Three different conceptual models have been proposed for the Cenozoic subduction style in South Asia, including Greater India, Intra‐oceanic Arc, and Continental Terrane (or Greater Indian basin). Since these models imply distinctive origins for the Tethyan–Greater Himalayan (TGH) sequences, for example, as a relic of the subducted Greater India or Gondwana–affiliated continental terrane, quantitively reproducing the relic TGH crustal mass with numerical models could help further constrain the debated Cenozoic subduction history between India and Eurasia. Based on the modeling results, we show that the subducted plate since the Paleocene should consist of a significant oceanic portion that is, ∼1,000 km long for the Intra‐oceanic Arc model and up to 2,000 km long for the Terrane model. Our results do not support the existence of a continuous >3,000 km long continental Greater India before the early Eocene collision in South Asia. Plain Language Summary Approximately 55 million years ago, the Indian Subcontinent was in the Southern Hemisphere, >3,000 km away from Tibet. However, it remains unknown what tectonic units were between them. Previous studies suggest that this region was composed of either pure land or with parts being oceans. By now, this region has mostly foundered into the deep Earth, with its surface relics forming the Himalayan Mountains. Because land and ocean contribute differently to the relic materials, the mass of the Himalayan Mountain can provide essential information about this lost tectonic region. This study uses numerical models to replicate the relic Himalayan mass while evaluating the earlier proposed models. We found that to match the Himalayan mass, the region between Tibet and India ∼55 million years ago could not be purely continental and should include >1,000 km long oceanic plate. Key Points Different models of Cenozoic subduction history in South Asia imply distinctive origins for the Tethyan–Greater Himalayan sequences Quantitively reproducing the Tethyan–Greater Himalayan mass helps constrain the Cenozoic subduction history in South Asia Both the Intra‐oceanic Arc and Terrane models, but not the Greater India model, could have been operating during the Cenozoic subduction