Update on 17/11/19:
Google have informed me that as of the end of November 2019:
... App Engine Standard will use Google Cloud Build during deployments to build your code into a container before running it on our platform.
Cloud Build requires all projects to be linked to a billing instrument (for example, a credit card), so please ensure your projects containing App Engine applications are linked to a billing account with a valid billing instrument. Applications without billing instruments will be unable to deploy after November 30, 2019. If your projects are already linked to billing accounts with a valid billing instrument, you can stop reading now.
As I don't particularly want to give Google my credit card number and I can now embed Sketchfab models directly into my blog pages then I'll probably stop updating this App Engine page. However I will leave the content here for as long as possible.
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