4xx Client Error

HTTP 426 Upgrade Required

The server refuses to perform the request using the current protocol but might do so after the client upgrades to a different protocol. The server sends an Upgrade header to indicate the required protocol.

Common Causes

  • Server requires HTTPS but request was sent over HTTP
  • Server requires a newer HTTP protocol version
  • WebSocket upgrade required for this endpoint

How to Fix

  1. 1Switch to the protocol specified in the Upgrade header
  2. 2Use HTTPS instead of HTTP
  3. 3Upgrade your client to support the required protocol

Example

HTTP 426 Upgrade Required
GET /api HTTP/1.1

→ 426 Upgrade Required
→ Upgrade: TLS/1.3
→ Connection: Upgrade

Related Client Error Codes

400

Bad Request

401

Unauthorized

402

Payment Required

403

Forbidden

404

Not Found

405

Method Not Allowed

406

Not Acceptable

407

Proxy Authentication Required

408

Request Timeout

409

Conflict

410

Gone

411

Length Required

412

Precondition Failed

413

Content Too Large

414

URI Too Long

415

Unsupported Media Type

416

Range Not Satisfiable

417

Expectation Failed

418

I'm a Teapot

421

Misdirected Request

422

Unprocessable Content

423

Locked

424

Failed Dependency

425

Too Early

428

Precondition Required

429

Too Many Requests

431

Request Header Fields Too Large

451

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