So for Android there are two large "parts" to the latest OS. First you have the latest major version (ex 8.1 or Android Oreo SR1) and then you have the security patch level (which is usually a date).

Additionally there is also the Google Play layer of the Android OS. Google Play is optional but it provides a host of Android security features like malware scanning. https://developers.google.com/android/reference/com/google/android/gms/safetynet/package-summary

As far as determining the newest version of Android goes, I can only think of lots of options which are all some variation of "Call a server and ask".