203 Non-Authoritative Information

The request succeeded, but a proxy changed the response the origin server sent.

Class
2xx Successful. The request was received, understood and accepted.
Registered
Yes, in the IANA HTTP status code registry.
Cacheable by default
Yes. A cache may store it without Cache-Control or Expires saying to.
References
RFC 9110 ยง15.3.4 · MDN

Every 2xx code

All HTTP status codes, in one table