MUI has released version 1.0 of its unstyled React user interface (UI) library, Base UI, after two years of development. It ships 35 components with no styling at all. What it does carry is the hard part: keyboard navigation, focus management, the accessibility attributes, and the interaction patterns that are easy to get subtly wrong. It comes from the people behind Radix, Floating UI, and Material UI.
I think the headless approach is the right default for a component library that has to serve many applications for many years. A styled kit looks finished on day one and spends every day after that fighting your design system. A headless library gives you the behavior, which is the same everywhere, and leaves the look to your own tokens, which is the part that is actually yours.
The cost is real: you own the styling work, and a team without a design system will feel it immediately.
My view, after years around shared component libraries, is that the interaction and accessibility logic is where the bugs and the lawsuits live. Taking that from a maintained library and keeping the visual layer is the trade I would make.
Does your component library own its own styling, or did you start from a kit and spend the next year fighting it?
Photo source: https://photos.robertstowe.com/venice