Unless a significant issue is found, macOS High Sierra 10.13 GM candidate (17A362a) will likely be the last release before the September 25th launch.
Both releases are likely golden master candidates, though Apple hasn’t specifically stated that.
Friday’s release accelerates an already accelerated release cycle, as the last round of developer betas hit just four days ago.
Thursday’s release accelerates an already accelerated release cycle, as the last developer beta for tvOS 11 hit on Monday of this week.
Apple has the pedal to the metal on iOS 11, as it released the second developer beta in a week: iOS 11 Developer Beta 9 (15A5370a).
This is a major expansion from the 2,000 beta testers that were previously allowed through TestFlight.