Force Touch Stems
As noted earlier, the stem of each AirPod now provides the ability to switch noise cancellation and transparency modes by pressing firmly and holding with a “force touch” gesture. This can also be customized in your AirPods Pro settings on the iPhone (found under Settings->Bluetooth) to either switch one of the modes on or off, cycle between all three settings, or to active Siri. The settings are independent for each AirPod too, so you could use the left stem to trigger Siri and the right to switch noise cancellation and transparency modes, or even set one AirPod to toggle noise cancellation on and off and the other to toggle transparency on and off.
The stem of each AirPod also now provides standard playback and call controls via a short force touch press, similar to other Apple headphones. A single short press pauses or resumes your music. If your iPhone is ringing, it will also answer a call, or end a call in progress. A double-press will skip to the next track, and a triple-press will skip back to the beginning of the current track or the previous track.