ArcGIS Pro 2.8 API Reference Guide
Length Property (CubicBezierSegment)
Example 

ArcGIS.Core.Geometry Namespace > CubicBezierSegment Class : Length Property
Gets the 2D length of the cubic bezier.
Syntax
public override double Length {get;}
Public Overrides NotOverridable ReadOnly Property Length As Double
Remarks
If the 3D length of the cubic bezier is required, create a polyline from the bezier segment and use the Polyline.Length3D property.
Example
// retrieve the bezier curve's control points
CubicBezierSegment cb = CubicBezierBuilder.CreateCubicBezierSegment(bezierSegment);
MapPoint startPt = cb.StartPoint;
Coordinate2D ctrlPt1 = cb.ControlPoint1;
Coordinate2D ctrlPt2 = cb.ControlPoint2;
MapPoint endPt = cb.EndPoint;

bool isCurve = cb.IsCurve;
double len = cb.Length;
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

CubicBezierSegment Class
CubicBezierSegment Members