Design systems are infrastructure, not UI kits

Working notes. The full essay is in progress; this is the argument in outline.

The claim

A design system that lives as a Figma library is a UI kit. Infrastructure is different: it is tokenized, themeable, governed, and measured by adoption, not by how complete the component sheet looks.

Evidence

• Facebook Design System sprint: six weeks, three orgs, surface adoption from 19% to 59%, 21 components shipped against a target of 17. The unlock was treating integration as the deliverable, not the component.
• Meta V2 system: 80% adoption and 1.73 million lines of code deleted. Code deletion is an infrastructure metric; no UI kit ever deleted code.
• Pegasus: a system I run as a product, used by 80K+ people. Running one end to end teaches you what governance actually costs.

The outline

1. Tokens before components; themes before variants.
2. Adoption is a funnel, and you have to instrument it.
3. Governance is a product with users, not a police force.
4. The system pays for itself in deleted code or it does not.