diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
index 54fa87548..626aa1702 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
@@ -79,6 +79,7 @@ import org.whispersystems.textsecuregcm.badges.ConfiguredProfileBadgeConverter;
 import org.whispersystems.textsecuregcm.badges.ResourceBundleLevelTranslator;
 import org.whispersystems.textsecuregcm.configuration.DirectoryServerConfiguration;
 import org.whispersystems.textsecuregcm.configuration.dynamic.DynamicConfiguration;
+import org.whispersystems.textsecuregcm.controllers.AcceptNumericOnlineFlagRequestFilter;
 import org.whispersystems.textsecuregcm.controllers.AccountController;
 import org.whispersystems.textsecuregcm.controllers.AttachmentControllerV1;
 import org.whispersystems.textsecuregcm.controllers.AttachmentControllerV2;
@@ -610,7 +611,12 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
         .addFilter("RemoteDeprecationFilter", new RemoteDeprecationFilter(dynamicConfigurationManager))
         .addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), false, "/*");
 
+    // TODO Remove on or after 2022-03-01
+    final AcceptNumericOnlineFlagRequestFilter acceptNumericOnlineFlagRequestFilter =
+        new AcceptNumericOnlineFlagRequestFilter("v1/messages/multi_recipient");
+
     environment.jersey().register(new ContentLengthFilter(TrafficSource.HTTP));
+    environment.jersey().register(acceptNumericOnlineFlagRequestFilter);
     environment.jersey().register(MultiRecipientMessageProvider.class);
     environment.jersey().register(new MetricsApplicationEventListener(TrafficSource.HTTP));
     environment.jersey()
@@ -632,6 +638,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
             clientPresenceManager, retrySchedulingExecutor));
     webSocketEnvironment.jersey().register(new WebsocketRefreshApplicationEventListener(accountsManager, clientPresenceManager));
     webSocketEnvironment.jersey().register(new ContentLengthFilter(TrafficSource.WEBSOCKET));
+    webSocketEnvironment.jersey().register(acceptNumericOnlineFlagRequestFilter);
     webSocketEnvironment.jersey().register(MultiRecipientMessageProvider.class);
     webSocketEnvironment.jersey().register(new MetricsApplicationEventListener(TrafficSource.WEBSOCKET));
     webSocketEnvironment.jersey().register(new KeepAliveController(clientPresenceManager));
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AcceptNumericOnlineFlagRequestFilter.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AcceptNumericOnlineFlagRequestFilter.java
new file mode 100644
index 000000000..12ec73ff8
--- /dev/null
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AcceptNumericOnlineFlagRequestFilter.java
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2013-2021 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.controllers;
+
+import java.io.IOException;
+import javax.ws.rs.container.ContainerRequestContext;
+import javax.ws.rs.container.ContainerRequestFilter;
+import javax.ws.rs.container.PreMatching;
+
+@PreMatching
+public class AcceptNumericOnlineFlagRequestFilter implements ContainerRequestFilter {
+
+  private final String pathPrefix;
+
+  public AcceptNumericOnlineFlagRequestFilter(final String pathPrefix) {
+    this.pathPrefix = pathPrefix;
+  }
+
+  @Override
+  public void filter(final ContainerRequestContext requestContext) throws IOException {
+    if (requestContext.getUriInfo().getPath().startsWith(pathPrefix)) {
+      if ("1".equals(requestContext.getUriInfo().getQueryParameters().getFirst("online"))) {
+        requestContext.setRequestUri(requestContext.getUriInfo().getRequestUriBuilder()
+            .replaceQueryParam("online", "true")
+            .build());
+      }
+    }
+  }
+}
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AcceptNumericOnlineFlagRequestFilterTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AcceptNumericOnlineFlagRequestFilterTest.java
new file mode 100644
index 000000000..6e89a2780
--- /dev/null
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AcceptNumericOnlineFlagRequestFilterTest.java
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2013-2021 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.controllers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.dropwizard.testing.junit5.DropwizardExtensionsSupport;
+import io.dropwizard.testing.junit5.ResourceExtension;
+import javax.ws.rs.GET;
+import javax.ws.rs.Path;
+import javax.ws.rs.QueryParam;
+import org.glassfish.jersey.test.grizzly.GrizzlyWebTestContainerFactory;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+@ExtendWith(DropwizardExtensionsSupport.class)
+class AcceptNumericOnlineFlagRequestFilterTest {
+
+  @Path("/test")
+  public static class TestResource {
+
+    @Path("/convert-boolean")
+    @GET
+    public boolean convertBoolean(@QueryParam("online") final boolean online) {
+      return online;
+    }
+
+    @Path("/no-conversion")
+    @GET
+    public boolean noConversion(@QueryParam("online") final boolean online) {
+      return online;
+    }
+  }
+
+  private static final ResourceExtension RESOURCE_EXTENSION = ResourceExtension.builder()
+      .addProvider(new AcceptNumericOnlineFlagRequestFilter("test/convert-boolean"))
+      .setTestContainerFactory(new GrizzlyWebTestContainerFactory())
+      .addResource(new TestResource())
+      .build();
+
+  @ParameterizedTest
+  @CsvSource({
+      "/test/convert-boolean, true,  true",
+      "/test/convert-boolean, false, false",
+      "/test/convert-boolean, 1,     true",
+      "/test/convert-boolean, 0,     false",
+      "/test/no-conversion,   true,  true",
+      "/test/no-conversion,   false, false",
+      "/test/no-conversion,   1,     false",
+      "/test/no-conversion,   0,     false"
+  })
+  void filter(final String path, final String value, final boolean expected) {
+    final boolean response =
+        RESOURCE_EXTENSION.getJerseyTest()
+            .target(path)
+            .queryParam("online", value)
+            .request()
+            .get(boolean.class);
+
+    assertEquals(expected, response);
+  }
+}