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Windows 10 is the latest version of Windows. It was released in July 2015 and till now different build versions of Windows 10 has been released. We have been releasing new feature updates twice a year. Currently, the latest version of Windows 10 is
1809. You can say that Windows 10 will be supported for lifetime, as we have not planned to release a new version of Windows. Therefore, we will be providing updates and support for Windows 10.
The availability of Windows 10 and end of service dates are segmented by build versions. For more information on the support for Windows 10 build versions, you can refer the article
Windows lifecycle fact sheet.
If you want to upgrade to Windows 10 you can purchase it from Microsoft Store.