Windows 10 upgrade is free for Windows 7, 8.1 and Phone 8.1 users for one year (update)

Microsoft will offer a free upgrade to Windows 10 for one year after the operating system's launch to existing users of Windows 7, Windows 8.1 and Windows Phone 8.1, the company announced today.

"Once a device is upgraded to Windows 10, we'll be keeping it current for the supported lifetime for the device," said Terry Myerson, chief of Microsoft's operating systems division. Myerson described a shift to Windows as a service starting with Windows 10, referring to the new operating system as "one of the largest internet services on the planet."

Windows 10 is set to launch later this year. Microsoft has previously offered limited-time promotions on operating system upgrades, such as a discounted upgrade to Windows 8 for $39.99 through January 2013. Apple has delivered free OS X upgrades for years.

Update: In a Q&A with press following the event, Microsoft CEO Satya Nadella clarified that Microsoft's vision for Windows as a service doesn't mean the company is changing its business model for Windows to a plan with an annual fee, or any kind of subscription.

All customers running Windows 7, Windows 8.1 and Windows Phone 8.1 will be able to upgrade to Windows 10 for free within a one-year period following the operating system's launch later this year. After that period, users will have to pay for the upgrade as they would have with previous versions of Windows. Those who get the upgrade during the free period will have Windows 10 on their device permanently.