How many letters does the top answer for “author of project hail mary” have?

The most common answer is weir (4 letters).

Crossword clue: author of project hail mary

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

weir 4 letters wd-fact-v3

a low dam built across a stream to raise its level or divert its flow

composer of project hail mary 60% similar → gosling

director of project hail mary 60% similar → gosling

wrote project hail mary 60% similar → weir