diff --git a/library/kernel_api/protocols/relay_api.nim b/library/kernel_api/protocols/relay_api.nim
index b184d6011..7a80e1318 100644
--- a/library/kernel_api/protocols/relay_api.nim
+++ b/library/kernel_api/protocols/relay_api.nim
@@ -85,8 +85,8 @@ proc waku_relay_subscribe(
     callback: FFICallBack,
     userData: pointer,
     pubSubTopic: cstring,
+    contentTopic: cstring,
 ) {.ffi.} =
-  echo "Subscribing to topic: " & $pubSubTopic & " ..."
   proc onReceivedMessage(ctx: ptr FFIContext[Waku]): WakuRelayHandler =
     return proc(pubsubTopic: PubsubTopic, msg: WakuMessage) {.async.} =
       callEventCallback(ctx, "onReceivedMessage"):
@@ -94,21 +94,38 @@ proc waku_relay_subscribe(
 
   var cb = onReceivedMessage(ctx)
 
-  ctx.myLib[].node.subscribe(
-    (kind: SubscriptionKind.PubsubSub, topic: $pubsubTopic),
-    handler = WakuRelayHandler(cb),
-  ).isOkOr:
+  # If contentTopic is provided and non-empty, use ContentSub, otherwise use PubsubSub
+  let subscription =
+    if contentTopic != nil and len($contentTopic) > 0:
+      echo "Subscribing to content topic: " & $contentTopic & " ..."
+      (kind: SubscriptionKind.ContentSub, topic: $contentTopic)
+    else:
+      echo "Subscribing to pubsub topic: " & $pubSubTopic & " ..."
+      (kind: SubscriptionKind.PubsubSub, topic: $pubsubTopic)
+
+  ctx.myLib[].node.subscribe(subscription, handler = WakuRelayHandler(cb)).isOkOr:
     error "SUBSCRIBE failed", error = error
     return err($error)
   return ok("")
 
+# NOTE: When unsubscribing via contentTopic, this will unsubscribe from the entire
+# underlying pubsub topic/shard that the content topic maps to. This affects ALL
+# content topics on the same shard, not just the specified content topic.
 proc waku_relay_unsubscribe(
     ctx: ptr FFIContext[Waku],
     callback: FFICallBack,
     userData: pointer,
     pubSubTopic: cstring,
+    contentTopic: cstring,
 ) {.ffi.} =
-  ctx.myLib[].node.unsubscribe((kind: SubscriptionKind.PubsubSub, topic: $pubsubTopic)).isOkOr:
+  # If contentTopic is provided and non-empty, use ContentUnsub, otherwise use PubsubUnsub
+  let subscription =
+    if contentTopic != nil and len($contentTopic) > 0:
+      (kind: SubscriptionKind.ContentUnsub, topic: $contentTopic)
+    else:
+      (kind: SubscriptionKind.PubsubUnsub, topic: $pubsubTopic)
+
+  ctx.myLib[].node.unsubscribe(subscription).isOkOr:
     error "UNSUBSCRIBE failed", error = error
     return err($error)
 
diff --git a/library/libwaku.h b/library/libwaku.h
index 67c89c7c2..011912853 100644
--- a/library/libwaku.h
+++ b/library/libwaku.h
@@ -85,7 +85,8 @@ extern "C"
   int waku_relay_subscribe(void *ctx,
                            FFICallBack callback,
                            void *userData,
-                           const char *pubSubTopic);
+                           const char *pubSubTopic,
+                           const char *contentTopic);
 
   int waku_relay_add_protected_shard(void *ctx,
                                      FFICallBack callback,
@@ -97,7 +98,8 @@ extern "C"
   int waku_relay_unsubscribe(void *ctx,
                              FFICallBack callback,
                              void *userData,
-                             const char *pubSubTopic);
+                             const char *pubSubTopic,
+                             const char *contentTopic);
 
   int waku_filter_subscribe(void *ctx,
                             FFICallBack callback,