The typing module was added to the standard library in Python 3.5, but many new features have been added to the module since then. This means users of older Python versions who are unable to upgrade will not be able to take advantage of new types added to the typing module, such as typing.Protocol or typing.TypedDict.

The typing_extensions module contains both backports of these changes as well as experimental types that will eventually be added to the typing module, such as Protocol.