The Talmud, at Shabbat 104a, preserves a specific rabbinic debate about the authority behind Final Kaph and the four other sofit letters as a group: it records the statement mem, nun, tzadi, pe, kaph, tzofim amaram, the prophets said them, meaning tradition credited early prophetic figures with fixing which five letters take a distinct shape at the end of a word, against a rival view that the forms were only formally confirmed later, by the men of the Great Assembly in the early Second Temple period. The Talmud does not fully resolve which account is correct, treating the final forms as halacha le-Moshe mi-Sinai in some readings, a law transmitted to Moses at Sinai without a documented origin story, rather than a script decision made at any single datable moment.
Final Kaph's own shape, a single stroke descending well below the writing line, is visually one of the more distinctive of the five, though beginning readers and, occasionally, careless scribes have been known to confuse it with final Nun, a plainer descending stroke, or with the ordinary letter Vav, making correct proportion here as important as the debate over the form's origin is unresolved. In the extended gematria system known as mispar gadol, discussed elsewhere in this atlas, Final Kaph carries the value 500, continuing the numeral sequence beyond the point where the ordinary twenty-two-letter count stops at 400 with Tav.