diff --git a/src/channels/adapter.ts b/src/channels/adapter.ts
index d8d8f9d..82247a1 100644
--- a/src/channels/adapter.ts
+++ b/src/channels/adapter.ts
@@ -56,6 +56,8 @@ export interface InboundEvent {
      * See InboundMessage.isMention for the full explanation.
      */
     isMention?: boolean;
+    /** True when the source is a group/channel thread, false for DMs. */
+    isGroup?: boolean;
   };
   replyTo?: DeliveryAddress;
 }
@@ -81,6 +83,8 @@ export interface InboundMessage {
    * router falls back to text-match against agent_group_name.
    */
   isMention?: boolean;
+  /** True when the source is a group/channel thread, false for DMs. */
+  isGroup?: boolean;
 }
 
 /** A file attachment to deliver alongside a message. */
diff --git a/src/index.ts b/src/index.ts
index d3de4d9..ea9fba6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -85,6 +85,7 @@ async function main(): Promise<void> {
             content: JSON.stringify(message.content),
             timestamp: message.timestamp,
             isMention: message.isMention,
+            isGroup: message.isGroup,
           },
         }).catch((err) => {
           log.error('Failed to route inbound message', { channelType: adapter.channelType, err });
diff --git a/src/router.ts b/src/router.ts
index 538c270..3cf0192 100644
--- a/src/router.ts
+++ b/src/router.ts
@@ -170,7 +170,7 @@ export async function routeInbound(event: InboundEvent): Promise<void> {
       channel_type: event.channelType,
       platform_id: event.platformId,
       name: null,
-      is_group: 0,
+      is_group: event.message.isGroup ? 1 : 0,
       unknown_sender_policy: 'request_approval',
       denied_at: null,
       created_at: new Date().toISOString(),