Kuhpāyi is a Central Dialect spoken in Kupā township and its piedmont villages, east of Isfahan. While it shares many traits with other Northwestern Iranian dialects of the central Iranian Plateau, Kuhpāyi has many characteristics of its own. In historical phonology, it shows some remarkable Southwestern Iranian features, as in hass 'eight'. Peculiar in its phonological structure is the central vowel /ə/, which harmonizes in the verbal forms. The dialect’s transitional characteristic is exemplified in the unstable position of the durative marker before the stem. The past tenses of transitive verbs have an ergative inflexion, with the agential affixes shifting from the verb to the preceding word, including the subject itself — a trait found in no other known Central Dialect. This article studies the diachronics and grammar of Kuhpāyi, followed by texts and by a glossary based on the documentation gathered by the author on this vanishing dialect.