The TabGroupPane within a DocumentContentHost uses a custom template (keyed by TabGroupPane.DocumentTabGroupTemplateKey). You can retemplate this element as needed - we ship the default xaml for the elements in the DefaultStyles directory. That default template uses a custom panel for the itemspanel so to do what you want you would likely need to use a different panel - perhaps even our TabItemPanel with a TabLayoutStyle of SingleRowSizeToFit. Note, the DocumentTabPanel is a custom panel does not require/support scrolling so the template we provide doesn't have any scrolling elements so your custom template would probably need to add some. Also, this panel provides an attached property that the DocumentFilesMenuItem uses to trigger off whether to indicate there are items out of view (i.e. whether the bar is rendered above the dropdown arrow in that menu item) so that would not work if you use a different panel.