---
name: "CURLOPT_HTTP_VERSION"
section: "3"
platform: "macos"
package: "curl"
version: "166.0.0.0.1"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_HTTP_VERSION"
---

# CURLOPT\_HTTP\_VERSION(3)

HTTP protocol version to use

## NAME

CURLOPT\_HTTP\_VERSION - HTTP protocol version to use

## SYNOPSIS

```
#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)](/CURLOPT_SSLVERSION/3.md)*.

  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

```
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.

## SEE ALSO

[**CURLOPT\_ALTSVC**(3)](/CURLOPT_ALTSVC/3.md), [**CURLOPT\_HTTP09\_ALLOWED**(3)](/CURLOPT_HTTP09_ALLOWED/3.md), [**CURLOPT\_HTTP200ALIASES**(3)](/CURLOPT_HTTP200ALIASES/3.md), [**CURLOPT\_SSLVERSION**(3)](/CURLOPT_SSLVERSION/3.md)