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+---
+c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_HTTP_VERSION
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_ALTSVC (3)
+  - CURLOPT_HTTP09_ALLOWED (3)
+  - CURLOPT_HTTP200ALIASES (3)
+  - CURLOPT_SSLVERSION (3)
+---
+
+# NAME
+
+CURLOPT_HTTP_VERSION - HTTP protocol version to use
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);
+~~~
+
+# DESCRIPTION
+
+Pass *version* a long, set to one of the values described below. They ask
+libcurl to use the specific HTTP versions.
+
+Note that the HTTP version is just a request. libcurl still prioritizes to
+reuse existing connections so it might then reuse a connection using an HTTP
+version you have not asked for.
+
+## CURL_HTTP_VERSION_NONE
+
+We do not care about what version the library uses. libcurl uses whatever it
+thinks fit.
+
+## CURL_HTTP_VERSION_1_0
+
+Enforce HTTP 1.0 requests.
+
+## CURL_HTTP_VERSION_1_1
+
+Enforce HTTP 1.1 requests.
+
+## CURL_HTTP_VERSION_2_0
+
+Attempt HTTP 2 requests. libcurl falls back to HTTP 1.1 if HTTP 2 cannot be
+negotiated with the server. (Added in 7.33.0)
+
+When libcurl uses HTTP/2 over HTTPS, it does not itself insist on TLS 1.2 or
+higher even though that is required by the specification. A user can add this
+version requirement with CURLOPT_SSLVERSION(3).
+
+The alias *CURL_HTTP_VERSION_2* was added in 7.43.0 to better reflect the
+actual protocol name.
+
+## CURL_HTTP_VERSION_2TLS
+
+Attempt HTTP 2 over TLS (HTTPS) only. libcurl falls back to HTTP 1.1 if HTTP 2
+cannot be negotiated with the HTTPS server. For clear text HTTP servers,
+libcurl uses 1.1. (Added in 7.47.0)
+
+## CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE
+
+Issue non-TLS HTTP requests using HTTP/2 without HTTP/1.1 Upgrade. It requires
+prior knowledge that the server supports HTTP/2 straight away. HTTPS requests
+still do HTTP/2 the standard way with negotiated protocol version in the TLS
+handshake. (Added in 7.49.0)
+
+## CURL_HTTP_VERSION_3
+
+(Added in 7.66.0) This option makes libcurl attempt to use HTTP/3 to the host
+given in the URL, with fallback to earlier HTTP versions if needed.
+
+## CURL_HTTP_VERSION_3ONLY
+
+(Added in 7.88.0) Setting this makes libcurl attempt to use HTTP/3 directly to
+server given in the URL and does not downgrade to earlier HTTP version if the
+server does not support HTTP/3.
+
+# DEFAULT
+
+Since curl 7.62.0: CURL_HTTP_VERSION_2TLS
+
+Before that: CURL_HTTP_VERSION_1_1
+
+# PROTOCOLS
+
+HTTP
+
+# EXAMPLE
+
+~~~c
+int main(void)
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    CURLcode ret;
+    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
+    curl_easy_setopt(curl, CURLOPT_HTTP_VERSION,
+                     (long)CURL_HTTP_VERSION_2TLS);
+    ret = curl_easy_perform(curl);
+    if(ret == CURLE_HTTP_RETURNED_ERROR) {
+      /* an HTTP response error problem */
+    }
+  }
+}
+~~~
+
+# AVAILABILITY
+
+Along with HTTP
+
+# RETURN VALUE
+
+Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.