One of the innovations in Mac OS Sierra 10.12.4 is a new version of Safari, but the fact is that the update is also available to Yosemite (10.10) and El Capitan (10.11).
This is news listed for Safari 10.1:
- Provides the ability to pull the "View downloads" into a standalone window
- Adds "paste and surf" from the context menu in Safari smart search field
- fixes an issue with background tabs that suddenly appears in the foreground
- Various security fixes, details of these are available on Apple's website