Piwigo 12 is just a few days (or weeks) ahead and many extensions (plugins and themes) won't be automatically compatible. They won't need a lot of changes, but your extensions will need some updates.

Matthieu and I have prepared a page with the a checklist on Technical changes in Piwigo 12. Here is the short summary:

* "Has Settings" is now mandatory
* Prefilters slightly changed with the new version of Smarty template engine
* Smarty template variables need to be checked before being used
* for remote applications, you must (strongly encouraged to) declare the end of upload
* MySQL and reserved keywords ("groups" and "rank") must be escaped


A) if you have changes on your code, publish a new revision of your extension, compatible 12

B) if you have no change and don't feel the need to have a new revision, mark your latest revision as compatible with version 12

We're here if you need any help :-)