You can use Google Assistant that lives in your phone via the QC35II headphones, which seemed like an interesting feature at first, but the experience falls flat.
To issue voice commands, you have to press and hold the button on the left ear cup, and Google Assistant will give you its reply.
It does work for simpler questions, like getting the weather and other questions you can search on the web, and it can tell you your next calendar event, too. But there's a significant delay between your voice command and the answer from Google Assistant. I couldn't imagine a scenario at home when I'd use Google Assistant on the QC35II headphones, and speaking to voice assistants out in public isn't something I'm ready to do. Plus, if you have reach up to press and hold the button for Google Assistant, you might as well reach for your phone.
I also tried some more complex things like sending a message and getting direction using Google Assistant with the QC35II, but it never worked properly.
You can also get notifications from your phone to the headphones, but this interrupted music or quiet moments so often that it became unbearable. I turned off all the notifications with angry satisfaction.
Apple claims it works with Siri on its website, too, but I found no compatibility with Siri in the Bose app settings on an iPhone X.