Clarity on server actions action Ids changes in next.js 15

[shaunwarman]

From the new next.js 15 blog release it looks like in the server actions security section there is a snippet saying

Secure action IDs: Next.js now creates unguessable, non-deterministic IDs to allow the client to reference and call the Server Action. These IDs are periodically recalculated between builds for enhanced security.

Does this mean that the IDs will be recalculated at runtime and change in production? Or per build? And can there be some added detail on how this is adding security (maybe security through obscurity?). I believe the action IDs are quite random today (just a checksum of the code AFAIK).