TypeScript tries to be sound too. It wouldn't really make sense to write a type checker if that wasn't your goal. As the person who wrote the "100% soundness is

TypeScript tries to be sound too. It wouldn't really make sense to write a type checker if that wasn't your goal. As the person who wrote the "100% soundness is a non-goal" line in the design goals document, that's there to serve the same role as "Flow sometimes has to make a tradeoff" in the Flow docs in terms of clarifying whether or not 100% soundness is a design goal. For both projects, the answer is "no". It's unfortunate that people have, over the years, decided that just being upfront about this fact means that TypeScript has a vastly different prioritization of soundness than Flow. We don't; both checkers use soundness as the default assumption when designing behavior.