public sealed class AnnotationFeatureClassDefinition : ArcGIS.Core.Data.FeatureClassDefinition, System.IDisposable  

// get an anno layer
AnnotationLayer annoLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<AnnotationLayer>().FirstOrDefault();
if (annoLayer == null)
  return;

QueuedTask.Run(() =>
{
  Inspector insp = null;
  // get the anno feature class
  var fc = annoLayer.GetFeatureClass() as ArcGIS.Core.Data.Mapping.AnnotationFeatureClass;

  // get the featureclass CIM definition which contains the labels, symbols
  var cimDefinition = fc.GetDefinition() as ArcGIS.Core.Data.Mapping.AnnotationFeatureClassDefinition;
  var labels = cimDefinition.GetLabelClassCollection();
  var symbols = cimDefinition.GetSymbolCollection();

  // make sure there are labels, symbols
  if ((labels.Count == 0) || (symbols.Count == 0))
    return;

  // find the label class required
  //   typically you would use a subtype name or some other characteristic
  // in this case lets just use the first one

  var label = labels[0];

  // each label has a textSymbol
  // the symbolName *should* be the symbolID to be used
  var symbolName = label.TextSymbol.SymbolName;
  int symbolID = -1;
  if (!int.TryParse(symbolName, out symbolID))
  {
    // int.TryParse fails - attempt to find the symbolName in the symbol collection
    foreach (var symbol in symbols)
    {
      if (symbol.Name == symbolName)
      {
        symbolID = symbol.ID;
        break;
      }
    }
  }
  // no symbol?
  if (symbolID == -1)
    return;

  // load the schema
  insp = new Inspector();
  insp.LoadSchema(annoLayer);

  // ok to assign these fields using the inspector[fieldName] methodology
  //   these fields are guaranteed to exist in the annotation schema
  insp["AnnotationClassID"] = label.ID;
  insp["SymbolID"] = symbolID;

  // set up some additional annotation properties
  AnnotationProperties annoProperties = insp.GetAnnotationProperties();
  annoProperties.FontSize = 36;
  annoProperties.TextString = "My Annotation feature";
  annoProperties.VerticalAlignment = VerticalAlignment.Top;
  annoProperties.HorizontalAlignment = HorizontalAlignment.Justify;

  insp.SetAnnotationProperties(annoProperties);

  var tags = new[] { "Annotation", "tag1", "tag2" };

  // use daml-id rather than guid
  string defaultTool = "esri_editing_SketchStraightAnnoTool";

  // tool filter is the tools to filter OUT
  var toolFilter = new[] { "esri_editing_SketchCurvedAnnoTool" };

  // create a new template 
  var newTemplate = annoLayer.CreateTemplate("new anno template", "description", insp, defaultTool, tags, toolFilter);
});

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();
    }
  });
}