Automatic call screening is one of the headliners of the December Pixel feature drop, and it has started to roll out to the first Pixel 4 units on the latest security patch level. Once it has arrived, it will automatically be deployed to deal with spam calls, and it can be activated for unknown, private, or possibly spoofed numbers, as well. The feature now also widely offers to save audio from any screened call in addition to the familiar transcript, just as we suspected from teardowns.
When the feature becomes available to you, you'll find the option to tweak the automatic Call Screen in the Phone app's settings under 'Spam and Call Screen.' You'll be able to set up different actions depending on what kind of number is calling. By default, detected spam numbers will be declined automatically, but others like first-time callers or possibly faked, private, or hidden numbers will ring your phone. You can adjust that behavior individually for each category and ask Google Assistant to screen calls before alerting you.
Additionally, it'll be possible to save Call Screen audio from calls your Assistant answered, which you'll have to explicitly enable in the feature's settings. It's unclear whether that option will be available in every location since recording your phone calls might be illegal depending on where you live.
The new functionality should arrive on your Pixel 4 once the Android 10 December security patch hits it, but keep in mind that it's limited to the US for now. Other goodies from the Pixel feature drop are already rolling out as app updates to the respectively supported Pixel devices.