_sources/in-depth/http.txt says that:

The default typedef for the HTTP client that is provided uses the
http_default_8bit_udp_resolve tag, and implements HTTP 1.0. The exact
typedef is in theboost::network::http namespace as the following: yada yada yada

But, boost/network/protocol/http/client.hpp defines BOOST_NETWORK_HTTP_CLIENT_DEFAULT_TAG to be tags::http_async_8bit_udp_resolve

Sorry if this isn't enough info, or if I'm reading things incorrectly. This is the first time I've posted a (potential) bug on github.