RSC was marked stable in Mid 2022 and this major change is still in the process of unfolding through the ecosystem, because of course these things take time. And even though react might be the future, I have a hard time understanding a client side framework that currently becomes more of a server side framework being stable.
By that standard, nothing is stable. New features are added to HTML, the Linux kernel, x86, PHP, etc all the time. In fact, building on top of higher level abstractions can sometime insulate your application from this change too.