public class CIMLabelClass : CIMObject, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

public async Task CreatingAnAnnotationFeature(Geodatabase geodatabase)
{
  await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
  {
    using (AnnotationFeatureClass annotationFeatureClass = geodatabase.OpenDataset<AnnotationFeatureClass>("Annotation // feature // class // name"))
    using (AnnotationFeatureClassDefinition annotationFeatureClassDefinition = annotationFeatureClass.GetDefinition())
    using (RowBuffer rowBuffer = annotationFeatureClass.CreateRowBuffer())
    using (AnnotationFeature annotationFeature = annotationFeatureClass.CreateRow(rowBuffer))
    {
      annotationFeature.SetAnnotationClassID(0);
      annotationFeature.SetStatus(AnnotationStatus.Placed);

      // Get the annotation labels from the label collection
      IReadOnlyList<CIMLabelClass> labelClasses = 
        annotationFeatureClassDefinition.GetLabelClassCollection();

      // Setup the symbol reference with the symbol id and the text symbol
      CIMSymbolReference cimSymbolReference = new CIMSymbolReference();
      cimSymbolReference.Symbol = labelClasses[0].TextSymbol.Symbol;
      cimSymbolReference.SymbolName = labelClasses[0].TextSymbol.SymbolName;

      // Setup the text graphic
      CIMTextGraphic cimTextGraphic = new CIMTextGraphic();
      cimTextGraphic.Text = "Charlotte, North Carolina";
      cimTextGraphic.Shape = new MapPointBuilderEx(new Coordinate2D(-80.843, 35.234), SpatialReferences.WGS84).ToGeometry();
      cimTextGraphic.Symbol = cimSymbolReference;

      // Set the symbol reference on the graphic and store
      annotationFeature.SetGraphic(cimTextGraphic);
      annotationFeature.Store();
    }
  });
}

// Creating a Cities annotation feature class
// with following user defined fields
// Name 
// GlobalID

// Annotation feature class name
string annotationFeatureClassName = "CitiesAnnotation";

// Create user defined attribute fields for annotation feature class 
FieldDescription globalIDFieldDescription = FieldDescription.CreateGlobalIDField();
FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 255);

// Create a list of all field descriptions
List<FieldDescription> fieldDescriptions = new List<FieldDescription> { globalIDFieldDescription, nameFieldDescription };

// Create a ShapeDescription object
ShapeDescription shapeDescription = new ShapeDescription(GeometryType.Polygon, spatialReference);

// Create general placement properties for Maplex engine 
CIMMaplexGeneralPlacementProperties generalPlacementProperties =
  new CIMMaplexGeneralPlacementProperties
  {
    AllowBorderOverlap = true,
    PlacementQuality = MaplexQualityType.High,
    DrawUnplacedLabels = true,
    InvertedLabelTolerance = 1.0,
    RotateLabelWithDisplay = true,
    UnplacedLabelColor = new CIMRGBColor
    {
      R = 0,
      G = 255,
      B = 0,
      Alpha = 0.5f // Green
    }
  };

// Create general placement properties for Standard engine

//CIMStandardGeneralPlacementProperties generalPlacementProperties =
//  new CIMStandardGeneralPlacementProperties
//  {
//    DrawUnplacedLabels = true,
//    InvertedLabelTolerance = 3.0,
//    RotateLabelWithDisplay = true,
//    UnplacedLabelColor = new CIMRGBColor
//    {
//      R = 255, G = 0, B = 0, Alpha = 0.5f // Red
//    } 
//   };


// Create annotation  label classes
// Green label
CIMLabelClass greenLabelClass = new CIMLabelClass
{
  Name = "Green",
  ExpressionTitle = "Expression-Green",
  ExpressionEngine = LabelExpressionEngine.Arcade,
  Expression = "$feature.OBJECTID",
  ID = 1,
  Priority = 0,
  Visibility = true,
  TextSymbol = new CIMSymbolReference
  {
    Symbol = new CIMTextSymbol()
    {
      Angle = 45,
      FontType = FontType.Type1,
      FontFamilyName = "Tahoma",
      FontEffects = FontEffects.Normal,
      HaloSize = 2.0,

      Symbol = new CIMPolygonSymbol
      {
        SymbolLayers = new CIMSymbolLayer[]
        {
          new CIMSolidFill
          {
            Color = CIMColor.CreateRGBColor(0, 255, 0)
          }
        },
        UseRealWorldSymbolSizes = true
      }
    },
    MaxScale = 0,
    MinScale = 0,
    SymbolName = "TextSymbol-Green"
  },
  StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
  {
    AllowOverlappingLabels = true,
    LineOffset = 1.0
  },
  MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
  {
    AlignLabelToLineDirection = true,
    AvoidPolygonHoles = true
  }
};

// Blue label
CIMLabelClass blueLabelClass = new CIMLabelClass
{
  Name = "Blue",
  ExpressionTitle = "Expression-Blue",
  ExpressionEngine = LabelExpressionEngine.Arcade,
  Expression = "$feature.OBJECTID",
  ID = 2,
  Priority = 0,
  Visibility = true,
  TextSymbol = new CIMSymbolReference
  {
    Symbol = new CIMTextSymbol()
    {
      Angle = 45,
      FontType = FontType.Type1,
      FontFamilyName = "Consolas",
      FontEffects = FontEffects.Normal,
      HaloSize = 2.0,

      Symbol = new CIMPolygonSymbol
      {
        SymbolLayers = new CIMSymbolLayer[]
        {
          new CIMSolidFill
          {
            Color = CIMColor.CreateRGBColor(0, 0, 255)
          }
        },
        UseRealWorldSymbolSizes = true
      }
    },
    MaxScale = 0,
    MinScale = 0,
    SymbolName = "TextSymbol-Blue"
  },
  StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
  {
    AllowOverlappingLabels = true,
    LineOffset = 1.0
  },
  MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
  {
    AlignLabelToLineDirection = true,
    AvoidPolygonHoles = true
  }
};

// Create a list of labels
List<CIMLabelClass> labelClasses = new List<CIMLabelClass> { greenLabelClass, blueLabelClass };

// Create an annotation feature class description object to describe the feature class to create
AnnotationFeatureClassDescription annotationFeatureClassDescription =
  new AnnotationFeatureClassDescription(annotationFeatureClassName, fieldDescriptions, shapeDescription,
    generalPlacementProperties, labelClasses)
  {
    IsAutoCreate = true,
    IsSymbolIDRequired = false,
    IsUpdatedOnShapeChange = true
  };

// Create a SchemaBuilder object
SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Add the creation of the Cities annotation feature class to the list of DDL tasks
schemaBuilder.Create(annotationFeatureClassDescription);

// Execute the DDL
bool success = schemaBuilder.Build();

// Inspect error messages
if (!success)
{
  IReadOnlyList<string> errorMessages = schemaBuilder.ErrorMessages;
  //etc.
}

// Creating a feature-linked annotation feature class between water pipe and valve in water distribution network
// with following user defined fields
// PipeName 
// GlobalID

// Annotation feature class name
string annotationFeatureClassName = "WaterPipeAnnotation";

// Create user defined attribute fields for annotation feature class
FieldDescription pipeGlobalID = FieldDescription.CreateGlobalIDField();
FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 255);

// Create a list of all field descriptions
List<FieldDescription> fieldDescriptions = new List<FieldDescription> { pipeGlobalID, nameFieldDescription };

// Create a ShapeDescription object
ShapeDescription shapeDescription = new ShapeDescription(GeometryType.Polygon, spatialReference);

// Create general placement properties for Maplex engine 
CIMMaplexGeneralPlacementProperties generalPlacementProperties = new CIMMaplexGeneralPlacementProperties
{
  AllowBorderOverlap = true,
  PlacementQuality = MaplexQualityType.High,
  DrawUnplacedLabels = true,
  InvertedLabelTolerance = 1.0,
  RotateLabelWithDisplay = true,
  UnplacedLabelColor = new CIMRGBColor
  {
    R = 255,
    G = 0,
    B = 0,
    Alpha = 0.5f
  }
};

// Create annotation  label classes
// Green label
CIMLabelClass greenLabelClass = new CIMLabelClass
{
  Name = "Green",
  ExpressionTitle = "Expression-Green",
  ExpressionEngine = LabelExpressionEngine.Arcade,
  Expression = "$feature.OBJECTID",
  ID = 1,
  Priority = 0,
  Visibility = true,
  TextSymbol = new CIMSymbolReference
  {
    Symbol = new CIMTextSymbol()
    {
      Angle = 45,
      FontType = FontType.Type1,
      FontFamilyName = "Tahoma",
      FontEffects = FontEffects.Normal,
      HaloSize = 2.0,

      Symbol = new CIMPolygonSymbol
      {
        SymbolLayers = new CIMSymbolLayer[]
        {
          new CIMSolidFill
          {
            Color = CIMColor.CreateRGBColor(0, 255, 0)
          }
        },
        UseRealWorldSymbolSizes = true
      }
    },
    MaxScale = 0,
    MinScale = 0,
    SymbolName = "TextSymbol-Green"
  },
  StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
  {
    AllowOverlappingLabels = true,
    LineOffset = 1.0
  },
  MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
  {
    AlignLabelToLineDirection = true,
    AvoidPolygonHoles = true
  }
};

// Blue label
CIMLabelClass blueLabelClass = new CIMLabelClass
{
  Name = "Blue",
  ExpressionTitle = "Expression-Blue",
  ExpressionEngine = LabelExpressionEngine.Arcade,
  Expression = "$feature.OBJECTID",
  ID = 2,
  Priority = 0,
  Visibility = true,
  TextSymbol = new CIMSymbolReference
  {
    Symbol = new CIMTextSymbol()
    {
      Angle = 45,
      FontType = FontType.Type1,
      FontFamilyName = "Consolas",
      FontEffects = FontEffects.Normal,
      HaloSize = 2.0,

      Symbol = new CIMPolygonSymbol
      {
        SymbolLayers = new CIMSymbolLayer[]
        {
          new CIMSolidFill
          {
            Color = CIMColor.CreateRGBColor(0, 0, 255)
          }
        },
        UseRealWorldSymbolSizes = true
      }
    },
    MaxScale = 0,
    MinScale = 0,
    SymbolName = "TextSymbol-Blue"
  },
  StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
  {
    AllowOverlappingLabels = true,
    LineOffset = 1.0
  },
  MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
  {
    AlignLabelToLineDirection = true,
    AvoidPolygonHoles = true
  }
};

// Create a list of labels
List<CIMLabelClass> labelClasses = new List<CIMLabelClass> { greenLabelClass, blueLabelClass };


// Create linked feature description
// Linked feature class name
string linkedFeatureClassName = "WaterPipe";

// Create fields for water pipe
FieldDescription waterPipeGlobalID = FieldDescription.CreateGlobalIDField();
FieldDescription pipeName = FieldDescription.CreateStringField("PipeName", 255);

// Create a list of water pipe field descriptions
List<FieldDescription> pipeFieldDescriptions = new List<FieldDescription> { waterPipeGlobalID, pipeName };

// Create a linked feature class description
FeatureClassDescription linkedFeatureClassDescription = new FeatureClassDescription(linkedFeatureClassName, pipeFieldDescriptions,
  new ShapeDescription(GeometryType.Polyline, spatialReference));

// Create a SchemaBuilder object
SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Add the creation of the linked feature class to the list of DDL tasks
FeatureClassToken linkedFeatureClassToken = schemaBuilder.Create(linkedFeatureClassDescription);

// Create an annotation feature class description object to describe the feature class to create
AnnotationFeatureClassDescription annotationFeatureClassDescription =
  new AnnotationFeatureClassDescription(annotationFeatureClassName, fieldDescriptions, shapeDescription,
    generalPlacementProperties, labelClasses, new FeatureClassDescription(linkedFeatureClassToken))
  {
    IsAutoCreate = true,
    IsSymbolIDRequired = false,
    IsUpdatedOnShapeChange = true
  };

// Add the creation of the annotation feature class to the list of DDL tasks
schemaBuilder.Create(annotationFeatureClassDescription);

// Execute the DDL
bool success = schemaBuilder.Build();

// Inspect error messages
if (!success)
{
  IReadOnlyList<string> errorMessages = schemaBuilder.ErrorMessages;
  //etc.
}

var lyr = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>().FirstOrDefault(f => f.ShapeType == esriGeometryType.esriGeometryPolygon);
if (lyr == null) return;
QueuedTask.Run(() =>
{
  //Get the layer's definition
  //community sample Data\Admin\AdminSample.aprx
  var lyrDefn = lyr.GetDefinition() as CIMFeatureLayer;
  if (lyrDefn == null) return;
  //Get the label classes - we need the first one
  var listLabelClasses = lyrDefn.LabelClasses.ToList();
  var theLabelClass = listLabelClasses.FirstOrDefault();
  //set the label class Expression to use the Arcade expression
  theLabelClass.Expression = "return $feature.STATE_NAME + TextFormatting.NewLine + $feature.POP2000;";
  //Set the label definition back to the layer.
  lyr.SetDefinition(lyrDefn);
});

//Note: call within QueuedTask.Run()

//Get the layer's definition
var lyrDefn = featureLayer.GetDefinition() as CIMFeatureLayer;
//Get the label classes - we need the first one
var listLabelClasses = lyrDefn.LabelClasses.ToList();
var theLabelClass = listLabelClasses.FirstOrDefault();
//Set the label classes' symbol to the custom text symbol
//Refer to the ProSnippets-TextSymbols wiki page for help with creating custom text symbols.
//Example: var textSymbol = await CreateTextSymbolWithHaloAsync();
theLabelClass.TextSymbol.Symbol = textSymbol;
lyrDefn.LabelClasses = listLabelClasses.ToArray(); //Set the labelClasses back
featureLayer.SetDefinition(lyrDefn); //set the layer's definition
                                     //set the label's visiblity
featureLayer.SetLabelVisibility(true);

//Note: call within QueuedTask.Run()

//Get the layer's definition
var lyrDefn = featureLayer.GetDefinition() as CIMFeatureLayer;
//Get the label classes - we need the first one
var listLabelClasses = lyrDefn.LabelClasses.ToList();
var theLabelClass = listLabelClasses.FirstOrDefault();

//Modify label Placement 
//Check if the label engine is Maplex or standard.
CIMGeneralPlacementProperties labelEngine = 
   MapView.Active.Map.GetDefinition().GeneralPlacementProperties;
if (labelEngine is CIMStandardGeneralPlacementProperties) //Current labeling engine is Standard labeling engine               
  theLabelClass.StandardLabelPlacementProperties.PointPlacementMethod = 
           StandardPointPlacementMethod.OnTopPoint;
else    //Current labeling engine is Maplex labeling engine            
  theLabelClass.MaplexLabelPlacementProperties.PointPlacementMethod = 
          MaplexPointPlacementMethod.CenteredOnPoint;

lyrDefn.LabelClasses = listLabelClasses.ToArray(); //Set the labelClasses back
featureLayer.SetDefinition(lyrDefn); //set the layer's definition