First off, Face Unlock can now account for changes to your look like a new hair style or beard. "When it's on, face unlock images are occasionally used to create improved face models," Google's update states. "This helps recognize you better over time." The update also points out that these models are stored on the Pixel 4's secure Titan chip and never online.
As expected, the update also brings T-Mobile eSIM support to Pixel 4 devices. That means you can activate your device immediately without waiting for the physical delivery of a SIM card, and also use the eSIM in conjunction with a physical SIM to receive calls and texts from two numbers. Finally, the Pixel 4 now supports dual-frequency GNSS so it can track two satellite signals at once, either from GPS or Galileo satellites. That in turn will deliver more accurate location tracking.
You can likely expect more such improvements via future Pixel 4 drops. With the new update stream, Google is clearly trying to differentiate its flagship devices from others in the Android ecosystem.