diff --git a/libraries/src/AWS.Lambda.Powertools.Metrics/Model/MetricDirective.cs b/libraries/src/AWS.Lambda.Powertools.Metrics/Model/MetricDirective.cs
index 7615ba65..f8ccad76 100644
--- a/libraries/src/AWS.Lambda.Powertools.Metrics/Model/MetricDirective.cs
+++ b/libraries/src/AWS.Lambda.Powertools.Metrics/Model/MetricDirective.cs
@@ -105,23 +105,23 @@ private MetricDirective(string nameSpace, List<MetricDefinition> metrics, List<D
     /// </summary>
     /// <value>All dimension keys.</value>
     [JsonPropertyName("Dimensions")]
-    public List<List<string>> AllDimensionKeys
+    public List<string> AllDimensionKeys
     {
         get
         {
             var defaultKeys = DefaultDimensions
                 .Where(d => d.DimensionKeys.Any())
-                .Select(s => s.DimensionKeys)
+                .SelectMany(s => s.DimensionKeys)
                 .ToList();
 
             var keys = Dimensions
                 .Where(d => d.DimensionKeys.Any())
-                .Select(s => s.DimensionKeys)
+                .SelectMany(s => s.DimensionKeys)
                 .ToList();
 
             defaultKeys.AddRange(keys);
 
-            if (defaultKeys.Count == 0) defaultKeys.Add(new List<string>());
+            if (defaultKeys.Count == 0) defaultKeys = new List<string>();
 
             return defaultKeys;
         }
diff --git a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/ClearDimensionsTests.cs b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/ClearDimensionsTests.cs
index 0a46d6fd..1ac09fbe 100644
--- a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/ClearDimensionsTests.cs
+++ b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/ClearDimensionsTests.cs
@@ -22,7 +22,7 @@ public void WhenClearAllDimensions_NoDimensionsInOutput()
         var metricsOutput = consoleOut.ToString();
 
         // Assert
-        Assert.Contains("{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name\",\"Unit\":\"Count\"}],\"Dimensions\":[[]]", metricsOutput);
+        Assert.Contains("{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name\",\"Unit\":\"Count\"}],\"Dimensions\":[]", metricsOutput);
         
         // Reset
         MetricsAspect.ResetForTest();
diff --git a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/EMFValidationTests.cs b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/EMFValidationTests.cs
index cd89ced5..79c275ae 100644
--- a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/EMFValidationTests.cs
+++ b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/EMFValidationTests.cs
@@ -79,12 +79,12 @@ public void WhenMaxMetricsAreAdded_FlushAutomatically()
 
             // flush when it reaches MaxMetrics
             Assert.Contains(
-                "{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name 1\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 2\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 3\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 4\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 5\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 6\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 7\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 8\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 9\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 10\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 11\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 12\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 13\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 14\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 15\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 16\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 17\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 18\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 19\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 20\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 21\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 22\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 23\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 24\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 25\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 26\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 27\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 28\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 29\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 30\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 31\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 32\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 33\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 34\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 35\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 36\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 37\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 38\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 39\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 40\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 41\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 42\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 43\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 44\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 45\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 46\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 47\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 48\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 49\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 50\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 51\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 52\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 53\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 54\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 55\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 56\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 57\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 58\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 59\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 60\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 61\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 62\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 63\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 64\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 65\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 66\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 67\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 68\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 69\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 70\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 71\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 72\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 73\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 74\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 75\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 76\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 77\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 78\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 79\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 80\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 81\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 82\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 83\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 84\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 85\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 86\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 87\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 88\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 89\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 90\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 91\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 92\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 93\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 94\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 95\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 96\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 97\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 98\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 99\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 100\",\"Unit\":\"Count\"}],\"Dimensions\":[[\"Service\"]]",
+                "{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name 1\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 2\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 3\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 4\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 5\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 6\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 7\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 8\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 9\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 10\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 11\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 12\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 13\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 14\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 15\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 16\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 17\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 18\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 19\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 20\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 21\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 22\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 23\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 24\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 25\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 26\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 27\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 28\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 29\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 30\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 31\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 32\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 33\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 34\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 35\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 36\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 37\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 38\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 39\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 40\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 41\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 42\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 43\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 44\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 45\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 46\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 47\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 48\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 49\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 50\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 51\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 52\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 53\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 54\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 55\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 56\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 57\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 58\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 59\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 60\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 61\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 62\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 63\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 64\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 65\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 66\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 67\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 68\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 69\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 70\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 71\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 72\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 73\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 74\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 75\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 76\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 77\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 78\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 79\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 80\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 81\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 82\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 83\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 84\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 85\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 86\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 87\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 88\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 89\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 90\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 91\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 92\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 93\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 94\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 95\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 96\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 97\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 98\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 99\",\"Unit\":\"Count\"},{\"Name\":\"Metric Name 100\",\"Unit\":\"Count\"}],\"Dimensions\":[\"Service\"]",
                 metricsOutput[0]);
 
             // flush the (MaxMetrics + 1) item only
             Assert.Contains(
-                "{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name 101\",\"Unit\":\"Count\"}],\"Dimensions\":[[\"Service\"]",
+                "{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name 101\",\"Unit\":\"Count\"}],\"Dimensions\":[\"Service\"]",
                 metricsOutput[1]);
         }
 
@@ -105,7 +105,7 @@ public void WhenMaxDataPointsAreAddedToTheSameMetric_FlushAutomatically()
                 metricsOutput[0]);
 
             // flush the (MaxMetrics + 1) item only
-            Assert.Contains("[[\"Service\"]]}]},\"Service\":\"testService\",\"Metric Name\":100}", metricsOutput[1]);
+            Assert.Contains("[\"Service\"]}]},\"Service\":\"testService\",\"Metric Name\":100}", metricsOutput[1]);
         }
 
         [Trait("Category", "EMFLimits")]
@@ -141,11 +141,28 @@ public void WhenDimensionsAreAdded_MustExistAsMembers()
             var metricsOutput = _consoleOut.ToString();
 
             // Assert
-            Assert.Contains("\"Dimensions\":[[\"Service\"],[\"functionVersion\"]]"
+            Assert.Contains("\"Dimensions\":[\"Service\",\"functionVersion\"]"
                 , metricsOutput);
             Assert.Contains("\"Service\":\"testService\",\"functionVersion\":\"$LATEST\""
                 , metricsOutput);
         }
+        
+        [Trait("Category", "SchemaValidation")]
+        [Fact]
+        public void When_Multiple_DimensionsAreAdded_MustExistAsMembers()
+        {
+            // Act
+            _handler.AddMultipleDimensions();
+
+            var metricsOutput = _consoleOut.ToString();
+
+            // Assert
+            Assert.Contains("\"CloudWatchMetrics\":[{\"Namespace\":\"ns1\",\"Metrics\":[{\"Name\":\"Lambda Execute\",\"Unit\":\"Count\",\"StorageResolution\":1}],\"Dimensions\":[\"Type\",\"Service\"]}]},\"Type\":\"Start\",\"Service\":\"service_undefined\",\"Lambda Execute\":1}", metricsOutput);
+            
+            Assert.Contains("\"CloudWatchMetrics\":[{\"Namespace\":\"ns2\",\"Metrics\":[{\"Name\":\"Lambda Execute\",\"Unit\":\"Count\",\"StorageResolution\":1}],\"Dimensions\":[\"Type\",\"SessionId\",\"Service\"]}]},\"Type\":\"Start\",\"SessionId\":\"Unset\",\"Service\":\"service_undefined\",\"Lambda Execute\":1}", metricsOutput);
+            
+            Assert.Contains("\"CloudWatchMetrics\":[{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Lambda Execute\",\"Unit\":\"Count\",\"StorageResolution\":1}],\"Dimensions\":[\"Service\",\"Default\",\"SessionId\",\"Type\"]}]},\"Service\":\"testService\",\"Default\":\"Initial\",\"SessionId\":\"MySessionId\",\"Type\":\"Start\",\"Lambda Execute\":1}", metricsOutput);
+        }
 
         [Trait("Category", "MetricsImplementation")]
         [Fact]
@@ -192,7 +209,7 @@ public void WhenDefaultDimensionsSet_ValidInitialization()
             var result = _consoleOut.ToString();
 
             // Assert
-            Assert.Contains($"\"Dimensions\":[[\"Service\"],[\"{key}\"]", result);
+            Assert.Contains($"\"Dimensions\":[\"Service\",\"{key}\"]", result);
             Assert.Contains($"\"CustomDefaultDimension\":\"{value}\"", result);
         }
 
@@ -229,7 +246,7 @@ public void WhenDefaultDimensionSet_IgnoreDuplicates()
             var result = _consoleOut.ToString();
 
             // Assert
-            Assert.Contains("\"Dimensions\":[[\"Service\"],[\"CustomDefaultDimension\"]", result);
+            Assert.Contains("\"Dimensions\":[\"Service\",\"CustomDefaultDimension\"]", result);
             Assert.Contains("\"CustomDefaultDimension\":\"CustomDefaultDimensionValue\"", result);
         }
 
@@ -243,7 +260,7 @@ public void WhenMetricsAndMetadataAdded_ValidateOutput()
 
             // Assert
             Assert.Contains(
-                "CloudWatchMetrics\":[{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Time\",\"Unit\":\"Milliseconds\"}],\"Dimensions\":[[\"Service\"],[\"functionVersion\"]]}]},\"Service\":\"testService\",\"functionVersion\":\"$LATEST\",\"Time\":100.7,\"env\":\"dev\"}"
+                "CloudWatchMetrics\":[{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Time\",\"Unit\":\"Milliseconds\"}],\"Dimensions\":[\"Service\",\"functionVersion\"]}]},\"Service\":\"testService\",\"functionVersion\":\"$LATEST\",\"Time\":100.7,\"env\":\"dev\"}"
                 , result);
         }
 
@@ -258,7 +275,7 @@ public void When_Metrics_And_Metadata_Added_With_Same_Key_Should_Only_Write_Metr
             // Assert
             // No Metadata key was added
             Assert.Contains(
-                "CloudWatchMetrics\":[{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Time\",\"Unit\":\"Milliseconds\"}],\"Dimensions\":[[\"Service\"],[\"functionVersion\"]]}]},\"Service\":\"testService\",\"functionVersion\":\"$LATEST\",\"Time\":100.7}"
+                "CloudWatchMetrics\":[{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Time\",\"Unit\":\"Milliseconds\"}],\"Dimensions\":[\"Service\",\"functionVersion\"]}]},\"Service\":\"testService\",\"functionVersion\":\"$LATEST\",\"Time\":100.7}"
                 , result);
         }
 
@@ -320,7 +337,7 @@ public async Task WhenMetricsAsyncRaceConditionItemSameKeyExists_ValidateLock()
 
             // Assert
             Assert.Contains(
-                "{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name\",\"Unit\":\"Count\"}],\"Dimensions\":[[\"Service\"]]",
+                "{\"Namespace\":\"dotnet-powertools-test\",\"Metrics\":[{\"Name\":\"Metric Name\",\"Unit\":\"Count\"}],\"Dimensions\":[\"Service\"]",
                 metricsOutput);
         }
 
diff --git a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandler.cs b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandler.cs
index 8447575d..e29e99a9 100644
--- a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandler.cs
+++ b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandler.cs
@@ -38,6 +38,27 @@ public void AddDimensions()
         Metrics.AddDimension("functionVersion", "$LATEST");
         Metrics.AddMetric("TestMetric", 1, MetricUnit.Count);
     }
+    
+    [Metrics(Namespace = "dotnet-powertools-test", Service = "testService")]
+    public void AddMultipleDimensions()
+    {
+        Metrics.SetDefaultDimensions(new Dictionary<string, string> {
+            { "Default", "Initial" }
+        });
+        Metrics.PushSingleMetric("Lambda Execute", 1, MetricUnit.Count, metricResolution: MetricResolution.High, nameSpace: "ns1",
+            defaultDimensions: new Dictionary<string, string> {
+                { "Type", "Start" }
+            });
+        
+        Metrics.PushSingleMetric("Lambda Execute", 1, MetricUnit.Count, metricResolution: MetricResolution.High,  nameSpace: "ns2",
+            defaultDimensions: new Dictionary<string, string> {
+                { "Type", "Start" },
+                { "SessionId", "Unset" }
+            });
+        Metrics.AddMetric("Lambda Execute", 1, MetricUnit.Count, MetricResolution.High);
+        Metrics.AddDimension("SessionId", "MySessionId");
+        Metrics.AddDimension("Type", "Start");
+    }
 
     [Metrics(Namespace = "dotnet-powertools-test", Service = "testService")]
     public void ClearDimensions()
diff --git a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandlerTests.cs b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandlerTests.cs
index 075da0a0..dd140b40 100644
--- a/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandlerTests.cs
+++ b/libraries/tests/AWS.Lambda.Powertools.Metrics.Tests/Handlers/FunctionHandlerTests.cs
@@ -85,7 +85,7 @@ public void When_LambdaContext_Should_Add_FunctioName_Dimension_CaptureColdStart
             metricsOutput);
         
         Assert.Contains(
-            "\"Metrics\":[{\"Name\":\"ColdStart\",\"Unit\":\"Count\"}],\"Dimensions\":[[\"FunctionName\"],[\"Service\"]]}]}",
+            "\"Metrics\":[{\"Name\":\"ColdStart\",\"Unit\":\"Count\"}],\"Dimensions\":[\"FunctionName\",\"Service\"]}]}",
             metricsOutput);
     }
     
@@ -108,7 +108,7 @@ public void When_LambdaContext_And_Parameter_Should_Add_FunctioName_Dimension_Ca
             metricsOutput);
         
         Assert.Contains(
-            "\"Metrics\":[{\"Name\":\"ColdStart\",\"Unit\":\"Count\"}],\"Dimensions\":[[\"FunctionName\"],[\"Service\"]]}]}",
+            "\"Metrics\":[{\"Name\":\"ColdStart\",\"Unit\":\"Count\"}],\"Dimensions\":[\"FunctionName\",\"Service\"]}]}",
             metricsOutput);
     }
     
@@ -125,7 +125,7 @@ public void When_No_LambdaContext_Should_Not_Add_FunctioName_Dimension_CaptureCo
             metricsOutput);
         
         Assert.Contains(
-            "\"Metrics\":[{\"Name\":\"MyMetric\",\"Unit\":\"None\"}],\"Dimensions\":[[\"Service\"]]}]},\"Service\":\"svc\",\"MyMetric\":1}",
+            "\"Metrics\":[{\"Name\":\"MyMetric\",\"Unit\":\"None\"}],\"Dimensions\":[\"Service\"]}]},\"Service\":\"svc\",\"MyMetric\":1}",
             metricsOutput);
     }
 
diff --git a/version.json b/version.json
index ffcfa3f8..ded38529 100644
--- a/version.json
+++ b/version.json
@@ -1,7 +1,7 @@
 {
 	"Core": {
 		"Logging": "1.6.1",
-		"Metrics": "1.7.1",
+		"Metrics": "1.8.0",
 		"Tracing": "1.5.2"
 	},
 	"Utilities": {