How to Clean Install and Activate Windows 10 Without Upgrading First

Update

Microsoft made activation easier. The following info works for Windows 10 version 1511 or higher.

We have received a lot of feedback from Insiders on making it easier to activate Windows 10 on devices that take advantage of the free upgrade offer to genuine Windows by using existing Windows 7, Windows 8 or Windows 8.1 product keys. If you install this build of the Windows 10 Insider Preview on a PC and it doesn’t automatically activate, you can enter the product key from Windows 7, Windows 8 or Windows 8.1 used to activate the prior Windows version on the same device to activate Windows 10 by going to Settings > Update & security > Activation and selecting Change Product Key.If you do a clean install of Windows 10 by booting off the media, you can also enter the product key from prior Windows versions on qualifying devices during setup.

- Source: Microsoft Blog

Original article follows

As you know, Windows 10 comes free if you upgrade from Windows 7, 8, 8.1 by 29 July 2016. This free offer works well when upgrading from within Windows 7 or 8/8.1 but if you do a regular clean install of Windows 10, the resulting OS will not be activated with your existing Windows 7/8 license key. We explained this "fingerprinting" process in detail here.

In this tutorial we'll show you how to bypass this limitation and do a clean Win 10 install, then activate it with your existing Windows 7/8/8.1 license key. It's a very useful method for advanced users wishing to perform a clean install and skip the upgrade process.

Note: This method only works if you can access your current Windows 7 or 8/8.1 OS, as you will need to perform steps 1 to 5 from within it, in order to create an activation file for Windows 10.

Here is the step-by-step guide:

Make sure you do a backup first.

1. Download the Windows 10 ISO file.

Note that the ISO you download should match the architecture of your current OS. Basically if your Windows 7 or 8 is 32-bit, download a 32-bit Windows 10 ISO file. If you're running a 64-bit Win 7/8, then you must download a Win 10 64-bit ISO file. This guide should come in handy: Find out if your Windows is 32-bit or 64-bit - guide for XP, Vista, 7, 8, 8.1, 10.

2. Mount or extract the ISO file downloaded in step 1.

In Windows 8 and 8.1, you can simply right-click the ISO file and choose Mount. If you don't see a Mount option, here's how to re-enable ISO Mounting in File Explorer under Win 8/8.1.

3. Browse the previously mounted or extracted ISO file and navigate to the folder sources and copy/paste the file gatherosstate.exe to your Desktop (or you can drag&drop it to Desktop).

4. Run gatherosstate.exe and notice that it creates GenuineTicket.xml on your desktop.

5. Copy GenuineTicket.xml to a safe location outside the partition on which you plan to install Windows 10 on. For instance, you can copy GenuineTicket.xml to a USB stick or upload it to a cloud drive so you can retrieve it later on.

6. Do a clean install of Windows 10 on your PC (in the linked tutorial, go with method 2 or 3 in order to use the ISO you just downloaded in step 1 here; method 1 re-downloads the setup files all over again). Skip the product key activation checks all the way to the end.

7. After you are booted into Windows 10, copy the file GenuineTicket.xml to C:\ProgramData\Microsoft\Windows\ClipSVC\GenuineTicket, assuming C is your Windows 10 partition.

The folder ClipSVC is hidden by default, so you need to see hidden files, folders, and drives. Basically, in File Explorer, switch to the "View" tab and check the box "Hidden items".

8. Reboot the PC.

That's it. Your Windows 10 should now be activated. You can check activation by going to Start > Settings > Update & security > Activation. Or you can press the Win key + Pause.

- via Reddit.