Enable runtime metrics by default

tracer/src/Datadog.Trace/Configuration/TracerSettings.cs

@@ -420,10 +420,11 @@ _ when x.ToBoolean() is { } boolean => boolean,
                                                value => string.Equals(value, "none", StringComparison.OrdinalIgnoreCase)
                                                             ? ParsingResult<bool>.Success(result: false)
                                                             : ParsingResult<bool>.Failure());
+
             _runtimeMetricsEnabled = config
                                    .WithKeys(ConfigurationKeys.RuntimeMetricsEnabled)
                                    .AsBoolResult()
-                                   .OverrideWith(in otelRuntimeMetricsEnabled, ErrorLog, defaultValue: false);
+                                   .OverrideWith(in otelRuntimeMetricsEnabled, ErrorLog, defaultValue: EnvironmentHelpers.ShouldActivateRuntimeMetrics(isRunningInCiVisibility));
 
             DataPipelineEnabled = config
                                   .WithKeys(ConfigurationKeys.TraceDataPipelineEnabled)

tracer/src/Datadog.Trace/FrameworkDescription.cs

@@ -68,6 +68,11 @@ public static bool IsNet5()
             return Environment.Version.Major >= 5;
         }
 
+        public static bool IsLowerThanNet9()
+        {
+            return Environment.Version.Major < 9;
+        }
+
         public bool IsWindows()
         {
             return string.Equals(OSPlatform, OSPlatformName.Windows, StringComparison.OrdinalIgnoreCase);

tracer/src/Datadog.Trace/Util/EnvironmentHelpers.cs

@@ -154,6 +154,24 @@ public static bool IsGoogleCloudFunctions()
                     EnvironmentVariableExists(ConfigurationKeys.GCPFunction.DeprecatedProjectKey));
         }
 
+        /// <summary>
+        /// Activate runtime metrics only on >= net9 or NetFx
+        /// </summary>
+        /// <param name="isRunningInCiVisibility">isRunningInCiVisibility</param>
+        /// <returns>whether to activate it or not</returns>
+        public static bool ShouldActivateRuntimeMetrics(bool isRunningInCiVisibility)
+        {
+            // only activate runtime metrics by default from net9 or netframework
+            var shouldActivateRuntimeMetrics = !isRunningInCiVisibility;
+#if !NETFRAMEWORK
+            if (shouldActivateRuntimeMetrics && FrameworkDescription.IsLowerThanNet9())
+            {
+                shouldActivateRuntimeMetrics = false;
+            }
+#endif
+            return shouldActivateRuntimeMetrics;
+        }
+
         /// <summary>
         /// Checks if the specified environment variable exists in the current environment.
         /// </summary>