What does HTTP status 103 (HTTP_EARLY_HINTS) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: HTTP 103 lets a server send selected response headers before its final response.

Could be also:
Constant	Type	OS
ERROR_TOO_MANY_SEM_REQUESTS	Win32 error	Windows
ECONNABORTED	errno	Linux
ENOPOLICY	errno	Mac
EALREADY	errno	Windows
CONFIG_INITIALIZATION_FAILED	BugCheck Code	Windows

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HTTP_STATUS_PROCESSING	HTTP_STATUS_OK

HTTP_EARLY_HINTS

HTTP 103 is an informational response. It is normally used with Link headers so a user agent can begin preloading resources while the origin server is still preparing the final response.

A client must treat the eventual final response as authoritative. Do not use 103 as an application result or as proof that the requested resource was successfully generated; it only carries early, non-final metadata.

How clients should use 103

A client can use these preliminary headers to begin work such as preconnecting or fetching linked resources while the server prepares the final response. The final response remains authoritative: clients must not treat the 103 response as the completed request, and intermediaries need to preserve the distinction between an informational response and the final status.

RFC 9110: HTTP Semantics

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