0.16.0 (October 6th, 2020)

Changed

• Preserve HTTP header casing. (Pull #1338, encode/httpcore#216, python-hyper/h11#104)
• Drop response.next() and response.anext() methods in favour of response.next_request attribute. (Pull #1339)
• Closed clients now raise a runtime error if attempting to send a request. (Pull #1346)

Added

• Add Python 3.9 to officially supported versions.
• Type annotate __enter__/__exit__/__aenter__/__aexit__ in a way that supports subclasses of Client and AsyncClient. (Pull #1336)