Usually when Microsoft launch a new flavour of Windows the previous version is available preinstalled on new machines for at least another two years. It’s different with Windows 10!
Windows 7 Professional will be available until 31 October 2016 (4 years after the launch of Windows 8) while Windows 8.1 will also be available until 31 October 2016 but that’s a mere 15 months after the launch of Windows 10.
The end of Windows 8 comes even quicker at 30 June 2016. Microsoft’s Windows lifecycle fact sheet has all the details: http://bit.ly/1MGslQR.