A permanent HTTP redirect that preserves the original request method and body.
A 308 is a permanent HTTP redirect with an important method-preservation rule. When a client follows it, the redirected request keeps the original method and body. That matters for requests that send data, not only for ordinary page visits that retrieve information.
A 301 is also a permanent redirect, but some redirect handling can change a POST request into a GET request. A 308 explicitly preserves the request method. Choosing between them can therefore be an application-behavior decision as well as a URL-migration decision. It should be made with the software receiving the redirected request in mind.
For Google Search, a 308 is treated as a permanent redirect, like a 301. It does not offer a special extra ranking benefit. The destination still needs to be the intended replacement, and the redirect must not create a loop or an unnecessary chain.
Takeaway: If your developer or hosting platform uses a 308 for permanent URL normalization, do not assume it is an SEO error because it is less familiar than a 301. Check what it does and whether its destination is correct.
Example
A developer permanently moves an application endpoint that receives POST requests. Preserving the submitted request method and body is part of the application’s requirements, so the redirect type needs to reflect that behavior. An ordinary service-page visit may never expose the difference, which is why checking only a browser page load is insufficient for this case.
What to check
Have the technical owner test representative requests and the receiving application. Do not experiment with redirecting customer submissions merely to change a status code. For normal page migrations, verify the final URL and content just as you would with any permanent redirect.
For more detail, see MDN 308 reference.