https://arstechnica.com/gadgets/2017/09/apples-macos-high-sierra-golden-master-is-available-to-devs-today/

The golden master (GM) candidate of macOS High Sierra was released to developers today. The GM doesn't add any significant new features over the previous beta version, but it can be helpful for QAing Mac software updates for High Sierra before the public roll-out, as minimal changes are expected between this seed and September 25's public release.

In general, High Sierra is a significant update under the hood, but it's light on highly visible changes for general users. We're looking at quality-of-life stuff and foundations for future developments. That doesn't mean there's nothing for Mac app and game developers to dive into, though. Features of the final version of High Sierra include a new proprietary file system, HEVC video support, the Metal 2 graphics API, and myriad tweaks to various apps and services. It will be the first update to macOS since 10.12.6 on July 19.