diff --git a/src/Cli/dotnet/Program.cs b/src/Cli/dotnet/Program.cs
index de1ebb9e6..6bbf479de 100644
--- a/src/Cli/dotnet/Program.cs
+++ b/src/Cli/dotnet/Program.cs
@@ -28,6 +28,13 @@ public class Program
 
         public static int Main(string[] args)
         {
+            // opt out of telemetry by default if the env var is unset
+            string telemetryValue = Environment.GetEnvironmentVariable("DOTNET_CLI_TELEMETRY_OPTOUT");
+            if (String.IsNullOrEmpty(telemetryValue))
+            {
+                Environment.SetEnvironmentVariable("DOTNET_CLI_TELEMETRY_OPTOUT", "1");
+            }
+
             DebugHelper.HandleDebugSwitch(ref args);
 
             // Capture the current timestamp to calculate the host overhead.