[yegle]

Disclaimer: I work for Google on App Engine.

We usually extend the deprecation timeline if a product is important or is hard to migrate.

Master/Slave datastore deprecation takes 3 years since the announcement of deprecation.

Python2.5, 4 years since deprecation announcement to fully deprecated.

Java 6 was officially deprecated in July 2017 but if you still have an app deployed in Java 6, chances are they can still serve traffic just fine. Same applies to Java 7 (this is partially due to JVM backward compatibility but there are non-trivial engineer works involved)

I hope this gives you some confidence in Google's cloud offering.

For all deprecated features of App Engine, you can see https://cloud.google.com/appengine/docs/deprecations/ (note alpha/beta features are deprecated in less than 1 year which is WAI)