Web.UIVersion property

Gets or sets the user interface (UI) version of the Web site.

Namespace:  Microsoft.SharePoint.Client
Assembly:  Microsoft.SharePoint.Client (in Microsoft.SharePoint.Client.dll)

public int UIVersion { get; set; }

Property value

Type: System.Int32
A 32-bit integer between 0 and 127 that specifies the UI version.

The UI version defines the UI elements and master pages that are used on the Web, and is used to determine compatibility with other SharePoint Server components.