There is a small documentation misheap at https://pythonhosted.org/passlib/lib/passlib.hash.bcrypt.html#passlib.hash.bcrypt
For the ident parameter, it is first stated
Typically this option is not needed, as the default ("2a") is usually the correct choice
But the 2b value tells a different story
"2b" - latest revision of the official BCrypt algorithm, current default.
I'm guessing the actual default depends on the backend so I have no idea what to change