@Clustered can be applied as follows:

• Entity EJB - Give a "feature unsupported" error, refuse to deploy
• Stateful Session EJB - Allow
• Stateless Session EJB - Allow (has no effect though)
• Singleton EJB - Give a "feature unsupported" error, refuse to deploy
• MDB - Give a "feature unsupported" error, refuse to deploy

Note that "feature unsupported" should be worded such that the feature may become available in future releases.