diff --git a/opencda/core/common/communication/messages/ack.proto b/opencda/core/common/communication/messages/ack.proto
deleted file mode 100644
index 9a454497..00000000
--- a/opencda/core/common/communication/messages/ack.proto
+++ /dev/null
@@ -1,6 +0,0 @@
-syntax = "proto3";
-
-package capi;
-
-message AckMessage {
-}
diff --git a/opencda/core/common/communication/messages/capi.proto b/opencda/core/common/communication/messages/capi.proto
index 10b4051e..9e4a475c 100644
--- a/opencda/core/common/communication/messages/capi.proto
+++ b/opencda/core/common/communication/messages/capi.proto
@@ -2,15 +2,13 @@ syntax = "proto3";
 
 package capi;
 
-import "ack.proto";
 import "artery.proto";
 import "opencda.proto";
 
 message Message {
     int64 order = 1;
     oneof message {
-        AckMessage ack = 2;
-        OpenCDAMessage opencda = 3;
-        ArteryMessage artery = 4;
+        OpenCDAMessage opencda = 2;
+        ArteryMessage artery = 3;
     }
 }
diff --git a/opencda/scenario_testing/scenario.py b/opencda/scenario_testing/scenario.py
index ee5aba0f..19211c6a 100644
--- a/opencda/scenario_testing/scenario.py
+++ b/opencda/scenario_testing/scenario.py
@@ -93,7 +93,7 @@ def __init__(self, opt: argparse.Namespace, scenario_params: omegaconf.OmegaConf
         if opt.with_capi:
             from opencda.core.common.communication import toolchain
 
-            toolchain.CommunicationToolchain.handle_messages(["entity", "opencda", "artery", "capi", "ack"])
+            toolchain.CommunicationToolchain.handle_messages(["entity", "opencda", "artery", "capi"])
             from opencda.core.common.communication.communication_manager import CommunicationManager
             from opencda.core.common.communication.payload_handler import PayloadHandler