Go 1.16 is now generally available.

Migrating from bundled services

Most of the functionality provided by the App Engine bundled services is now provided by the Cloud Client Libraries for Go. For more information, see the recommended alternatives listed below.

If migrating to an unbundled solution is not an option for your project, then you may be able to continue using App Engine bundled services in your Go 1.12+ apps as a fallback. This approach gives you flexibility to move to unbundled services later in the migration cycle.