They will never be transparently/fundamentalally managed by the OS alone. The runtime will need to determine how to juggle green threads across multiple OS threads. In that way, this mapping is not inherent.

It can be designed around but that itself is a runtime design decision and I would not say it's akin to default vs custom.

With respect, it's not particularly relevant how you use "inherent". It's a standard usage. Rather than asking the whole rest of the world to change, you should probably learn the definition.