This undocumented change to the base provider class API contract (e.g. from a concrete to a static method) in MDL-82977 (5.0):

-    abstract public function get_action_list(): array;

+    abstract public static function get_action_list(): array;

Means that any sites with custom enabled AI providers will be broken upon upgrade to 5.0 - when editing a course settings page (or anywhere that uses an editor with AI prompt), for example, we get:

Edit course settings

Fatal error: Cannot make static method core_ai\provider::get_action_list() non static in class aiprovider_jokes\provider in /opt/moodle/master/src/ai/provider/jokes/classes/provider.php on line 38

This is a non-backwards compatible/breaking API change, and also means that AI providers that work on 5.0 can never work on 4.5, because we get the inverse error to that above:

Fatal error: Cannot make non static method core_ai\provider::get_action_list() static in class aiprovider_jokes\provider in /opt/moodle/45/src/ai/provider/jokes/classes/provider.php on line 38

This is perhaps less of a concern than those sites upgrading from 4.5 that will be broken until their AI providers are updated/fixed. We should ensure the API doesn't explode so dramatically, and ensure a smoother upgrade experience for our AI users