Hi, because we want to have traits only as an option where people will be able to choose custom traits implementation, the Pharo kernel cannot depend on them. For that reason we had to flatten all classes that use traits in the kernel packages. That means that methods from system traits as TBehavior [1] were copied to the trait users and the traits were removed from the class definitions. For now these traits are still present in the image. If you use own traits in your projects, this step will have no impact on you. Only if your project extends the system traits, you will need to adopt it for Pharo 7. [1] complete list: TApplyingOnClassSide TBehavior TBehaviorCategorization TClass TClassDescription TComposingDescription TSortable TTranscript TTransformationCompatibility Cheers, -- Pavel