* Jordan Justen <jljusten@debian.org>, 2025-04-10 11:06:
Debian contains a b3sum package, which is a utility to calculate and verify blake3 hashes. The b3sum package does not provide development library support.
FWIW, there'a also rust-blake3. As the name hints, it builds only a rust dev package, but AFAICS the source package contains also the C code you had it mind.
-- Jakub Wilk