In other words, if you have a Lumia 930, 1520, 830 or whatever - everything except the Lumia 635, according to Microsoft, see the updated post here, then you can play with THE latest build of Windows 10 Mobile, right up on the 'top branch' and bleeding edge everything. Which is very cool, especially as some of the compatible phones are up to 3 years old now.
As usual, head into the Windows Insider application and choose the 'Fast' ring and then follow the instructions.
You can upgrade in-place, but a word of warning - when I did this on my 950 XL, the resulting OS wasn't fully stable and battery life was appalling. After a hard reset, all was well - in fact, smoother and more efficient than the current 'Threshold' branch. So be warned, you might need to backup and then restore or - in worst case - set up as a new device and then resync data and reinstall applications. But hey, they don't call it the bleeding edge for nothing!
Your comments welcome.