Last week Microsoft released Windows 10 Build 10586 to Windows Insiders on the Fast Ring for testing and today that same build has been made available to those Insiders on the Slow Ring.
This is a strong indication that Microsoft has continued to test this build, reviewed the telemetry since it was sent out to Fast Ring Insiders last week and believes it is stable enough for Insiders who choose not to be on the bleeding edge of Windows 10 builds.
A Windows 10 build that is released to the Insider's Slow Ring normally means the ISO will also be made available for download so that clean installs can be accomplished. However, according to Gabe Aul, it may still be a couple of days before the ISO is available on the Windows Insider site for download.
The next big question is whether or not Windows 10 Build 10586 is going to materialize as the final build off the Threshold 2 (TH2) branch and be the expected November update.
Insiders have been testing various builds from the TH2 branch since Windows 10 was released in late July and eventually one of these builds will become the next significant update to Windows 10.
Windows 10 Build 10586 appears to be the on deck candidate.