The last few updates for Windows 10 Technical Preview were delivered directly from Windows Update for customers registered in the Windows Insiders program, but it looks like the next update will be available as an ISO at launch.
That's according to Gabriel Aul, head of the Windows Insider program:
@NaThanPhamIT Next build we release will include ISOs as well as published via Windows Update to upgrade existing installs.— Gabriel Aul (@GabeAul) January 5, 2015
ISOs of previous builds were made available eventually, but they usually came a few weeks after the the update was delivered through Windows Update. For the upcoming build, it looks like the ISO will be available at the same time as Windows Update.
As for when the next update is set to arrive, Microsoft is holding a Windows 10 event on January 21, which is when we'll likely hear more details about the upcoming OS. There have been indications suggesting that the next build will be a consumer preview, with features like Cortana for desktop and more. We'll have more details to share on January 21.
Until then, what are your thoughts on Windows 10?