Well, this is different: Microsoft has made the most recent Windows 10 Insider Preview build for Fast ring testers, build 10130, available as an ISO download. But unlike in the past, this milestone doesn’t also include the release of 10130 to Slow ring testers. Not yet, anyway. Microsoft says it needs a bit more time in the oven.
The “oven” in this case means that Microsoft will deliver a few more bug fixes for build 10130 before releasing the build to Slow ring testers. Which is the typical approach: before it will OK a Windows Insider build for Slow ring installs, Microsoft checks the reliability of that build with Fast ring tester telemetry and ships bug fixes as needed.
What’s new, of course, is the release of an ISO—which enables clean installs of the OS—before a build ships to the Slow ring release. Previously, these two things have always happened simultaneously. (That said, I never understood why Microsoft didn’t simply release ISOs at the time a Fast ring build appeared. The types of testers who can handle the Fast ring are also the types of people who would want an ISO.)
But there’s a reason for this release, and sadly this appears to be a one-time exception.
“We’re making a special exception today,” a Microsoft blog post confirms. “We know that a bunch of Windows Insiders on the Fast ring are currently blocked getting to the latest build due a 0x80146017 error. With the ISOs, they can mount the image and upgrade directly from the ISO and get unblocked.”
Or you could do a clean install. Which, frankly, is better for you, and better for useful testing telemetry. (Beta build upgrades over previous beta builds are pretty worthless, in my opinion.)