It’s official, folks: Windows 10 will be a free upgrade for existing Windows users—as long as you claim it quickly.

Kicking off the consumer-focused Windows 10 event in Redmond on Tuesday, January 21, Microsoft operating system chief Terry Myerson announced that current users of Windows 7, Windows 8.1, and Windows Phone 8.1 will be able to upgrade to the new operating system for free as long as they do so within one year of Windows 10's July 29 launch. Once you’ve claimed the upgrade, it's permanent, and Microsoft will keep you updated for the supported lifetime of the device.

“We think of Windows 10 as a service,” Myerson said.

Here's the fine print from the Windows 10 page on Microsoft's site:

“It is our intent that most of these devices will qualify, but some hardware/software requirements apply and feature availability may vary by device. Devices must be connected to the internet and have Windows Update enabled. ISP fees may apply. Windows 7 SP1 and Windows 8.1 Update required. Some editions are excluded: Windows 7 Enterprise, Windows 8/8.1 Enterprise, and Windows RT/RT 8.1. Active Software Assurance customers in volume licensing have the benefit to upgrade to Windows 10 Enterprise outside of this offer. We will be sharing more information and additional offer terms in coming months.”

Did you catch that? Windows RT tablets won't be upgraded to Windows 10—though they'll get some of the new features—and business users will have to pay to upgrade and receive continued support.

The decision to make Windows 10 a free upgrade for existing users makes sense. Windows 8 users have vocally expressed their displeasure with the operating system, prompting happy Windows 7 users to stay put on that OS. That hinders Microsoft's ability to execute its vision for a service-centric, cloud-connected future for Windows; making Windows 10 free could spur more users into embracing a modern Microsoft operating system.

And hey, it'd be weird to charge for Windows 10 after Windows 8 flopped so hard and Apple started giving away OS upgrades. Right?

This article originally published on January 21, 2015, but was updated March 18, June 1, and July 29, 2015 with additional information.