In line with the commonly established notion of substantial modification for products regulated by Union harmonisation legislation, it is appropriate that whenever a change occurs which may affect the compliance of a high risk AI system with this Regulation (e.g. change of operating system or software architecture), or when the intended purpose of the system changes, that AI system should be considered a new AI system which should undergo a new conformity assessment. However, changes occuring to the algorithm and the performance of AI systems which continue to ‘learn’ after being placed on the market or put into service (i.e. automatically adapting how functions are carried out) should not constitute a substantial modification, provided that those changes have been pre-determined by the provider and assessed at the moment of the conformity assessment.