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Windows 10 Tech Preview full .iso download is now available. Note that you may need to be signed into Windows Insider Program. You can use an existing Windows Mail account such as Outlook.com, Live.com, etc.
Also note that this is a preview, not release candidate, primarily orientated toward techies. It may contain glitches and other faults that could effect its usability. You should also install it in an isolated manner to protect your current OS.