[itcmcgrath]

This isn't true, but Cloud Spanner is awesome too!

[wilhuff]

It's probably better said that Cloud Firestore and Cloud Spanner share common infrastructure.

For example, Cloud Firestore uses TrueTime to provide similarly strong consistency guarantees to Cloud Spanner (see https://cloud.google.com/spanner/docs/true-time-external-con...)

I'm not aware of any whitepapers describing the listen feature that provides real-time updates.