# 426 Upgrade Required

> The server refuses to perform the request using the current protocol.

Source: https://apiguide.dev/status-codes/426
Class: client-error
Defined in: RFC 9110, Section 15.5.22 <https://www.rfc-editor.org/rfc/rfc9110.html#section-15.5.22>
Updated: 2026-07-09

## What does HTTP status code 426 mean?

The 426 Upgrade Required status code indicates that the server refuses to execute the request unless the client upgrades to a newer protocol (like HTTP/2 or TLS 1.3).

## When to use it in APIs

Used to force old API clients or mobile apps to update their connection libraries to support secure protocols.

## How it compares to other codes

* **101 Switching Protocols**: An agreement by the server to switch. 426 is a *requirement* that the client upgrade before proceed.