https://wccftech.com/google-releases-android-go-to-oems-along-with-a-suite-of-low-end-google-apps/

In May 2017, Google introduced Android Go, a toned down version of Android for entry-level devices housing 512MB or 1GB RAM. At that time, we did not know when Google is going bring Android Go out in the open. Today, the company made it official alongside Android 8.1 Oreo.

As Google detailed at I/O 2017 conference too, Android Go is primarily made for making the Android experience smoother and better on low-powered devices. Therefore, Android Go is almost half the size of Nougat so that low-end devices can house it easily without losing much space.