diff --git a/.github/workflows/android.yml b/.github/workflows/android.yml
index c4aef066..8110f61a 100644
--- a/.github/workflows/android.yml
+++ b/.github/workflows/android.yml
@@ -29,11 +29,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: '17'
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
@@ -88,11 +88,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: '17'
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
@@ -125,11 +125,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: '17'
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
@@ -163,11 +163,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: '17'
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
@@ -205,11 +205,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: '17'
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
@@ -236,11 +236,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: '17'
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 97b70c7e..b9093921 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -27,11 +27,11 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: "17"
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
@@ -78,11 +78,11 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: "17"
+          java-version: '21'
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v6
diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index d6328b64..612b7bf3 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -75,8 +75,8 @@ android {
         }
     }
     compileOptions {
-        sourceCompatibility = JavaVersion.VERSION_17
-        targetCompatibility = JavaVersion.VERSION_17
+        sourceCompatibility = JavaVersion.VERSION_21
+        targetCompatibility = JavaVersion.VERSION_21
     }
     buildFeatures {
         compose = true
@@ -99,7 +99,7 @@ android {
 }
 
 kotlin {
-    jvmToolchain(17)
+    jvmToolchain(21)
 }
 
 room {
diff --git a/flake.nix b/flake.nix
index e680eb64..2602cb86 100644
--- a/flake.nix
+++ b/flake.nix
@@ -56,8 +56,8 @@
       in {
         devShells.default = pkgs.mkShell {
           buildInputs = with pkgs; [
-            # Java 17 (required for AGP 8.x / Gradle 8.x)
-            jdk17
+            # Java 21 (required for AGP 9.x / Gradle 9.x)
+            jdk21
 
             # Android SDK (platforms, build-tools, platform-tools)
             androidSdk
@@ -75,7 +75,7 @@
           # Point everything at the Nix-managed SDK
           ANDROID_HOME = "${androidSdk}/libexec/android-sdk";
           ANDROID_SDK_ROOT = "${androidSdk}/libexec/android-sdk";
-          JAVA_HOME = "${pkgs.jdk17}";
+          JAVA_HOME = "${pkgs.jdk21}";
 
           # Gradle needs a writable home
           GRADLE_USER_HOME = "$PWD/.gradle-home";