Apple has been quietly rolling out iTunes Match audio fingerprint to all Apple Music subscribers. Previously Apple was using a less accurate metadata version of iTunes Match on Apple Music, which wouldn’t always match the correct version of a particular song. We’ve all seen the stories of a live version of a song being replaced by a studio version, etc.
iTunes Match with audio fingerprint should make for much more accurate matching. If you had songs that were incorrectly matched, the new version will rematch the correct song but it won't delete downloaded copies of songs you have in your library.
The feature is now the same as the version of iTunes Match that you can pay for as a separate service. So if you currently subscribe to iTunes Match, you can subscribe to Apple Music then let your iTunes Match subscription expire and continue to receive the same benefits.
Apple is reportedly switching over 1% to 2% of its users every day, automatically. Apple Music subscribers will see "Matched" in the iCloud Status column of iTunes for Mac when the service has been gone active on their account.