The Android library, which is an AAR file, is a tiny 220 KB.

The iOS library, which is a framework, is about 240 KB (after compression and for a specific device).

Given how frameworks operate for iOS, the compressed framework itself is 4.7 MB, and then automatically reduces down radically depending on the specific mobile device architecture (i386, x32_64, armv7, armv7s and arm64) and bitcode support (app thinning, which allows to only retain the required architecture).  

This is typically much smaller than traditional push notification providers.