WordPress at a glance
filter is not described

http_request_version filter-hook . WP 2.7.0

Filters the version of the HTTP protocol used in a request.

Usage

add_filter( 'http_request_version', 'filter_function_name_1999' );
function filter_function_name_1999( $version ){
	// filter...

	return $version;
}
$version(string)
Version of HTTP used. Accepts '1.0' and '1.1'.
Default: '1.0'

Where the hook is called

WP_Http::request()
wp-includes/class-http.php 175
'httpversion' => apply_filters( 'http_request_version', '1.0' ),

Where the hook is used (in WP core)

Does not used.