Firebase has announced a new optional upgrade called Firebase Authentication with Identity Platform, however, the new features already exist on the GCP Identity Platform.
As mentioned in the documentation here
Identity Platform serves as the backend for Firebase Authentication with Identity Platform and the features that are offered are identical.
I want to know:
In addition to @Alex's answer, upgrading to Identity Platform also let's use disable sign-ups and account deletion from the Firebase client SDK. It's useful when you want to restrict certain users to your application as you'll have to use the Admin SDK to create/delete users.
This along with blocking function and other features were part of Identity Platform already and you were able to upgrade your Firebase project before as well just like in the answer linked above. Firebase just made it easier for you to upgrade and use those features now directly from Firebase console.
Should we now choose to work with only one of Firebase Authentication with Identity Platform and GCP Identity Platform
If you plan to use only E-Mail Password authentication, Google Accounts and do not require blocking functions or so. You can keep using Firebase Authentication only as you won't be charged for it. However, if you upgrade to Identity Platform, you only have 3000 DAU for free.