Other 4xx codes
All HTTP status codes in ASP.NET Core
4xx Client error
426 Upgrade Required
The server refuses the request over the current protocol and says which one to use in an Upgrade header.
In ASP.NET Core: Rarely used by APIs.
426 in .NET
The StatusCodes constant, HttpStatusCode enum name, reason phrase, class, and how EnsureSuccessStatusCode() and the standard resilience handler treat 426.
| Constant | StatusCodes.Status426UpgradeRequired |
|---|---|
| HttpStatusCode | HttpStatusCode.UpgradeRequired |
| Reason phrase | Kestrel sends Upgrade Required |
| Class | 4xx, client error |
| IsSuccessStatusCode | false |
| EnsureSuccessStatusCode() | throws HttpRequestException: Response status code does not indicate success: 426 (Upgrade Required). |
| Standard resilience handler | does not retry it |
Returning 426
Minimal APIs
Results.StatusCode(StatusCodes.Status426UpgradeRequired)
Results.Problem(statusCode: StatusCodes.Status426UpgradeRequired, detail: "...")Controllers
StatusCode(StatusCodes.Status426UpgradeRequired)
Problem(statusCode: StatusCodes.Status426UpgradeRequired, detail: "...")The ProblemDetails body
What Results.Problem(statusCode: 426) sends (with AddProblemDetails()), as application/problem+json:
{
"type": "https://tools.ietf.org/html/rfc9110#section-15.5.22",
"title": "Upgrade Required",
"status": 426,
"traceId": "0HNA1B2C3D4E5:00000001"
}A controller's Problem(statusCode: 426) sends the same body.
A bare StatusCode(426) in an [ApiController] also gets a ProblemDetails body automatically; Results.StatusCode(426) in a minimal API sends an empty body unless you add UseStatusCodePages().
Every response on this page was recorded from ASP.NET Core 10.0.12 on Kestrel in the Production environment; the HttpClient rows come from .NET 10.0.12 and Microsoft.Extensions.Http.Resilience 10.10.0.