In Codebase you can create two types of Discussions in a project, a Private discussion, and a Public Discussion:
Public Discussions
A public discussion created in a project will be visible to all users in your Codebase account that have been assigned to the project, either through the project's assignments or their user role:
Any updates you make to the discussion are therefore set to public by default, but an individual update can be set to private, which will only allow users within the same company (as defined in your user management) to see the update:
Private Discussions
As with individual private updates, a private discussion is only visible to users within the same company, and therefore all updates made will be private, and cannot be changed.