Facebook is doing some ugly hacks over libsodium. https://github.com/facebook/folly/blob/master/folly/experimental/crypto/LtHash.cpp … I’m all for adding a XOF to libsodium and BLAKE2X would be a natural choice. The only thing I really don’t like about it is its pointless incompatibility with BLAKE2 for short output sizes.
The initial version of libhydrogen used to provide a unified API, that transparently picked either BLAKE2 or BLAKE2X according to the output size. But that’s clunky and shouldn’t be necessary. I don’t want to do that again in libsodium.