We launched an application in the Apple AppStore and Google Play Store, and now we need to launch an update. But this update will change the server-side code (i.e. the API).
Does GeneXus handle multiple API versions? I mean, how to prevent that an app in the 1.0 version break when we launch version 1.1?
There are several considerations when publishing a new version of your application.
If you need both versions to be available at the same time, then the best option is to publish the new version's services to another URL. Say, for instance, you had version 1.0's services at https://example.com/myapp10, then create a new "virtual directory" https://example.com/myapp11 and make the new version point there.
A special consideration is needed if there are also changes in the database. If you only have new tables and/or attributes (and the new attributes are nullable), then you don't need to do anything else.
However, if you remove or change existing attributes, then the "old" services may not work with the new database schema. In that case, you'll also need to keep both versions of the database, and consider some replication mechanism to keep then in sync.
You may find this article interesting, about Pesobook application's deploy process (Spanish only).