Stadia controllers support Bluetooth for the initial setup, and with that Bluetooth Low Energy technology baked in some suspected that it might allow for a connection to a Bluetooth headset or earbuds for use with the audio. Turns out that won't be possible, at least not at launch, according to Andrey Doronichev who is Stadia's Director of Product.
Doronichev, who hosted Stadia's first official AMA over on Reddit this morning, was asked if the controller would support connection of Bluetooth headsets if players wanted to stream the audio to them to afford a little more privacy. The answer given may be one that consumers were hoping would be different, as you'll need to plug a pair of wired headphones into the 3.5mm audio jack on the bottom of the controller.
This leaves room for the possibility of Bluetooth headsets being supported at some point in the future, though, so not all hope is lost if you were wanting this particular feature to be present on the platform. The issue here for some will be that there's currently no timeframe for when Bluetooth audio will be supported by the controller. If it ends up being added though Google is likely to put that on its features roadmap that's coming in the future.
If you're disappointed by the lack of Bluetooth audio support for Stadia's official controller, Doronichev does provide some light at the end of the tunnel that can be taken advantage of at the beginning of Stadia's launch period. There is one way to use Bluetooth headphones with Stadia in November, and that's if you're accessing Stadia from a PC or one of the supported Pixel 3 devices.
According to Doronichev you can still connect your Bluetooth headphones to your PC or your smartphone and the audio for games will go through the headset that way. So while the controller doesn't directly support it, the device with which your using to access Stadia will.
Though it isn't mentioned, the same is also likely to be true for TV's that have Bluetooth support. For anyone using the Chromecast Ultra to access Stadia, if the TV that the Chromecast Ultra is plugged into allows for a connection of Bluetooth headphones, then there's no reason to suspect that audio for the games you're playing won't come through the headphones instead of the TV's speakers.
Considering these things it might seem like there is little reason to add Bluetooth audio support to the controller itself. However, if the controller did have this option then it would pick up some of the slack from the battery drain that would be placed on Pixel 3 phones if users wanted to listen to game audio wirelessly, and this would be enough of a reason to add it as it could help extend gameplay time.
Still, even if Bluetooth will work in a roundabout way there's still the question of whether or not connected Bluetooth headsets will support the platform's voice chat which is due to be one of the service's launch features. If the platform-level voice chat requires a headset connected to the controller, then players will be forced to use a wired headset in order to use it, which might cause issues for those that don't own wired headsets.