Create Multi-line Tabs
Multi-line tabs can be created using the IsBreak property of the RadTabItem. The property is of Boolean type and the possible values are True or False. If it’s True, then the next tab items you add will be placed on a new line inserted right above the item which property IsBreak is set to True; if it’s False, no break is inserted.
<telerik:RadTabControl x:Name="radTabControl" SelectedIndex="0">
<telerik:RadTabItem Header="Calendar"/>
<telerik:RadTabItem Header="Colors" IsBreak="True"/>
<telerik:RadTabItem Header="Quote"/>
</telerik:RadTabControl>
In the above example the property IsBreak of the tab item "Colors" is set to True and the next tab item "Quote" is placed on a new line above all other tab items.