Will Windows 10 free upgrade expire after one year

Windows 10 will be free for the first year to all Windows 7, Windows 8.1 and Phone 8.1 users.

Wow, thats cool, but does that mean, I will have to pay for Windows 10 after the first year?

No. Its a promotion to get as many users to upgrade their existing Windows 7 PCs and Windows 8.1 devices to Windows 10. Once you upgrade within the first year for free, its yours forever at no additional cost. As Microsoft Program Manager for Windows Terry Myerson described it:

This is more than a one-time upgrade: once a Windows device is upgraded to Windows 10, we will continue to keep it current for the supported lifetime of the device –at no additional charge.

Source: http://blogs.windows.com/bloggingwindows/2015/01/21/the-next-generation-of-windows-windows-10/

I heard Microsoft representatives mention they are moving to a servicing model for Windows 10, does that mean Windows 10 is going to require a subscription?

No, Windows 10 remains a perpetual license, which means, you can upgrade to Windows 10 and use it forever without it expiring or going into any reduced functional mode.

Are you saying there will be no more versions of Windows after Windows 10?

Microsoft is moving Windows to a servicing model with Windows 10. The days of major revisions or what are called big bang releases are no more. As Microsoft Program Manager for Windows Terry Myerson described it:

This is more than a one-time upgrade: once a Windows device is upgraded to Windows 10, we will continue to keep it current for the supported lifetime of the device – at no additional charge. With Windows 10, the experience will evolve and get even better over time. We’ll deliver new features when they’re ready, not waiting for the next major release. We think of Windows as a Service – in fact, one could reasonably think of Windows in the next couple of years as one of the largest Internet services on the planet.

And just like any Internet service, the idea of asking "What version are you on?" will cease to make sense – which is great news for our Windows developers.

Source: http://blogs.windows.com/bloggingwindows/2015/01/21/the-next-generation-of-windows-windows-10/

Why is Windows 10 free, is there some catch?

No, its not a catch. We are computing in different times. Windows 10 is free so app developers can standardize on one platform and reduce the fragmented market of different versions and editions of Windows that have been an issue in the past. When everybody is on the same platform, it means better quality apps, a healthier ecosystem and more advances in hardware and software innovation.