GeneXus Access Manager (GAM) is under constant development and compatibility aspects may need to be taken into account when updating a solution or application, that uses GAM, to a newer version of GeneXus.
Since new versions of GAM are released together with GeneXus versions (and their upgrades), compatibility aspects are documented thoroughly in the release notes of each version.
That is to say, that an overview can be found in the compatibility section of the corresponding release notes in this wiki (eg GeneXus 16 Upgrade 11) and details at the Release notes site (eg.: filter Type="Compatibility" and search for GAM)
Every time the Database is also reorganized, those changes maintain backward compatibility (*). That is to say, if in version X of GeneXus, GAM's schema changes from M to N, programs generated with versions X-1 or prior still keep working with version N. So, that database still can be accessed by programs generated for GeneXus versions X-1 or prior and also by programs generated for GeneXus version X.
Sample: GAM's schema changed from version 4.0.3 to 4.0.4 in GeneXus 15 Upgrade 11. Applications generated with GeneXus 15 Upgrade 10 or prior can still access the database. Programs generated by GeneXus 15 Upgrade 11 or higher require schema 4.0.4.
This is a very important aspect since it allows you to update applications incrementally (you do not need to update all at once).
(*) Only exception to the rule were certain cases related to 3.0.5 > 3.0.6