Looks like they do little more than just check for a Google cookie [1].
[1]. https://www.blackhat.com/docs/asia-16/materials/asia-16-Siva...
edit: still, it's far better than the previous state of captchas. I'm glad they did this. But it's like for anything to be considered "advanced" or "good" in tech lately, it has to have been powered by "machine learning".
(That said, whenever I used that checkbox widget they had before this announcement, there was a noticeable framerate drop in the browser while the thing was doing its magic. So I suspect, they are at least doing some browser fingerprinting/benchmarking to see if the widget runs inside selenium or a stock browser.
I also remember rumors that they analyze keyboard/mouse input on the page and check if it looks "human", but I'm not sure if that's true.)
If your browser is standard (AKA no anti-fingerprinting plugins) and your advertising cookies are not blocked (privacy or adblocker plugins) you'll probably pass with no issues.
If either of those is not true, you have to solve a bunch of image captchas.
Mouse/keyboard input analysis was just marketing talk; at least when they first released the nocaptcha it wasn't even captured.