https://www.theregister.co.uk/2018/07/25/google_app_engine_python_3/

Google App Engine will support two additional programming language runtimes in its standard environment in the next 30 days: Python 3.7 and PHP 7.2.

Oren Teich, product management director of Google Cloud Platform (GCP), heralded the long awaited arrival of the languages at Google Cloud Next '18 during a session on GCP serverless capabilities. A GCP blog post also said as much.