How does 'squeeze your pixel2' to launch the assistant actually work?

HTC did indeed introduce this feature, but it was just a few months ago on the HTC U11.

The feature works identically on the new Pixel 2 and 2 XL in terms of squeezing. You can adjust how much pressure it takes to launch, and it works in a case as well. All it does is open up Google Assistant, or silence an incoming call if you squeeze while it's ringing.

Unlike the U11, it isn't configurable. The U11 was only slightly configurable out of the box, and a later software update added much more functionality and options. I could easily see Google doing the same with Android 8.1.

After your initial period of testing the Pixel 2 and 2 XL how often did you incidentally trigger the assistant by squeezing the phone while pulling it out of your pockets. Does this feature also work while the screen is off?
 
Exactly, they should have just left it open to use as HTC did, I hate the "bixby" button. My wife has it the s8 and it's just a waste of a button.