diff --git a/src/Runner.Worker/ExecutionContext.cs b/src/Runner.Worker/ExecutionContext.cs
index 545340d36..b70968193 100644
--- a/src/Runner.Worker/ExecutionContext.cs
+++ b/src/Runner.Worker/ExecutionContext.cs
@@ -858,6 +858,10 @@ namespace GitHub.Runner.Worker
             {
                 _record.ParentId = parentTimelineRecordId;
             }
+            else if (parentTimelineRecordId == null)
+            {
+                _record.AgentPlatform = VarUtil.OS;
+            }
 
             var configuration = HostContext.GetService<IConfigurationStore>();
             _record.WorkerName = configuration.GetSettings().AgentName;
diff --git a/src/Sdk/DTWebApi/WebApi/TimelineRecord.cs b/src/Sdk/DTWebApi/WebApi/TimelineRecord.cs
index 8403c3ac2..a14bded63 100644
--- a/src/Sdk/DTWebApi/WebApi/TimelineRecord.cs
+++ b/src/Sdk/DTWebApi/WebApi/TimelineRecord.cs
@@ -38,6 +38,7 @@ namespace GitHub.DistributedTask.WebApi
             this.RefName = recordToBeCloned.RefName;
             this.ErrorCount = recordToBeCloned.ErrorCount;
             this.WarningCount = recordToBeCloned.WarningCount;
+            this.AgentPlatform = recordToBeCloned.AgentPlatform;
 
             if (recordToBeCloned.Log != null)
             {
@@ -254,6 +255,13 @@ namespace GitHub.DistributedTask.WebApi
             set;
         }
 
+        [DataMember(Order = 132, EmitDefaultValue = false)]
+        public string AgentPlatform
+        {
+            get;
+            set;
+        }
+
         public IList<TimelineAttempt> PreviousAttempts
         {
             get