Question

If I develop with version 1.2.6 of the App Engine SDK, once I publish to production will my app still be using version 1.2.6 of all of the libraries on the production app engine? Or will it automatically use the latest version of the core app engine libraries?

Answer 1

It looks like it will continue to use the old libraries until you manually upgrade the libraries contained in your application. From the Google App Engine Java documentation:

This API is represented by the
appengine-api-*.jar included with the
SDK (where * represents the version of
the API and the SDK). You select the
version of the API your application
uses by including this JAR in the
application’s WEB-INF/lib/
directory. If a new version of the
Java runtime environment is released
that introduces changes that are not
compatible with existing apps, that
environment will have a new version
number. Your application will
continue to use the previous version
until you replace the JAR with the new
version (from a newer SDK) and
re-upload the app.