Airtable Extensions, available on Pro plans, are modular extensions that you can add to your bases to extend their functionality. They also look great in your Airtable Universe bases—try a map extension, or a chart extension!
If you have extensions installed in a base that you'd like to publish, you have a choice of whether or not you want those extensions to extensionear in Airtable Universe. At the bottom of the publish screen for your base, there is a Show extensions in published base toggle you can turn on.
When someone makes a copy of your Universe base that has extensions in it, those extensions will persist, i.e., their copy will include copies of the extensions that were in your base. If the person who copies your base is on a free or Plus plan after the initial Airtable trial expires, the extensions will be copied, but they will not be able to access or edit them (unless they upgrade to Pro in the future, at which point they will be able to edit or delete those extensions).
Note that when the base copy and included extensions are copied, API keys from extensions which use them are NOT copied over. The copying person will need to enter their own API key to enable those copied extensions.