit your work first, and change one thing at a time so you know which step fixed the build.

1. Upgrade Flutter

Use Flutter 3.44 or later. Flutter's docs say 3.44 added AGP 9 support with built-in Kotlin disabled. If you want to turn built-in Kotlin on, you need 3.47 or later.

2. Get the build working with the opt-out flags

Flutter's guide says the app should have these two flags in android/gradle.properties:

android.builtInKotlin=false
android.newDsl=false

Flutter's migrator adds them on the next flutter run or flutter build apk, or when you build from Android Studio. Add-to-app host apps must add both flags by hand to the host project's gradle.properties, because the migrator can't run during native host builds.

Issue #191703 is an add-to-app report on Flutter 3.47.1 with AGP 9.2.1 and Gradle 9.6.1. The reporter hit a NullPointerException in getLegacyAndroidExtension with the AGP 9 defaults, and says setting both flags to false fixed it. That issue was still open when I checked.

3. Migrate the app to built-in Kotlin

This applies only if your app already applies the Kotlin Gradle plugin, and only on Flutter 3.47 or later. If your app doesn't apply it, Flutter's guide says android.newDsl=false is all you need, so stop here. Do this step together with step 5, because with android.builtInKotlin=false the app still needs kotlin-android to compile Kotlin. On Flutter 3.44 to 3.46, stop after step 2. In android/app/build.gradle or build.gradle.kts, Flutter's guide says to remove the kotlin-android plugin and the kotlinOptions block, then add a kotlin block:

plugins {
    id("com.android.application")
    // ...
}

android {
    // ...
}

kotlin {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}

The guide has the same change for the older Groovy apply plugin syntax and for add-to-app host apps that use alias(libs.plugins.kotlin.android).

4. Check your plugins

Your plugins matter just as much as your own Gradle files. Flutter's guide says that if a build fails because a plugin has not migrated, you should check its changelog on pub.dev and file an issue titled "Migrate plugin to built-in Kotlin" with the plugin's authors. The guide links a separate migration guide for plugin authors.

5. Turn built-in Kotlin on

Once the app and its plugins are migrated, Flutter's guide says to set this in android/gradle.properties, on Flutter 3.47 or later, in the same change as step 3:

android.builtInKotlin=true

Then run flutter run or flutter build apk and confirm the app builds and launches.

About the AGP Upgrade Assistant

Android Studio has a tool under Tools > AGP Upgrade Assistant. Google says it translates build files for a newer AGP, checks AGP and Gradle compatibility, and checks third-party Gradle plugin versions. Google also says it relies on static analysis, doesn't support some setups such as Gradle Version Catalogs defined in settings files, and might still fail to perform a clean upgrade. In a Flutter project, my advice: use it on the android folder only as a starting point, and test with flutter build afterward.

If the build still fails after this

Flutter's docs say it will remove support for applying the Kotlin Gradle plugin in a future version, and later remove support for the old AGP DSL. Google's notes say the new DSL opt-out will be removed in AGP 10.0. So I'd treat the two false flags as a temporary bridge, not a fix.

If your error is about apply from: flutter.gradle, see the imperative apply fix. If it names the v1 embedding, see the v1 embedding guide. If Play Console flags page sizes after you update Android tooling, see the 16 KB guide.

Need a hand?

If your Flutter Android build still fails after the AGP upgrade, the App Fix Ticket covers it in two fixed-price steps. A $450 Diagnosis gives you the root cause with evidence and a fixed repair quote within 3 business days, credited toward the fix. If you go ahead, the $1,200 Fix takes 5 business days and comes as a pull request. Or send me a short description.