Google reduced the size of app updates earlier this year with a new compression algorithm and now it is shrinking them again. Using the File-by-File patching technique, Google has reduced the size of Android app updates by 65% relative to the full app. Some patches will be 90% smaller.
As an example of how useful File-by-File patching is, Google says a patch to Google Maps that was previously 17.5 MB will now be 9.6 MB.
Since this technique uses more processing power and is notably more demanding on older phones, Google is only using it for auto-updates in the background.
This process will reduce daily data usage by an average of 6 petabytes.