CB and K2 integration

Hi, is there any kind of intregration between CB and K2?
I'd like to let only the members of specific CB groups to add k2 articles

Yes, CB Articles and CB Blogs both integrate with K2 for displaying K2 articles on profile or storing blog posts in K2. Beyond that we've no further integration with K2.

I'd like to let only the members of specific CB groups to add k2 articles

CB does not have usergroups beyond Joomlas built in ACL. Groups provided by CB GroupJive are not access permissions and should not be attempted to be used as access permissions.

Thanks, by groups I actually meant subscription plans, wich are already aligned with joomla usergroups, so I guess I can use Joomla ACL with K2
I will explore K2 features then, thanks

If you're just assigning usergroups with CBSubs then yes those should work perfectly fine with K2.

My community members will be able to add their product and services ad K2 items, but their items should be visible to site visitors only until the author membership is valid

In my website, each subscription plan puts users also in a specific joomla usergroup.

Do you have any suggestion to implement such kind of solution?

I see Auto Actions has a feature to add new joomla/K2 items based on conditions, I was wondering if it was possible also to modify existing items when their author membership expires (i.e. unplublish the items, or set their visibility level only to superadmins)

I was wondering if it was possible also to modify existing items when their author membership expires (i.e. unplublish the items, or set their visibility level only to superadmins)

Yup, that's doable. See the below topic on how to execute an auto action based off subscription status.

www.joomlapolis.com/forum/277-cb-paid-subscriptions-support/243136-oncpayuserstatechange-is-firing-before-cb-fields-integration#321262

You can use that usage with a Query action to query the database and unpublish all K2 articles the user owns for example. If K2 has an API to do that you can use a Code action with Method set to PHP to run the necessary K2 PHP API.