Safari Technology Preview, an experimental version of the Safari browser meant for testing upcoming new capabilities and web technologies, is a good place to look for clues regarding new features in development. Today, Apple released an eighth update to Safari Technology Preview, which debuted in March 2016, and the browser appears to include pieces of code to support the upcoming Apple Pay integration with websites.
According to the official release notes on Apple’s website, several pieces of supporting Apple Pay code have been moved to the open-source repository. Apple Pay for websites was announced at WWDC 2016 as a new feature in Safari 10 which will ship as part of the free macOS Sierra software update this fall.
If you previously downloaded the browser, the new version should appear in the Mac App Store’s Updates tab. The Safari Technology Preview update is available for download from Apple.