[hoffs]

How would you know in the first place

[kasabali]

apt shows the NEWS file during update when there's a change.

If it doesn't (ie. you set it up to blindly do the upgrade), you can still check the news file or .debian.changelog.gz file afterwards.

Lastly, when it's shipped in the new major Debian stable release in a few years, it'll surely be noted in the release notes.