How many letters does the top answer for “which car is the first mass-produced hybrid vehicle” have?

The most common answer is prius (5 letters).

Crossword clue: which car is the first mass-produced hybrid vehicle

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

prius 5 letters otdb

toyota 6 letters otdb

an industrial city of Japan in southern Honshu