The split between the `Extremists` and `Moderates` occurred at the Surat Congress Session in the year 1907. This marked a significant moment in the Indian National Congress as it led to a division in their approach to the freedom struggle. The `Moderates` were a group of Congress leaders who believed in a more gradual and peaceful approach to achieving independence from British rule. On the other hand, the `Extremists` advocated for a more radical and militant approach. The split at Surat Congress Session was a result of differences in ideologies and tactics between these two groups. It is important to note that while the answer provided is generally correct, it`s worth mentioning that the split started to surface in the years leading up to the Surat Congress Session.