According to a fresh report coming from Slashgear, Apple Music will stream 256kbps files which is the same aswith Apple's current iTunes Match product. At the moment, Apple's existing Beats Music streams MP3 files to desktops and mobile devices at 320kbps on the high end.
There's also the option to save up data and stream at a standard quality of 64kbps using the HE-AAC codec. To put this into perspective, Spotify offers three bitrates using the Ogg Vorbis format - the normal mobile quality is set to 96kbps, the desktop and high quality mobile one comes with 160kbps and Premium subscribers can make use of 320kbps streams on any platform.
Albeit you could be inclined to believe that 256kbps isn't as good as 320kbps, the truth is that there's a very small difference as far as song quality, and there's also an ongoing debate as to whether human ears can effectively discern differences in quality at higher bitrates.