Is ITIL 4 Training mandatory for candidates or can they self- study?

AXELOS has not mandated training for ITIL 4 Foundation, so you are able to self-study. However, candidates are encouraged to attend an accredited training course to fully understand the new material. 

For all modules in the ITIL 4 Managing Professional and ITIL 4 Strategic Leader designations (including the ITIL 4 Managing Professional Transition module) training is mandatory to enable candidates to fully understand the new material.