Safari Technology Preview release 47 includes bug fixes and feature improvements with an experimental implementation of the Storage Access API, updates to Service Workers, and improvements to Media, Rendering, Web Inspector, and the Clipboard API.
Today's update also includes mitigations for the Spectre hardware vulnerability that impacts Apple's Macs. Spectre fixes were previously added to the release version of Safari with yesterday's release of a supplemental update macOS High Sierra 10.13.2.
The Safari Technology Preview update is available through the Software Update mechanism in the Mac App Store to anyone who has downloaded the browser. Full release notes for the update are available on the Safari Technology Preview website.
Apple's aim with Safari Technology Preview is to gather feedback from developers and users on its browser development process. Safari Technology Preview can run side-by-side with the existing Safari browser and while designed for developers, it does not require a developer account to download.