Perlbal for the most part only speaks HTTP/1.0 both to clients and to
backend webservers.  It happily takes requests advertising HTTP/1.1
and downgrading them to HTTP/1.0 when speaking to backend serves.

It knows all about persistent connections (in both 1.0 and 1.1) and
will reply with HTTP/1.0 Connection: keep-alive the request was only
implicitly keep-alive with HTTP/1.1.  etc, etc.

Perlbal is now also starting to speak more of 1.1.  For instance,
Perlbal does support receiving transfer-encoding "chunked" requests
from clients (a feature of HTTP/1.1), will send a "100 Continue" in
response to "Expect: 100-continue", and will parse the chunked
requests, writing the request-of-unknown-length to disk (only if
buffered_uploads is enabled), and then will send an HTTP/1.0 request
to the backends, with the actual Content-Length (now known) filled in.

When more of 1.1 is supported, it will become an option, and later
become the default.  However, after several years of usage, there just
hasn't been that much of a reason.  The chunked requests (common from
mobile phones uploading large images) has been the most annoying
shortcoming but now that it's solved, it's questionable whether or not
more of HTTP/1.1 will be supported.