With 5G capabilities and a screen that could update 120 times per second, a large flagship-sized battery is called for. And while Google has disappointed often when it comes to providing enough battery capacity, indications are that a 5000mAh battery will be keeping the lights on the handset.
It isn’t clear how Google determines who gets invited to join the community but one guess is that the number of Pixel handsets that you’ve purchased is a factor. The invitation contains a link to a survey that asks a few questions including one about your purchases of Made by Google devices. The survey should take you just a few minutes to answer.