diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
index c552c772b..bf7bb7f7a 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
@@ -767,7 +767,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
             config.getCdnConfiguration().getBucket()),
         new VerificationController(registrationServiceClient, new VerificationSessionManager(verificationSessions),
             pushNotificationManager, registrationCaptchaManager, registrationRecoveryPasswordsManager, rateLimiters,
-            clock)
+            accountsManager, clock)
     );
     if (config.getSubscription() != null && config.getOneTimeDonations() != null) {
       commonControllers.add(new SubscriptionController(clock, config.getSubscription(), config.getOneTimeDonations(),
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountController.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountController.java
index c593f093e..50c6f0ba2 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountController.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountController.java
@@ -238,7 +238,7 @@ public class AccountController {
           storedVerificationCode = existingStoredVerificationCode;
         }
       } else {
-        final byte[] sessionId = createRegistrationSession(phoneNumber);
+        final byte[] sessionId = createRegistrationSession(phoneNumber, accounts.getByE164(number).isPresent());
         storedVerificationCode = new StoredVerificationCode(null, clock.millis(), generatePushChallenge(), sessionId);
         new StoredVerificationCode(null, clock.millis(), generatePushChallenge(), sessionId);
       }
@@ -345,8 +345,9 @@ public class AccountController {
 
     // During the transition to explicit session creation, some previously-stored records may not have a session ID;
     // after the transition, we can assume that any existing record has an associated session ID.
-    final byte[] sessionId =  maybeStoredVerificationCode.isPresent() && maybeStoredVerificationCode.get().sessionId() != null ?
-        maybeStoredVerificationCode.get().sessionId() : createRegistrationSession(phoneNumber);
+    final byte[] sessionId =  maybeStoredVerificationCode.isPresent() && maybeStoredVerificationCode.get().sessionId() != null
+        ? maybeStoredVerificationCode.get().sessionId()
+        : createRegistrationSession(phoneNumber, accounts.getByE164(number).isPresent());
 
     sendVerificationCode(sessionId, messageTransport, clientType, acceptLanguage);
 
@@ -859,10 +860,11 @@ public class AccountController {
     return HexFormat.of().formatHex(challenge);
   }
 
-  private byte[] createRegistrationSession(final Phonenumber.PhoneNumber phoneNumber) throws RateLimitExceededException {
+  private byte[] createRegistrationSession(final Phonenumber.PhoneNumber phoneNumber,
+      final boolean accountExistsWithPhoneNumber) throws RateLimitExceededException {
 
     try {
-      return registrationServiceClient.createRegistrationSession(phoneNumber, REGISTRATION_RPC_TIMEOUT).join();
+      return registrationServiceClient.createRegistrationSession(phoneNumber, accountExistsWithPhoneNumber, REGISTRATION_RPC_TIMEOUT).join();
     } catch (final CompletionException e) {
       rethrowRateLimitException(e);
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
index 074d73ef4..d7955e37a 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
@@ -76,6 +76,7 @@ import org.whispersystems.textsecuregcm.registration.RegistrationServiceExceptio
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceSenderException;
 import org.whispersystems.textsecuregcm.registration.VerificationSession;
 import org.whispersystems.textsecuregcm.spam.FilterSpam;
+import org.whispersystems.textsecuregcm.storage.AccountsManager;
 import org.whispersystems.textsecuregcm.storage.RegistrationRecoveryPasswordsManager;
 import org.whispersystems.textsecuregcm.storage.VerificationSessionManager;
 import org.whispersystems.textsecuregcm.util.ExceptionUtils;
@@ -112,6 +113,7 @@ public class VerificationController {
   private final RegistrationCaptchaManager registrationCaptchaManager;
   private final RegistrationRecoveryPasswordsManager registrationRecoveryPasswordsManager;
   private final RateLimiters rateLimiters;
+  private final AccountsManager accountsManager;
 
   private final Clock clock;
 
@@ -119,7 +121,9 @@ public class VerificationController {
       final VerificationSessionManager verificationSessionManager,
       final PushNotificationManager pushNotificationManager,
       final RegistrationCaptchaManager registrationCaptchaManager,
-      final RegistrationRecoveryPasswordsManager registrationRecoveryPasswordsManager, final RateLimiters rateLimiters,
+      final RegistrationRecoveryPasswordsManager registrationRecoveryPasswordsManager,
+      final RateLimiters rateLimiters,
+      final AccountsManager accountsManager,
       final Clock clock) {
     this.registrationServiceClient = registrationServiceClient;
     this.verificationSessionManager = verificationSessionManager;
@@ -127,6 +131,7 @@ public class VerificationController {
     this.registrationCaptchaManager = registrationCaptchaManager;
     this.registrationRecoveryPasswordsManager = registrationRecoveryPasswordsManager;
     this.rateLimiters = rateLimiters;
+    this.accountsManager = accountsManager;
     this.clock = clock;
   }
 
@@ -151,6 +156,7 @@ public class VerificationController {
     final RegistrationServiceSession registrationServiceSession;
     try {
       registrationServiceSession = registrationServiceClient.createRegistrationSessionSession(phoneNumber,
+          accountsManager.getByE164(request.getNumber()).isPresent(),
           REGISTRATION_RPC_TIMEOUT).join();
     } catch (final CancellationException e) {
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java b/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
index 779316bfc..89284f500 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
@@ -81,13 +81,14 @@ public class RegistrationServiceClient implements Managed {
   // The …Session suffix methods distinguish the new methods, which return Sessions, from the old.
   // Once the deprecated methods are removed, the names can be streamlined.
   public CompletableFuture<RegistrationServiceSession> createRegistrationSessionSession(
-      final Phonenumber.PhoneNumber phoneNumber, final Duration timeout) {
+      final Phonenumber.PhoneNumber phoneNumber, final boolean accountExistsWithPhoneNumber, final Duration timeout) {
     final long e164 = Long.parseLong(
         PhoneNumberUtil.getInstance().format(phoneNumber, PhoneNumberUtil.PhoneNumberFormat.E164).substring(1));
 
     return toCompletableFuture(stub.withDeadline(toDeadline(timeout))
         .createSession(CreateRegistrationSessionRequest.newBuilder()
             .setE164(e164)
+            .setAccountExistsWithE164(accountExistsWithPhoneNumber)
             .build()))
         .thenApply(response -> switch (response.getResponseCase()) {
           case SESSION_METADATA -> buildSessionResponseFromMetadata(response.getSessionMetadata());
@@ -111,8 +112,8 @@ public class RegistrationServiceClient implements Managed {
 
   @Deprecated
   public CompletableFuture<byte[]> createRegistrationSession(final Phonenumber.PhoneNumber phoneNumber,
-      final Duration timeout) {
-    return createRegistrationSessionSession(phoneNumber, timeout)
+      final boolean accountExistsWithPhoneNumber, final Duration timeout) {
+    return createRegistrationSessionSession(phoneNumber, accountExistsWithPhoneNumber, timeout)
         .thenApply(RegistrationServiceSession::id);
   }
 
diff --git a/service/src/main/proto/RegistrationService.proto b/service/src/main/proto/RegistrationService.proto
index 8f8c2ae7f..ea3f33ca2 100644
--- a/service/src/main/proto/RegistrationService.proto
+++ b/service/src/main/proto/RegistrationService.proto
@@ -35,6 +35,12 @@ message CreateRegistrationSessionRequest {
    * The phone number for which to create a new registration session.
    */
   uint64 e164 = 1;
+
+  /**
+   * Indicates whether an account already exists with the given e164 (i.e. this
+   * session represents a "re-registration" attempt).
+   */
+  bool account_exists_with_e164 = 2;
 }
 
 message CreateRegistrationSessionResponse {
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerTest.java
index 54c5520ab..e150c7ceb 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerTest.java
@@ -9,6 +9,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyList;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.argThat;
@@ -386,7 +387,7 @@ class AccountControllerTest {
 
   @Test
   void testGetFcmPreauth() throws NumberParseException {
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(new byte[16]));
 
     when(pendingAccountsManager.getCodeForNumber(SENDER)).thenReturn(Optional.empty());
@@ -401,7 +402,7 @@ class AccountControllerTest {
     final ArgumentCaptor<String> challengeTokenCaptor = ArgumentCaptor.forClass(String.class);
 
     verify(registrationServiceClient).createRegistrationSession(
-        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), any());
+        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), anyBoolean(), any());
 
     verify(pushNotificationManager).sendRegistrationChallengeNotification(
         eq("mytoken"), eq(PushNotification.TokenType.FCM), challengeTokenCaptor.capture());
@@ -411,7 +412,7 @@ class AccountControllerTest {
 
   @Test
   void testGetFcmPreauthIvoryCoast() throws NumberParseException {
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(new byte[16]));
 
     Response response = resources.getJerseyTest()
@@ -424,7 +425,7 @@ class AccountControllerTest {
     final ArgumentCaptor<String> challengeTokenCaptor = ArgumentCaptor.forClass(String.class);
 
     verify(registrationServiceClient).createRegistrationSession(
-        eq(PhoneNumberUtil.getInstance().parse("+2250707312345", null)), any());
+        eq(PhoneNumberUtil.getInstance().parse("+2250707312345", null)), anyBoolean(), any());
 
     verify(pushNotificationManager).sendRegistrationChallengeNotification(
         eq("mytoken"), eq(PushNotification.TokenType.FCM), challengeTokenCaptor.capture());
@@ -434,7 +435,7 @@ class AccountControllerTest {
 
   @Test
   void testGetApnPreauth() throws NumberParseException {
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(new byte[16]));
 
     when(pendingAccountsManager.getCodeForNumber(SENDER)).thenReturn(Optional.empty());
@@ -449,7 +450,7 @@ class AccountControllerTest {
     final ArgumentCaptor<String> challengeTokenCaptor = ArgumentCaptor.forClass(String.class);
 
     verify(registrationServiceClient).createRegistrationSession(
-        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), any());
+        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), anyBoolean(), any());
 
     verify(pushNotificationManager).sendRegistrationChallengeNotification(
         eq("mytoken"), eq(PushNotification.TokenType.APN_VOIP), challengeTokenCaptor.capture());
@@ -459,7 +460,7 @@ class AccountControllerTest {
 
   @Test
   void testGetApnPreauthExplicitVoip() throws NumberParseException {
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(new byte[16]));
 
     when(pendingAccountsManager.getCodeForNumber(SENDER)).thenReturn(Optional.empty());
@@ -475,7 +476,7 @@ class AccountControllerTest {
     final ArgumentCaptor<String> challengeTokenCaptor = ArgumentCaptor.forClass(String.class);
 
     verify(registrationServiceClient).createRegistrationSession(
-        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), any());
+        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), anyBoolean(), any());
 
     verify(pushNotificationManager).sendRegistrationChallengeNotification(
         eq("mytoken"), eq(PushNotification.TokenType.APN_VOIP), challengeTokenCaptor.capture());
@@ -485,7 +486,7 @@ class AccountControllerTest {
 
   @Test
   void testGetApnPreauthExplicitNoVoip() throws NumberParseException {
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(new byte[16]));
 
     when(pendingAccountsManager.getCodeForNumber(SENDER)).thenReturn(Optional.empty());
@@ -501,7 +502,7 @@ class AccountControllerTest {
     final ArgumentCaptor<String> challengeTokenCaptor = ArgumentCaptor.forClass(String.class);
 
     verify(registrationServiceClient).createRegistrationSession(
-        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), any());
+        eq(PhoneNumberUtil.getInstance().parse(SENDER, null)), anyBoolean(), any());
 
     verify(pushNotificationManager).sendRegistrationChallengeNotification(
         eq("mytoken"), eq(PushNotification.TokenType.APN), challengeTokenCaptor.capture());
@@ -546,7 +547,7 @@ class AccountControllerTest {
   void testGetPreauthExistingSession() throws NumberParseException {
     final String existingPushCode = "existing-push-code";
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(new byte[16]));
 
     when(pendingAccountsManager.getCodeForNumber(SENDER)).thenReturn(
@@ -561,7 +562,7 @@ class AccountControllerTest {
 
     final ArgumentCaptor<String> challengeTokenCaptor = ArgumentCaptor.forClass(String.class);
 
-    verify(registrationServiceClient, never()).createRegistrationSession(any(), any());
+    verify(registrationServiceClient, never()).createRegistrationSession(any(), anyBoolean(), any());
 
     verify(pushNotificationManager).sendRegistrationChallengeNotification(
         eq("mytoken"), eq(PushNotification.TokenType.APN_VOIP), challengeTokenCaptor.capture());
@@ -571,7 +572,7 @@ class AccountControllerTest {
 
   @Test
   void testGetPreauthExistingSessionWithoutPushCode() throws NumberParseException {
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(new byte[16]));
 
     when(pendingAccountsManager.getCodeForNumber(SENDER)).thenReturn(
@@ -586,7 +587,7 @@ class AccountControllerTest {
 
     final ArgumentCaptor<String> challengeTokenCaptor = ArgumentCaptor.forClass(String.class);
 
-    verify(registrationServiceClient, never()).createRegistrationSession(any(), any());
+    verify(registrationServiceClient, never()).createRegistrationSession(any(), anyBoolean(), any());
 
     verify(pushNotificationManager).sendRegistrationChallengeNotification(
         eq("mytoken"), eq(PushNotification.TokenType.APN_VOIP), challengeTokenCaptor.capture());
@@ -624,7 +625,7 @@ class AccountControllerTest {
   void testSendCode() {
     final byte[] sessionId = "session-id".getBytes(StandardCharsets.UTF_8);
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
@@ -648,7 +649,7 @@ class AccountControllerTest {
 
   @Test
   void testSendCodeRateLimited() {
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.failedFuture(new RateLimitExceededException(Duration.ofMinutes(10), true)));
 
     Response response =
@@ -709,7 +710,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -732,7 +733,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -785,7 +786,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -809,7 +810,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -834,7 +835,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -944,7 +945,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -975,7 +976,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -998,7 +999,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
@@ -2092,7 +2093,7 @@ class AccountControllerTest {
     when(registrationServiceClient.sendRegistrationCode(any(), any(), any(), any(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
-    when(registrationServiceClient.createRegistrationSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.completedFuture(sessionId));
 
     Response response =
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
index e9e3f994f..9b62bbb82 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
@@ -11,7 +11,9 @@ import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
@@ -19,6 +21,8 @@ import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.when;
 
 import com.google.common.net.HttpHeaders;
+import com.google.i18n.phonenumbers.NumberParseException;
+import com.google.i18n.phonenumbers.PhoneNumberUtil;
 import io.dropwizard.testing.junit5.DropwizardExtensionsSupport;
 import io.dropwizard.testing.junit5.ResourceExtension;
 import java.io.IOException;
@@ -46,6 +50,7 @@ import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.mockito.ArgumentCaptor;
 import org.whispersystems.textsecuregcm.captcha.AssessmentResult;
 import org.whispersystems.textsecuregcm.captcha.RegistrationCaptchaManager;
@@ -62,6 +67,8 @@ import org.whispersystems.textsecuregcm.registration.RegistrationServiceClient;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceException;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceSenderException;
 import org.whispersystems.textsecuregcm.registration.VerificationSession;
+import org.whispersystems.textsecuregcm.storage.Account;
+import org.whispersystems.textsecuregcm.storage.AccountsManager;
 import org.whispersystems.textsecuregcm.storage.RegistrationRecoveryPasswordsManager;
 import org.whispersystems.textsecuregcm.storage.VerificationSessionManager;
 import org.whispersystems.textsecuregcm.util.SystemMapper;
@@ -81,6 +88,7 @@ class VerificationControllerTest {
   private final RegistrationRecoveryPasswordsManager registrationRecoveryPasswordsManager = mock(
       RegistrationRecoveryPasswordsManager.class);
   private final RateLimiters rateLimiters = mock(RateLimiters.class);
+  private final AccountsManager accountsManager = mock(AccountsManager.class);
   private final Clock clock = Clock.systemUTC();
 
   private final RateLimiter captchaLimiter = mock(RateLimiter.class);
@@ -96,7 +104,7 @@ class VerificationControllerTest {
       .setTestContainerFactory(new GrizzlyWebTestContainerFactory())
       .addResource(
           new VerificationController(registrationServiceClient, verificationSessionManager, pushNotificationManager,
-              registrationCaptchaManager, registrationRecoveryPasswordsManager, rateLimiters, clock))
+              registrationCaptchaManager, registrationRecoveryPasswordsManager, rateLimiters, accountsManager, clock))
       .build();
 
   @BeforeEach
@@ -105,6 +113,8 @@ class VerificationControllerTest {
         .thenReturn(captchaLimiter);
     when(rateLimiters.getVerificationPushChallengeLimiter())
         .thenReturn(pushChallengeLimiter);
+
+    when(accountsManager.getByE164(any())).thenReturn(Optional.empty());
   }
 
   @ParameterizedTest
@@ -153,7 +163,7 @@ class VerificationControllerTest {
 
   @Test
   void createSessionRateLimited() {
-    when(registrationServiceClient.createRegistrationSessionSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSessionSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.failedFuture(new RateLimitExceededException(null, true)));
 
     final Invocation.Builder request = resources.getJerseyTest()
@@ -167,7 +177,7 @@ class VerificationControllerTest {
 
   @Test
   void createSessionRegistrationServiceError() {
-    when(registrationServiceClient.createRegistrationSessionSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSessionSession(any(), anyBoolean(), any()))
         .thenReturn(CompletableFuture.failedFuture(new RuntimeException("expected service error")));
 
     final Invocation.Builder request = resources.getJerseyTest()
@@ -183,7 +193,7 @@ class VerificationControllerTest {
   @MethodSource
   void createSessionSuccess(final String pushToken, final String pushTokenType,
       final List<VerificationSession.Information> expectedRequestedInformation) {
-    when(registrationServiceClient.createRegistrationSessionSession(any(), any()))
+    when(registrationServiceClient.createRegistrationSessionSession(any(), anyBoolean(), any()))
         .thenReturn(
             CompletableFuture.completedFuture(
                 new RegistrationServiceSession(SESSION_ID, NUMBER, false, null, null, null,
@@ -214,6 +224,37 @@ class VerificationControllerTest {
     );
   }
 
+  @ParameterizedTest
+  @ValueSource(booleans = {true, false})
+  void createSessionReregistration(final boolean isReregistration) throws NumberParseException {
+    when(registrationServiceClient.createRegistrationSessionSession(any(), anyBoolean(), any()))
+        .thenReturn(
+            CompletableFuture.completedFuture(
+                new RegistrationServiceSession(SESSION_ID, NUMBER, false, null, null, null,
+                    SESSION_EXPIRATION_SECONDS)));
+
+    when(verificationSessionManager.insert(any(), any()))
+        .thenReturn(CompletableFuture.completedFuture(null));
+
+    when(accountsManager.getByE164(NUMBER))
+        .thenReturn(isReregistration ? Optional.of(mock(Account.class)) : Optional.empty());
+
+    final Invocation.Builder request = resources.getJerseyTest()
+        .target("/v1/verification/session")
+        .request()
+        .header(HttpHeaders.X_FORWARDED_FOR, "127.0.0.1");
+
+    try (final Response response = request.post(Entity.json(createSessionJson(NUMBER, null, null)))) {
+      assertEquals(HttpStatus.SC_OK, response.getStatus());
+
+      verify(registrationServiceClient).createRegistrationSessionSession(
+          eq(PhoneNumberUtil.getInstance().parse(NUMBER, null)),
+          eq(isReregistration),
+          any()
+      );
+    }
+  }
+
   @Test
   void patchSessionMalformedId() {
     final String invalidSessionId = "()()()";