UPDATE (2014-09-30): In response to feedback from developers, we're delaying the breaking change to the "Add team member" API until Monday, October 6, 2014. The change will go into effect for all requests on that date.
Starting October 6, if you use the "Add team member" API to add a user to a team and that user isn't already on another team in your organization, the request will fail. To avoid this, be sure to use the "Add team membership" API.
The Organization and Team Membership APIs are now official
As promised in our blog post earlier this month, the Organization Membership and Team Membership APIs are now an official part of the GitHub API! The preview media type is no longer required to access them.
If you have any questions or feedback, please get in touch with us!