You don't submit to the API either a full password or a full hash (which, since Troy produced the hashes is identical). A hash is pretty much perfect for K-anon

You don't submit to the API either a full password or a full hash (which, since Troy produced the hashes is identical). A hash is pretty much perfect for K-anonymity because if you use a prefix like this then it's extremely likely your data will be spread across the buckets, so no 5-character prefix is close to uniquely identifying a password.