We knew that Apple wasn't about to spring a surprise and offer CD-quality, lossless streams to match Tidal and Qobuz, so the smart money has always been on Apple Music offering 256kbps AAC streams.
Why? AAC is Apple's format of choice and 256kbps is what you'll get when you buy an iTunes download or use the iTunes Match service to upload your library to Apple iCloud.
There's no hint of confirmation from Apple on this, be it online or in the new Music app, which launched as part of iOS 8.4. There is however some information in the latest version of iTunes, which was released a few hours after the Apple Music launch.
Head to the My Music tab, right-click on the track and then select Get Info to see the file information.
The File tab on the far right shows that Taylor Swift's Shake It Off is a 256kbps AAC file. As noted, this is the file stored by Apple Music in iCloud (see above).
By contrast, a WAV file stored locally on the Mac in question is shown as such, complete with higher bitrate and the different location (see below).
MORE: Apple Music review
More after the break
This still doesn't categorically confirm the streaming rate, just the size and format of the audio files stored in Apple Music - not least as Apple's Eddy Cue has confirmed that the streaming bitrate will vary depending on whether you're streaming over a cellular or Wi-Fi connection.
@HiFiGuy528 bit rate depends on whether you are on WiFi or cellular
— Eddy Cue (@cue) July 1, 2015
Other services do also advertise their streaming rates as at 'up to...' a given bitrate, so there's nothing to suggest other services aren't doing something similar without the user's knowledge.
There's no denying you're in the dark on audio quality when it comes to Apple Music, though. Tidal and Spotify, for example, allow you to set your preferred streaming rates.
Tidal offers a choice of Normal at AAC+ 96kbps, High at AAC 320 and HiFi at FLAC 1411 (on desktop), for example. There's no such option like this in Apple Music.
While all this is of interest for how good your music sounds, it's also useful for knowing how much data you're using when you're streaming tracks over your mobile phone network.
We'll get to the bottom of all this, and more importantly deal with the crucial issue of how good Apple Music sounds and how it compares to its rivals, in our full review, coming very soon.