diff --git a/firebaseai/ChatSample/Screens/ConversationScreen.swift b/firebaseai/ChatSample/Screens/ConversationScreen.swift
index 8d7c3c1a8..0b845efd1 100644
--- a/firebaseai/ChatSample/Screens/ConversationScreen.swift
+++ b/firebaseai/ChatSample/Screens/ConversationScreen.swift
@@ -17,12 +17,18 @@ import GenerativeAIUIComponents
 import SwiftUI
 
 struct ConversationScreen: View {
-  @EnvironmentObject
-  var viewModel: ConversationViewModel
+  let firebaseService: FirebaseAI
+  @StateObject var viewModel: ConversationViewModel
 
   @State
   private var userPrompt = ""
 
+  init(firebaseService: FirebaseAI) {
+    self.firebaseService = firebaseService
+    _viewModel =
+      StateObject(wrappedValue: ConversationViewModel(firebaseService: firebaseService))
+  }
+
   enum FocusedField: Hashable {
     case message
   }
@@ -110,11 +116,11 @@ struct ConversationScreen: View {
 
 struct ConversationScreen_Previews: PreviewProvider {
   struct ContainerView: View {
-    @StateObject var viewModel = ConversationViewModel()
+    @StateObject var viewModel = ConversationViewModel(firebaseService: FirebaseAI
+      .firebaseAI()) // Example service init
 
     var body: some View {
-      ConversationScreen()
-        .environmentObject(viewModel)
+      ConversationScreen(firebaseService: FirebaseAI.firebaseAI())
         .onAppear {
           viewModel.messages = ChatMessage.samples
         }
@@ -123,7 +129,7 @@ struct ConversationScreen_Previews: PreviewProvider {
 
   static var previews: some View {
     NavigationStack {
-      ConversationScreen()
+      ConversationScreen(firebaseService: FirebaseAI.firebaseAI())
     }
   }
 }
diff --git a/firebaseai/ChatSample/ViewModels/ConversationViewModel.swift b/firebaseai/ChatSample/ViewModels/ConversationViewModel.swift
index 1f77b8ff9..29cc06db4 100644
--- a/firebaseai/ChatSample/ViewModels/ConversationViewModel.swift
+++ b/firebaseai/ChatSample/ViewModels/ConversationViewModel.swift
@@ -35,10 +35,8 @@ class ConversationViewModel: ObservableObject {
 
   private var chatTask: Task<Void, Never>?
 
-  init() {
-    // model = FirebaseAI.firebaseAI(backend: .vertexAI()).generativeModel(modelName: "gemini-2.0-flash-001")
-    model = FirebaseAI.firebaseAI(backend: .googleAI())
-      .generativeModel(modelName: "gemini-2.0-flash-001")
+  init(firebaseService: FirebaseAI) {
+    model = firebaseService.generativeModel(modelName: "gemini-2.0-flash-001")
     chat = model.startChat()
   }
 
diff --git a/firebaseai/FirebaseAISample/ContentView.swift b/firebaseai/FirebaseAISample/ContentView.swift
index 2c13af833..af7f2035f 100644
--- a/firebaseai/FirebaseAISample/ContentView.swift
+++ b/firebaseai/FirebaseAISample/ContentView.swift
@@ -13,45 +13,72 @@
 // limitations under the License.
 
 import SwiftUI
+import FirebaseAI
 
-struct ContentView: View {
-  @StateObject
-  var viewModel = ConversationViewModel()
+enum BackendOption: String, CaseIterable, Identifiable {
+  case googleAI = "Google AI"
+  case vertexAI = "Vertex AI"
+  var id: String { rawValue }
+
+  var backendValue: FirebaseAI {
+    switch self {
+    case .googleAI:
+      return FirebaseAI.firebaseAI(backend: .googleAI())
+    case .vertexAI:
+      return FirebaseAI.firebaseAI(backend: .vertexAI())
+    }
+  }
+}
 
-  @StateObject
-  var functionCallingViewModel = FunctionCallingViewModel()
+struct ContentView: View {
+  @State private var selectedBackend: BackendOption = .googleAI
+  @State private var firebaseService: FirebaseAI = FirebaseAI.firebaseAI(backend: .googleAI())
 
   var body: some View {
     NavigationStack {
       List {
-        NavigationLink {
-          SummarizeScreen()
-        } label: {
-          Label("Text", systemImage: "doc.text")
+        Section("Configuration") {
+          Picker("Backend", selection: $selectedBackend) {
+            ForEach(BackendOption.allCases) { option in
+              Text(option.rawValue).tag(option)
+            }
+          }
         }
-        NavigationLink {
-          PhotoReasoningScreen()
-        } label: {
-          Label("Multi-modal", systemImage: "doc.richtext")
-        }
-        NavigationLink {
-          ConversationScreen()
-            .environmentObject(viewModel)
-        } label: {
-          Label("Chat", systemImage: "ellipsis.message.fill")
-        }
-        NavigationLink {
-          FunctionCallingScreen().environmentObject(functionCallingViewModel)
-        } label: {
-          Label("Function Calling", systemImage: "function")
-        }
-        NavigationLink {
-          ImagenScreen()
-        } label: {
-          Label("Imagen", systemImage: "camera.circle")
+
+        Section("Samples") {
+          NavigationLink {
+            SummarizeScreen(firebaseService: firebaseService)
+          } label: {
+            Label("Text", systemImage: "doc.text")
+          }
+          NavigationLink {
+            PhotoReasoningScreen(firebaseService: firebaseService)
+          } label: {
+            Label("Multi-modal", systemImage: "doc.richtext")
+          }
+          NavigationLink {
+            ConversationScreen(firebaseService: firebaseService)
+          } label: {
+            Label("Chat", systemImage: "ellipsis.message.fill")
+          }
+          NavigationLink {
+            FunctionCallingScreen(firebaseService: firebaseService)
+          } label: {
+            Label("Function Calling", systemImage: "function")
+          }
+          NavigationLink {
+            ImagenScreen(firebaseService: firebaseService)
+          } label: {
+            Label("Imagen", systemImage: "camera.circle")
+          }
         }
       }
       .navigationTitle("Generative AI Samples")
+      .onChange(of: selectedBackend) { newBackend in
+        firebaseService = newBackend.backendValue
+        // Note: This might cause views that hold the old service instance to misbehave
+        // unless they are also correctly updated or recreated.
+      }
     }
   }
 }
diff --git a/firebaseai/FunctionCallingSample/Screens/FunctionCallingScreen.swift b/firebaseai/FunctionCallingSample/Screens/FunctionCallingScreen.swift
index 71de0c2cf..474a55ede 100644
--- a/firebaseai/FunctionCallingSample/Screens/FunctionCallingScreen.swift
+++ b/firebaseai/FunctionCallingSample/Screens/FunctionCallingScreen.swift
@@ -17,12 +17,18 @@ import GenerativeAIUIComponents
 import SwiftUI
 
 struct FunctionCallingScreen: View {
-  @EnvironmentObject
-  var viewModel: FunctionCallingViewModel
+  let firebaseService: FirebaseAI
+  @StateObject var viewModel: FunctionCallingViewModel
 
   @State
   private var userPrompt = "What is 100 Euros in U.S. Dollars?"
 
+  init(firebaseService: FirebaseAI) {
+    self.firebaseService = firebaseService
+    _viewModel =
+      StateObject(wrappedValue: FunctionCallingViewModel(firebaseService: firebaseService))
+  }
+
   enum FocusedField: Hashable {
     case message
   }
@@ -112,11 +118,10 @@ struct FunctionCallingScreen: View {
 
 struct FunctionCallingScreen_Previews: PreviewProvider {
   struct ContainerView: View {
-    @EnvironmentObject
-    var viewModel: FunctionCallingViewModel
+    @StateObject var viewModel = FunctionCallingViewModel(firebaseService: FirebaseAI.firebaseAI())
 
     var body: some View {
-      FunctionCallingScreen()
+      FunctionCallingScreen(firebaseService: FirebaseAI.firebaseAI())
         .onAppear {
           viewModel.messages = ChatMessage.samples
         }
@@ -125,7 +130,7 @@ struct FunctionCallingScreen_Previews: PreviewProvider {
 
   static var previews: some View {
     NavigationStack {
-      FunctionCallingScreen().environmentObject(FunctionCallingViewModel())
+      FunctionCallingScreen(firebaseService: FirebaseAI.firebaseAI())
     }
   }
 }
diff --git a/firebaseai/FunctionCallingSample/ViewModels/FunctionCallingViewModel.swift b/firebaseai/FunctionCallingSample/ViewModels/FunctionCallingViewModel.swift
index 2c04c6a6d..8bd7f90ef 100644
--- a/firebaseai/FunctionCallingSample/ViewModels/FunctionCallingViewModel.swift
+++ b/firebaseai/FunctionCallingSample/ViewModels/FunctionCallingViewModel.swift
@@ -37,12 +37,11 @@ class FunctionCallingViewModel: ObservableObject {
 
   private var chatTask: Task<Void, Never>?
 
-  init() {
-    // model = FirebaseAI.firebaseAI(backend: .vertexAI()).generativeModel(
-    model = FirebaseAI.firebaseAI(backend: .googleAI()).generativeModel(
-      modelName: "gemini-2.0-flash-001",
-      tools: [.functionDeclarations([
-        FunctionDeclaration(
+  init(firebaseService: FirebaseAI) { // Accept FirebaseAI instance
+      model = firebaseService.generativeModel(
+          modelName: "gemini-2.0-flash-001",
+          tools: [.functionDeclarations([
+              FunctionDeclaration(
           name: "get_exchange_rate",
           description: "Get the exchange rate for currencies between countries",
           parameters: [
@@ -57,8 +56,8 @@ class FunctionCallingViewModel: ObservableObject {
           ]
         ),
       ])]
-    )
-    chat = model.startChat()
+      )
+      chat = model.startChat() // Initialize chat with the model from the service
   }
 
   func sendMessage(_ text: String, streaming: Bool = true) async {
diff --git a/firebaseai/GenerativeAIMultimodalSample/Screens/PhotoReasoningScreen.swift b/firebaseai/GenerativeAIMultimodalSample/Screens/PhotoReasoningScreen.swift
index 930214770..e3796f387 100644
--- a/firebaseai/GenerativeAIMultimodalSample/Screens/PhotoReasoningScreen.swift
+++ b/firebaseai/GenerativeAIMultimodalSample/Screens/PhotoReasoningScreen.swift
@@ -16,9 +16,17 @@ import GenerativeAIUIComponents
 import MarkdownUI
 import PhotosUI
 import SwiftUI
+import FirebaseAI
 
 struct PhotoReasoningScreen: View {
-  @StateObject var viewModel = PhotoReasoningViewModel()
+  let firebaseService: FirebaseAI
+  @StateObject var viewModel: PhotoReasoningViewModel
+
+  init(firebaseService: FirebaseAI) {
+    self.firebaseService = firebaseService
+    _viewModel =
+      StateObject(wrappedValue: PhotoReasoningViewModel(firebaseService: firebaseService))
+  }
 
   enum FocusedField: Hashable {
     case message
@@ -73,6 +81,6 @@ struct PhotoReasoningScreen: View {
 
 #Preview {
   NavigationStack {
-    PhotoReasoningScreen()
+    PhotoReasoningScreen(firebaseService: FirebaseAI.firebaseAI())
   }
 }
diff --git a/firebaseai/GenerativeAIMultimodalSample/ViewModels/PhotoReasoningViewModel.swift b/firebaseai/GenerativeAIMultimodalSample/ViewModels/PhotoReasoningViewModel.swift
index b64d167b9..24a2e96e2 100644
--- a/firebaseai/GenerativeAIMultimodalSample/ViewModels/PhotoReasoningViewModel.swift
+++ b/firebaseai/GenerativeAIMultimodalSample/ViewModels/PhotoReasoningViewModel.swift
@@ -43,10 +43,8 @@ class PhotoReasoningViewModel: ObservableObject {
 
   private var model: GenerativeModel?
 
-  init() {
-    // model = FirebaseAI.firebaseAI(backend: .vertexAI()).generativeModel(modelName: "gemini-2.0-flash-001")
-    model = FirebaseAI.firebaseAI(backend: .googleAI())
-      .generativeModel(modelName: "gemini-2.0-flash-001")
+  init(firebaseService: FirebaseAI) {
+    model = firebaseService.generativeModel(modelName: "gemini-2.0-flash-001")
   }
 
   func reason() async {
diff --git a/firebaseai/GenerativeAITextSample/Screens/SummarizeScreen.swift b/firebaseai/GenerativeAITextSample/Screens/SummarizeScreen.swift
index 748c1addd..f11bcafc5 100644
--- a/firebaseai/GenerativeAITextSample/Screens/SummarizeScreen.swift
+++ b/firebaseai/GenerativeAITextSample/Screens/SummarizeScreen.swift
@@ -14,11 +14,18 @@
 
 import MarkdownUI
 import SwiftUI
+import FirebaseAI
 
 struct SummarizeScreen: View {
-  @StateObject var viewModel = SummarizeViewModel()
+  let firebaseService: FirebaseAI
+  @StateObject var viewModel: SummarizeViewModel
   @State var userInput = ""
 
+  init(firebaseService: FirebaseAI) {
+    self.firebaseService = firebaseService
+    _viewModel = StateObject(wrappedValue: SummarizeViewModel(firebaseService: firebaseService))
+  }
+
   enum FocusedField: Hashable {
     case message
   }
@@ -75,6 +82,6 @@ struct SummarizeScreen: View {
 
 #Preview {
   NavigationStack {
-    SummarizeScreen()
+    SummarizeScreen(firebaseService: FirebaseAI.firebaseAI())
   }
 }
diff --git a/firebaseai/GenerativeAITextSample/ViewModels/SummarizeViewModel.swift b/firebaseai/GenerativeAITextSample/ViewModels/SummarizeViewModel.swift
index 512ee1c80..94c41e70a 100644
--- a/firebaseai/GenerativeAITextSample/ViewModels/SummarizeViewModel.swift
+++ b/firebaseai/GenerativeAITextSample/ViewModels/SummarizeViewModel.swift
@@ -31,10 +31,8 @@ class SummarizeViewModel: ObservableObject {
 
   private var model: GenerativeModel?
 
-  init() {
-    // model = FirebaseAI.firebaseAI(backend: .vertexAI()).generativeModel(modelName: "gemini-2.0-flash-001")
-    model = FirebaseAI.firebaseAI(backend: .googleAI())
-      .generativeModel(modelName: "gemini-2.0-flash-001")
+  init(firebaseService: FirebaseAI) {
+    model = firebaseService.generativeModel(modelName: "gemini-2.0-flash-001")
   }
 
   func summarize(inputText: String) async {
diff --git a/firebaseai/ImagenScreen/ImagenScreen.swift b/firebaseai/ImagenScreen/ImagenScreen.swift
index 3d621bb41..e961fef56 100644
--- a/firebaseai/ImagenScreen/ImagenScreen.swift
+++ b/firebaseai/ImagenScreen/ImagenScreen.swift
@@ -14,9 +14,16 @@
 
 import SwiftUI
 import GenerativeAIUIComponents
+import FirebaseAI
 
 struct ImagenScreen: View {
-  @StateObject var viewModel = ImagenViewModel()
+  let firebaseService: FirebaseAI
+  @StateObject var viewModel: ImagenViewModel
+
+  init(firebaseService: FirebaseAI) {
+    self.firebaseService = firebaseService
+    _viewModel = StateObject(wrappedValue: ImagenViewModel(firebaseService: firebaseService))
+  }
 
   enum FocusedField: Hashable {
     case message
@@ -103,5 +110,5 @@ struct ProgressOverlay: View {
 }
 
 #Preview {
-  ImagenScreen()
+  ImagenScreen(firebaseService: FirebaseAI.firebaseAI())
 }
diff --git a/firebaseai/ImagenScreen/ImagenViewModel.swift b/firebaseai/ImagenScreen/ImagenViewModel.swift
index 3997ce156..d4fc2b43f 100644
--- a/firebaseai/ImagenScreen/ImagenViewModel.swift
+++ b/firebaseai/ImagenScreen/ImagenViewModel.swift
@@ -37,11 +37,7 @@ class ImagenViewModel: ObservableObject {
 
   private var generateImagesTask: Task<Void, Never>?
 
-  // 1. Initialize the Gemini service
-  // private let service = FirebaseAI.firebaseAI(backend: .vertexAI())
-  private let service = FirebaseAI.firebaseAI(backend: .googleAI())
-  init() {
-    // 2. Configure Imagen settings
+  init(firebaseService: FirebaseAI) {
     let modelName = "imagen-3.0-generate-002"
     let safetySettings = ImagenSafetySettings(
       safetyFilterLevel: .blockLowAndAbove
@@ -50,8 +46,7 @@ class ImagenViewModel: ObservableObject {
     generationConfig.numberOfImages = 4
     generationConfig.aspectRatio = .landscape4x3
 
-    // 3. Initialize the Imagen model
-    model = service.imagenModel(
+    model = firebaseService.imagenModel(
       modelName: modelName,
       generationConfig: generationConfig,
       safetySettings: safetySettings