In reverse proxy mode 1.3.26, is HTTP 1.1 always used?

[Gael Marziou]

Hello,
I'm using Apache 1.3.26 mod_proxy in reverse proxy mode, I'd like to 
know whether the protocol used on web server side is always HTTP 1.1 or 
if it could be HHTP 1.0 depending on some conditions.

Client -> Reverse Proxy -> Web Server
Thanks,
Gael