The upcoming Windows Blue update, now officially known as Windows 8.1, will be delivered as a free update through the operating system’s app store, Microsoft confirmed today.

Redmond’s chief marketing officer, Tami Reller, appeared at JP Morgan’s Technology, Media and Telecom Conference in Boston this morning, where she said Windows 8.1 will be delivered free to Windows 8 and Windows RT users.

The update will be “easy to get from the Windows start screen through the app store,” Reller said. “This means that customers today who have Windows 8 or plan to buy a device in the near future can seamlessly get the advantages of Windows 8.1”

Reller declined to provide an exact release date for Windows 8.1, but said that Microsoft is “very sensitive to the timing of the holidays.”

Ideally, Microsoft will be able to provide devices with Windows 8.1 pre-loaded in time for the holiday 2013 season, Reller said, but those who purchase a Windows 8 device later this year will be able to easily upgrade to 8.1.

Word of Windows 8.1 first emerged in March with leaked screenshots that showed off some of the changes Microsoft had in mind for Windows 8. Redmond acknowledged Windows Blue a few days later, and promised more details at its June Build conference. Microsoft will, in fact, release a public preview of Windows 8.1 at Build. After June 26, the “preview will be available for anyone to download,” Reller said today.

The leak suggested that Microsoft will be expanding the allowable size of tiles that one can place on Windows 8’s Start Screen, and adding customization options, among other things. Microsoft is also reportedly bringing back the start button.

Earlier this month, Reller said Windows 8.1 “will deliver the latest new innovations across an increasingly broad array of form factors of all sizes, display, battery life and performance, while creating new opportunities for our ecosystem. It will provide more options for businesses, and give consumers more options for work and play.”

While Microsoft has been rolling out small updates via Windows Update since the October launch of Windows 8, Windows 8.1 will be “more substantial” than anything Redmond could deliver via daily or weekly updates, Reller said today. “We also wanted to make it very, very easy for customers to consume.”

Windows 8 users will get a notification when Windows 8.1 is live.

For more, see PCMag’s review of Windows 8, as well as What Is Windows Blue?