diff --git a/sdk/ai/azure-ai-agents/customizations/src/main/java/AgentsCustomizations.java b/sdk/ai/azure-ai-agents/customizations/src/main/java/AgentsCustomizations.java
index 5b80c6d17c8d9..ef6de02c3b1bc 100644
--- a/sdk/ai/azure-ai-agents/customizations/src/main/java/AgentsCustomizations.java
+++ b/sdk/ai/azure-ai-agents/customizations/src/main/java/AgentsCustomizations.java
@@ -147,22 +147,26 @@ private void protectPolymorphicBaseConstructors(LibraryCustomization customizati
         List<String> classNames = Arrays.asList("AgentHarness", "AgentOptimizationConfigurationBase",
             "AgentOptimizationEvaluationSet", "AgentOptimizationTargetCompletionDataSource",
             "AgentOptimizationTargetConfiguration", "AgentOptimizationUserConversationSimulationDataSource",
-            "CreateTelephonyBindingInput", "EvaluationVoiceModelConfiguration", "OptimizationContext",
-            "MemoryItem", "MemoryStoreDefinition",
-            "RealtimeAudioFormat", "RealtimeClientEvent", "RealtimeConversationItem",
-            "RealtimeConversationItemMessage", "RealtimeMcpError", "RealtimeSessionConfigurationBase",
-            "RealtimeTurnDetection", "TelephonyOutboundRetryPolicy", "TelephonyTransferDestination",
-            "UserConversationSimulationInterruptionConfiguration", "VoiceAgentGreetingConfiguration",
-            "VoiceAgentInterimResponseConfiguration", "VoiceAgentSystemTool", "VoiceAgentTool",
-            "VoiceAgentTurnDetectionConfiguration", "VoiceConversationEngine");
-
-        for (String className : classNames) {
-            ClassCustomization classCustomization = customization.getClass(MODELS_PACKAGE, className);
-            classCustomization.customizeAst(ast -> ast.getClassByName(className).ifPresent(clazz -> clazz
-                .getConstructors()
-                .stream()
-                .filter(constructor -> constructor.isPublic())
-                .forEach(constructor -> constructor.setModifiers(Modifier.Keyword.PROTECTED))));
+            "CreateTelephonyBindingInput", "TelephonyBinding", "TelephonyAddress", "EvaluationVoiceModelConfiguration",
+            "OptimizationContext", "MemoryItem", "MemoryStoreDefinition", "RealtimeAudioFormat", "RealtimeClientEvent",
+            "RealtimeConversationItem", "RealtimeConversationItemMessage", "RealtimeMcpError",
+            "RealtimeSessionConfigurationBase", "RealtimeTurnDetection", "TelephonyOutboundRetryPolicy",
+            "TelephonyTransferDestination", "UserConversationSimulationInterruptionConfiguration",
+            "VoiceAgentGreetingConfiguration", "VoiceAgentInterimResponseConfiguration", "VoiceAgentSystemTool",
+            "VoiceAgentTool", "VoiceAgentTurnDetectionConfiguration", "VoiceConversationEngine");
+
+        // TypeSpec can remove or replace a polymorphic root. Protect every root that is
+        // actually emitted, without requiring retired models to remain in the package.
+        for (ClassCustomization classCustomization : customization.getPackage(MODELS_PACKAGE).listClasses()) {
+            String className = classCustomization.getClassName();
+            if (!classNames.contains(className)) {
+                continue;
+            }
+            classCustomization.customizeAst(ast -> ast.getClassByName(className)
+                .ifPresent(clazz -> clazz.getConstructors()
+                    .stream()
+                    .filter(constructor -> constructor.isPublic())
+                    .forEach(constructor -> constructor.setModifiers(Modifier.Keyword.PROTECTED))));
         }
     }
 
diff --git a/sdk/ai/azure-ai-agents/src/test/java/com/azure/ai/agents/models/PolymorphicModelConstructorTests.java b/sdk/ai/azure-ai-agents/src/test/java/com/azure/ai/agents/models/PolymorphicModelConstructorTests.java
new file mode 100644
index 0000000000000..aa1ba18c2f754
--- /dev/null
+++ b/sdk/ai/azure-ai-agents/src/test/java/com/azure/ai/agents/models/PolymorphicModelConstructorTests.java
@@ -0,0 +1,71 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.ai.agents.models;
+
+import com.azure.ai.agents.BetaVoiceAgentsTelephonyClient;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.util.Arrays;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class PolymorphicModelConstructorTests {
+    @ParameterizedTest
+    @ValueSource(classes = { AgentHarness.class, TelephonyBinding.class, TelephonyOutboundRetryPolicy.class })
+    public void retainedRootsHaveProtectedConstructors(Class<?> modelClass) {
+        assertProtectedConstructors(modelClass);
+    }
+
+    @Test
+    public void bindingInputRootHasProtectedConstructors() {
+        Method createBinding = Arrays.stream(BetaVoiceAgentsTelephonyClient.class.getMethods())
+            .filter(method -> method.getName().equals("createTelephonyBinding")
+                && method.getParameterCount() == 2
+                && method.getParameterTypes()[0] == String.class)
+            .findFirst()
+            .orElseThrow(() -> new AssertionError("The typed createTelephonyBinding method must be present"));
+
+        assertEquals(TelephonyBinding.class, createBinding.getReturnType());
+        // Follow the generated API so both the legacy request root and its shared-model replacement are tested.
+        Class<?> inputClass = createBinding.getParameterTypes()[1];
+        assertTrue(
+            inputClass.getSimpleName().equals("CreateTelephonyBindingInput") || inputClass == TelephonyBinding.class,
+            inputClass.getName());
+        assertProtectedConstructors(inputClass);
+    }
+
+    @Test
+    public void transferDestinationRootHasProtectedConstructors() throws NoSuchMethodException {
+        // This is TelephonyTransferDestination before regeneration and TelephonyAddress afterwards.
+        Class<?> destinationClass = TelephonyTransferTarget.class.getMethod("getDestination").getReturnType();
+        assertTrue(destinationClass.getSimpleName().equals("TelephonyTransferDestination")
+            || destinationClass.getSimpleName().equals("TelephonyAddress"), destinationClass.getName());
+        assertProtectedConstructors(destinationClass);
+    }
+
+    @Test
+    public void unrelatedModelKeepsPublicConstructors() {
+        Constructor<?>[] constructors = TelephonyTransferTarget.class.getDeclaredConstructors();
+        assertTrue(constructors.length > 0);
+        for (Constructor<?> constructor : constructors) {
+            assertTrue(Modifier.isPublic(constructor.getModifiers()), constructor.toString());
+        }
+    }
+
+    private static void assertProtectedConstructors(Class<?> modelClass) {
+        assertTrue(Modifier.isPublic(modelClass.getModifiers()), modelClass.getName());
+        assertFalse(Modifier.isAbstract(modelClass.getModifiers()), modelClass.getName());
+        Constructor<?>[] constructors = modelClass.getDeclaredConstructors();
+        assertTrue(constructors.length > 0, modelClass.getName());
+        for (Constructor<?> constructor : constructors) {
+            assertTrue(Modifier.isProtected(constructor.getModifiers()), constructor.toString());
+        }
+    }
+}