What is HTTP 426 Status Code (Upgrade Required)?

Reliqus Marketing

03 June 2024

HTTP Status Codes

Have you ever encountered an HTTP 426 Status Code while browsing the web and wondered what it means? Don’t worry, you’re not alone. The 426 Upgrade Required response status code is not as commonly seen as other HTTP codes, but it is important to understand its meaning and implications.

At Reliqus Consulting, we believe in empowering our clients and readers with comprehensive knowledge about such technical details, which can often be pivotal in optimizing your digital platforms. 

In this blog post, we will delve into what the 426 HTTP Status Code means, why it occurs, and how it should be handled.

What Does HTTP 426 Status Code Mean?

A 426 Status Code is an HTTP response status code that means “Upgrade Required.” It indicates that the server refuses to perform the request using the current protocol, but it is willing to do so after the client upgrades to a different protocol.

It is MUST for the server to send an Upgrade header field in the 426 response so it can indicate the required protocol(s).


HTTP/1.1 426 Upgrade Required

Upgrade: HTTP/3.0

Connection: Upgrade

Content-Length: 53

Content-Type: text/plain

This service requires use of the HTTP/3.0 protocol.

Upgrade RFC7230 Section 6.7

Source: RFC7231 Section 6.5.15

426 HTTP Status Code Usage

The HTTP 426 Status Code is implemented on websites primarily through an HTTP connection.  For instance, initiating a Websocket connection or transitioning from HTTP/1 to HTTP/2 (non-TLS) typically involves utilizing the Upgrade header in the request. Normally, a server responds to such requests with a 101 Switching Protocols status. 

However, a server might issue a 426 Status Code error to explicitly mandate this protocol switch.

426 HTTP Response Status Code References

Rails HTTP Status Symbol :upgrade_required

Symfony HTTP Status Constant Response::HTTP_UPGRADE_REQUIRED

.NET HttpStatusCode.UpgradeRequired

Rust http::StatusCode::UPGRADE_REQUIRED

Go http.StatusUpgradeRequired

Python 3.5+ http.HTTPStatus.UPGRADE_REQUIRED

Apache HttpComponents Core org.apache.hc.core5.http.HttpStatus.SC_UPGRADE_REQUIRED

Angular @angular/common/http/HttpStatusCode.UpgradeRequired

426 Upgrade Required Status Code Example

An example of an HTTP 426 status code request and response is shown below:


GET /index.html HTTP/1.1

Host: www.example.com

Connection: keep-alive

Upgrade: TLS/1.0


HTTP/1.1 426 Upgrade Required

Date: Wed, 14 Jul 2021 17:00:00 GMT

Server: Apache

Upgrade: TLS/1.0, HTTP/1.1

Connection: Upgrade

Content-Length: 73

Content-Type: text/plain; charset=utf-8

This server requires the use of a secure connection. Please upgrade to TLS/1.0.

What Causes a 426 HTTP Status Code?

The triggering of a 426 HTTP Response Status Code occurs when there’s a mismatch or requirement for an upgrade in the communication protocol between the client and the server. 

Here are some of the primary reasons why this code might be encountered:

  • Incompatibility Issues: The client is using an older or incompatible version of the protocol that the server no longer supports or refuses to handle for the requested action.
  • Unsupported Protocol Version: The server does not support the protocol version the client is attempting to use, necessitating an upgrade to a version the server accepts.
  • Restrictive Server Configuration: Some servers are configured to only allow connections via specific protocol versions for security, performance, or other reasons, leading to the 426 status code error if the client’s request doesn’t match these configurations.
  • Server Limitations or Maintenance: Occasionally, servers undergoing maintenance or facing technical limitations may temporarily be unable to support protocol upgrades, resulting in a HTTP 426 status code being returned to the client.

In situations where a 426 error is encountered, it is crucial for the client side to investigate the specific cause and explore the necessary steps to facilitate a successful connection using an upgraded or compatible protocol version.

Which HTTP Method is used with HTTP 426 Status Code?

For the 426 HTTP Status Code, the HEAD method is the only method used. A server uses the 426 HTTP Response Status Code to inform a client that it has a newer version or uses a different protocol to communicate with it. A HEAD method requests the same response as a GET request, but the response body is not included.

426 Upgrade Required Status Code Error Implications for SEO

Understanding the implications of a HTTP 426 status code is crucial, and Reliqus Consulting provides expert insights and solutions to maintain your website’s SEO health in such scenarios.

  • Impact on Crawling and Indexing: When a search engine crawler encounters a 426 HTTP status code, it’s unable to access and index the page’s content. This can lead to the page not appearing in search results, directly affecting the site’s visibility and organic traffic.
  • Negative Impact on Search Engine Rankings: Websites with frequent 426 errors code may be indexed improperly, leading to decreased search engine rankings. Search engines prioritize websites that provide a seamless user experience, including easy content accessibility.
  • Perception of Website Reliability: A high occurrence of 426 HTTP errors might signal to search engines that a website is unstable or poorly configured. This perception could diminish the site’s trustworthiness and reliability in the eyes of both users and search algorithms, further impacting SEO performance.

How to Troubleshoot a 426 Error Upgrade Required Status Code?

Troubleshooting a HTTP 426 status code involves identifying and rectifying the mismatch between the client’s request protocol and the server’s supported protocols.  

Here are effective steps to tackle this error:

  • Check for server configuration issues: It’s crucial to verify the server’s configuration supports the protocol version requested by the client. Specifically, ensure the server is configured to support HTTP/1.1, as this is foundational for handling protocol upgrades. Adjusting the server to accommodate the requested protocol might be necessary.
  • Check for client-side issues: Errors can also stem from the client sending incorrect or unsupported upgrade headers. Review the client-side code to confirm it’s dispatching the correct headers and is compatible with the protocol version it’s attempting to utilize.
  • Check for network issues: Sometimes, the problem lies within network connectivity. Verify that both the client and server are on the same network and inspect firewall or proxy settings that could be impeding the connection. Adjustments to these settings may be required to allow for proper communication.
  • Update software versions: Outdated server or client software can be a significant barrier to protocol compatibility. Ensuring both the client and server are running the latest software versions can mitigate issues related to outdated protocols, facilitating a smoother upgrade process.

How Reliqus Consulting Can Help?

Reliqus Consulting understands that navigating through the complexities of HTTP status codes can be challenging. The HTTP 426 Status Code, although not frequently encountered, is a crucial part of maintaining forward compatibility and security in web communications. 

To learn more about different HTTP status codes and how they impact your digital projects, feel free to explore our detailed guide on HTTP Status Code.

Whether you’re looking to troubleshoot an HTTP 426 error code or need a comprehensive evaluation of your current web protocols, our team is here to assist. We specializes in providing top-tier web development and management services that help you stay ahead in the digital race. 

Understanding and implementing the right HTTP protocols forms a core part of our strategy to enhance your web presence. Contact us today to see how we can assist in optimizing your digital operations for the modern web landscape.


Frequently asked questions about the 426 HTTP Status Code cover its detection, related headers, and browser compatibility. Here are some key queries answered:

How to Check HTTP 426 Status Code?

Use the web browser’s network tab and developer tools to inspect the response codes for resources requested by the client.

What are the Related HTTP Response Headers with 426 HTTP Status Code?

The Upgrade HTTP Header is the primary response header associated with the 426 HTTP Status Code. It indicates the required protocol to which the client should switch.

What are the Browsers Compatibility of HTTP 426 Status Code?

426 status code is recognized and handled by all major browsers, including Chrome, Edge, Firefox, Internet Explorer, Opera, Safari, and Webview Android.

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