Google is rolling out its April security patches/updates for its Pixel phones. Although functional notes this time around simply state a handful of fixes related to Bluetooth and keyboard lag, this update also delivers an anticipated "eyes open" requirement for the Pixel 4's face unlock, which first debuted with the recent Android 11 Developer Preview 2.
There's a short list of functional patches this month, and it's missing the face unlock change.
Build numbers are also the same across the board this time (QQ2A.200405.005, Apr 2020), without any specific images for specific carriers, like we've seen with some recent updates. Pixel and general Android security bulletins are also live. As usual, there are a ton of security fixes, including quite a few labeled "High" and "Critical," so it's in your best interests to update as soon as you can.
Google has updated its face unlock documentation today to state that an eyes-open requirement is now available. At the phone's original release, it was a point of contention that the security feature worked even when your eyes were closed, but the new setting (which appeared last month in the Android 11 previews) should make things a little more secure. The toggle that controls it should live in Settings -> Security -> Face unlock, Require eyes to be open. I should note, the feature was not enabled on my devices after the update, it had to be manually toggled on.
I'd also like to note that face unlock isn't running continuously when you're unlocking your Pixel 4, and that hasn't changed with this update. If it fails due to your eyes being closed, it won't succeed just because you then open them after it has already failed out. As before, it will need a new trigger for a scan. For example, swiping up to enter a pin/password/pattern, turning the display off/on again, or even just shaking the phone — it's funny, but it works.