How many letters does the top answer for “wrote i am a cat” have?

The most common answer is soseki (6 letters).

Crossword clue: wrote i am a cat

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

soseki 6 letters wd-fact-v3

author of i am a cat 50% similar → soseki

wrote cat and mouse 50% similar → grass

wrote the black cat 50% similar → poe

wrote the cats of ulthar 50% similar → lovecraft