The Backends API was originally introduced as way to provide non user-facing compute, with longer timeouts, different instance sizes, etc.
Beginning in 2014, we started recommending Modules, which were eventually
renamed to Services. During that time, we added
backend instances (
to all Services, thus removing much of the need for a separate Backends API.
On March 13, 2019, we will shut down the Backends API and all existing Backend versions. You will no longer be able to deploy new Backends or modify existing Backends, and these versions will stop serving traffic.