status Registered
Verified 2026-09-18 · registry updated 2025-09-15

HTTP 426 Upgrade Required

The client must switch to another protocol to use the resource.

Use 426 when a protocol upgrade is required and identify it with an Upgrade header.

httpstatus codeprotocol

Response (http)

HTTP/1.1 426 Upgrade Required

Use 426 when a protocol upgrade is required and identify it with an Upgrade header.

Common mistakes

  • Sending 426 without an Upgrade header that names the required protocol.

Registry reference: RFC9110, Section 15.5.22

Sources

Permalink: https://merginit.com/reference/http/status-426