Yes. The Internet-side client and the proxy server can use different protocols and versions that they can negotiate however they like, receive the HTTP request over those, and the proxy can use a separately-negotiated connection to your server to send that request over.
Essentially, the core of standard HTTP requests and responses (method, path, headers, response code) is fairly unchanged since HTTP/1.0, and what's changed is how those requests/responses are encoded and carried.
