You can apply to receive your S.M. degree en route to your PhD after you have completed eight of your core courses (this requirement may depend on area). You will receive your S.M. diploma, and participate in the Commencement if you choose to. However since you will be considered a non-terminal degree recipient, you will not be able to join the ceremony in Sander's Theater. Details: https://gsas.harvard.edu/academics/commencement
