https://www.theverge.com/2018/6/27/17510344/microsoft-windows-10-tabs-sets-feature-update-removal

Microsoft isn’t planning to ship its tabbed app feature, dubbed Sets, with the next major Windows 10 update later this year. Sources familiar with Microsoft’s plans tell The Verge that the company is aiming to tweak and improve the tabs integration in apps like Edge and Microsoft Office before they’re broadly available in Windows 10. Windows Insiders have been able to test the Sets feature over the past six months, providing feedback on the changes.

That feedback has led Microsoft to remove Sets from its latest Windows 10 test build, 17704, which is being released today. Sets will return for insiders once Microsoft starts testing its next major Windows 10 update sometime in the coming months. “Some of the things we’re focusing on include improvements to the visual design and continuing to better integrate Office and Microsoft Edge into Sets to enhance workflow,” explains Microsoft’s Dona Sarkar.