diff --git a/firebase-installations/api.txt b/firebase-installations/api.txt
index 4e5eb23d352..2024c519fd0 100644
--- a/firebase-installations/api.txt
+++ b/firebase-installations/api.txt
@@ -93,7 +93,7 @@ package com.google.firebase.installations.remote {
 
   public class FirebaseInstallationServiceClient {
     ctor public FirebaseInstallationServiceClient(@NonNull android.content.Context, @Nullable com.google.firebase.platforminfo.UserAgentPublisher, @Nullable com.google.firebase.heartbeatinfo.HeartBeatInfo);
-    method @NonNull public com.google.firebase.installations.remote.InstallationResponse createFirebaseInstallation(@NonNull String, @NonNull String, @NonNull String, @NonNull String) throws java.io.IOException;
+    method @NonNull public com.google.firebase.installations.remote.InstallationResponse createFirebaseInstallation(@NonNull String, @NonNull String, @NonNull String, @NonNull String, @Nullable String) throws java.io.IOException;
     method @NonNull public void deleteFirebaseInstallation(@NonNull String, @NonNull String, @NonNull String, @NonNull String) throws com.google.firebase.FirebaseException, java.io.IOException;
     method @NonNull public com.google.firebase.installations.remote.TokenResult generateAuthToken(@NonNull String, @NonNull String, @NonNull String, @NonNull String) throws java.io.IOException;
   }
diff --git a/firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java b/firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java
index 7abd5351ed7..8288d2c205f 100644
--- a/firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java
+++ b/firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java
@@ -307,8 +307,8 @@ private final void doRegistrationInternal(boolean forceRefresh) {
    *     been persisted.
    */
   private PersistedInstallationEntry getPrefsWithGeneratedIdMultiProcessSafe() {
-    CrossProcessLock lock = CrossProcessLock
-        .acquire(firebaseApp.getApplicationContext(), LOCKFILE_NAME_GENERATE_FID);
+    CrossProcessLock lock =
+        CrossProcessLock.acquire(firebaseApp.getApplicationContext(), LOCKFILE_NAME_GENERATE_FID);
     try {
       synchronized (lockGenerateFid) {
         PersistedInstallationEntry prefs =
@@ -354,7 +354,8 @@ private PersistedInstallationEntry registerFidWithServer(PersistedInstallationEn
             /*apiKey= */ firebaseApp.getOptions().getApiKey(),
             /*fid= */ prefs.getFirebaseInstallationId(),
             /*projectID= */ firebaseApp.getOptions().getProjectId(),
-            /*appId= */ getApplicationId());
+            /*appId= */ getApplicationId(),
+            /* migration-header= */ null);
 
     switch (response.getResponseCode()) {
       case OK:
diff --git a/firebase-installations/src/main/java/com/google/firebase/installations/remote/FirebaseInstallationServiceClient.java b/firebase-installations/src/main/java/com/google/firebase/installations/remote/FirebaseInstallationServiceClient.java
index bb392f9472e..a92dd0ba922 100644
--- a/firebase-installations/src/main/java/com/google/firebase/installations/remote/FirebaseInstallationServiceClient.java
+++ b/firebase-installations/src/main/java/com/google/firebase/installations/remote/FirebaseInstallationServiceClient.java
@@ -70,6 +70,8 @@ public class FirebaseInstallationServiceClient {
   private static final String X_ANDROID_PACKAGE_HEADER_KEY = "X-Android-Package";
   private static final String X_ANDROID_CERT_HEADER_KEY = "X-Android-Cert";
 
+  private static final String X_ANDROID_IID_MIGRATION_KEY = "x-goog-fis-android-iid-migration-auth";
+
   private static final int NETWORK_TIMEOUT_MILLIS = 10000;
 
   private static final Pattern EXPIRATION_TIMESTAMP_PATTERN = Pattern.compile("[0-9]+s");
@@ -87,10 +89,10 @@ public class FirebaseInstallationServiceClient {
   public FirebaseInstallationServiceClient(
       @NonNull Context context,
       @Nullable UserAgentPublisher publisher,
-      @Nullable HeartBeatInfo heartBeatInfo) {
+      @Nullable HeartBeatInfo heartbeatInfo) {
     this.context = context;
     this.userAgentPublisher = publisher;
-    this.heartbeatInfo = heartBeatInfo;
+    this.heartbeatInfo = heartbeatInfo;
   }
 
   /**
@@ -100,6 +102,8 @@ public FirebaseInstallationServiceClient(
    * @param fid Firebase Installation Identifier
    * @param projectID Project Id
    * @param appId the identifier of a Firebase application
+   * @param iidToken the identifier token of a Firebase application with instance id. It is set to
+   *     null for a FID.
    * @return {@link InstallationResponse} generated from the response body
    *     <ul>
    *       <li>400: return response with status BAD_CONFIG
@@ -111,7 +115,11 @@ public FirebaseInstallationServiceClient(
    */
   @NonNull
   public InstallationResponse createFirebaseInstallation(
-      @NonNull String apiKey, @NonNull String fid, @NonNull String projectID, @NonNull String appId)
+      @NonNull String apiKey,
+      @NonNull String fid,
+      @NonNull String projectID,
+      @NonNull String appId,
+      @Nullable String iidToken)
       throws IOException {
     String resourceName = String.format(CREATE_REQUEST_RESOURCE_NAME_FORMAT, projectID);
     int retryCount = 0;
@@ -128,6 +136,11 @@ public InstallationResponse createFirebaseInstallation(
       httpsURLConnection.setRequestMethod("POST");
       httpsURLConnection.setDoOutput(true);
 
+      // Note: Set the iid token header for authenticating the Instance-ID migrating to FIS.
+      if (iidToken != null) {
+        httpsURLConnection.addRequestProperty(X_ANDROID_IID_MIGRATION_KEY, iidToken);
+      }
+
       GZIPOutputStream gzipOutputStream =
           new GZIPOutputStream(httpsURLConnection.getOutputStream());
       try {
diff --git a/firebase-installations/src/test/java/com/google/firebase/installations/FirebaseInstallationsTest.java b/firebase-installations/src/test/java/com/google/firebase/installations/FirebaseInstallationsTest.java
index 5dc10b77fda..9cabfa99494 100644
--- a/firebase-installations/src/test/java/com/google/firebase/installations/FirebaseInstallationsTest.java
+++ b/firebase-installations/src/test/java/com/google/firebase/installations/FirebaseInstallationsTest.java
@@ -20,6 +20,7 @@
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.matches;
 import static org.mockito.Mockito.doAnswer;
@@ -178,7 +179,8 @@ public void cleanUp() {
    */
   @Test
   public void testGetId_noNetwork_noIid() throws Exception {
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenThrow(new IOException());
     when(mockBackend.generateAuthToken(anyString(), anyString(), anyString(), anyString()))
         .thenThrow(new IOException());
@@ -207,7 +209,8 @@ public void testGetId_noNetwork_noIid() throws Exception {
 
   @Test
   public void testGetId_noNetwork_iidPresent() throws Exception {
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenThrow(new IOException());
     when(mockBackend.generateAuthToken(anyString(), anyString(), anyString(), anyString()))
         .thenThrow(new IOException());
@@ -236,7 +239,8 @@ public void testGetId_noNetwork_iidPresent() throws Exception {
 
   @Test
   public void testGetId_noNetwork_fidAlreadyGenerated() throws Exception {
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenThrow(new IOException());
     when(mockBackend.generateAuthToken(anyString(), anyString(), anyString(), anyString()))
         .thenThrow(new IOException());
@@ -303,7 +307,7 @@ public void testGetId_ValidIdAndToken_NoBackendCalls() throws Exception {
   @Test
   public void testGetId_UnRegisteredId_IssueCreateIdCall() throws Exception {
     when(mockBackend.createFirebaseInstallation(
-            anyString(), matches(TEST_FID_1), anyString(), anyString()))
+            anyString(), matches(TEST_FID_1), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE);
     persistedInstallation.insertOrUpdatePersistedInstallationEntry(
         PersistedInstallationEntry.INSTANCE.withUnregisteredFid(TEST_FID_1));
@@ -322,7 +326,8 @@ public void testGetId_UnRegisteredId_IssueCreateIdCall() throws Exception {
     // check that the mockClient didn't get invoked at all, since the fid is already registered
     // and the authtoken is present and not expired
     verify(mockBackend)
-        .createFirebaseInstallation(anyString(), matches(TEST_FID_1), anyString(), anyString());
+        .createFirebaseInstallation(
+            anyString(), matches(TEST_FID_1), anyString(), anyString(), any());
     verify(mockBackend, never())
         .generateAuthToken(anyString(), anyString(), anyString(), anyString());
 
@@ -335,7 +340,8 @@ public void testGetId_UnRegisteredId_IssueCreateIdCall() throws Exception {
   @Test
   public void testGetId_migrateIid_successful() throws Exception {
     when(mockIidStore.readIid()).thenReturn(TEST_INSTANCE_ID_1);
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE_WITH_IID);
 
     // Do the actual getId() call under test.
@@ -361,7 +367,8 @@ public void testGetId_migrateIid_successful() throws Exception {
   @Test
   public void testGetId_multipleCalls_sameFIDReturned() throws Exception {
     when(mockIidStore.readIid()).thenReturn(null);
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE);
 
     // Call getId multiple times
@@ -384,7 +391,7 @@ public void testGetId_multipleCalls_sameFIDReturned() throws Exception {
         .that(task2.getResult())
         .isEqualTo(TEST_FID_1);
     verify(mockBackend, times(1))
-        .createFirebaseInstallation(TEST_API_KEY, TEST_FID_1, TEST_PROJECT_ID, TEST_APP_ID_1);
+        .createFirebaseInstallation(TEST_API_KEY, TEST_FID_1, TEST_PROJECT_ID, TEST_APP_ID_1, null);
     PersistedInstallationEntry entry = persistedInstallation.readPersistedInstallationEntryValue();
     assertThat(entry.getFirebaseInstallationId(), equalTo(TEST_FID_1));
     assertTrue("the entry isn't doesn't have a registered fid: " + entry, entry.isRegistered());
@@ -399,7 +406,8 @@ public void testGetId_unregistered_replacesFidWithResponse() throws Exception {
     // Update local storage with installation entry that has invalid fid.
     persistedInstallation.insertOrUpdatePersistedInstallationEntry(
         PersistedInstallationEntry.INSTANCE.withUnregisteredFid("tobereplaced"));
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE);
 
     // The first call will return the existing FID, "tobereplaced"
@@ -435,7 +443,8 @@ public void testGetId_ServerError_UnregisteredFID() throws Exception {
         PersistedInstallationEntry.INSTANCE.withUnregisteredFid(TEST_FID_1));
 
     // have the server return a server error for the registration
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(
             InstallationResponse.builder().setResponseCode(ResponseCode.BAD_CONFIG).build());
 
@@ -469,7 +478,8 @@ public void testGetId_fidRegistrationUncheckedException_statusUpdated() throws E
         PersistedInstallationEntry.INSTANCE.withUnregisteredFid(TEST_FID_1));
 
     // Mocking unchecked exception on FIS createFirebaseInstallation
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenThrow(new IOException());
 
     TestOnCompleteListener<String> onCompleteListener = new TestOnCompleteListener<>();
@@ -569,14 +579,15 @@ public void testGetId_expiredAuthToken_refreshesAuthToken() throws Exception {
         .isEqualTo(TEST_AUTH_TOKEN_2);
 
     verify(mockBackend, never())
-        .createFirebaseInstallation(TEST_API_KEY, TEST_FID_1, TEST_PROJECT_ID, TEST_APP_ID_1);
+        .createFirebaseInstallation(TEST_API_KEY, TEST_FID_1, TEST_PROJECT_ID, TEST_APP_ID_1, null);
     verify(mockBackend, times(1))
         .generateAuthToken(TEST_API_KEY, TEST_FID_1, TEST_PROJECT_ID, TEST_REFRESH_TOKEN);
   }
 
   @Test
   public void testGetAuthToken_fidDoesNotExist_successful() throws Exception {
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE);
 
     TestOnCompleteListener<InstallationTokenResult> onCompleteListener =
@@ -650,7 +661,8 @@ public void testGetToken_unregisteredFid_fetchedNewTokenFromFIS() throws Excepti
     // calls getId to ensure FID registration and returns a valid auth token.
     persistedInstallation.insertOrUpdatePersistedInstallationEntry(
         PersistedInstallationEntry.INSTANCE.withUnregisteredFid(TEST_FID_1));
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE);
 
     TestOnCompleteListener<InstallationTokenResult> onCompleteListener =
@@ -859,7 +871,8 @@ public void testDelete_registeredFID_successful() throws Exception {
             utils.currentTimeInSecs(),
             TEST_AUTH_TOKEN,
             TEST_TOKEN_EXPIRATION_TIMESTAMP));
-    when(mockBackend.createFirebaseInstallation(anyString(), anyString(), anyString(), anyString()))
+    when(mockBackend.createFirebaseInstallation(
+            anyString(), anyString(), anyString(), anyString(), any()))
         .thenReturn(TEST_INSTALLATION_RESPONSE);
 
     TestOnCompleteListener<Void> onCompleteListener = new TestOnCompleteListener<>();