Unless it was a very innocuous update, release notes can always be found here a couple hours or so after the update:
https://www.sonos.com/en-us/support
Scroll down to "Documentation" on the right.
For 10.3, here are the notes:
Current software version
10.3
In this update:
- We’ve made improvements to the More Info view for Podcast episodes in the Sonos app. Podcasts will now appear in Recent Searches and Recently Played.
- Sonos products now work with Control4’s Simple Device Discovery Protocol (SDDP).
System requirements
- Android 5.0 or later
- iOS 10 or later
- macOS 10.11 or later
- Windows 7 or later